Blogging about Nextflow, computational workflows, containers and cloud computing

Optimizing Nextflow for HPC and Cloud at Scale

  • Ben Sherman
  • 17 January 2024


A Nextflow workflow run consists of the head job (Nextflow itself) and compute tasks (defined in the pipeline script). It is common to request resources for the tasks via process directives such as cpus and memory, but the Nextflow head job also requires compute resources. Most of the time, users don’t need to explicitly define the head job resources, as Nextflow generally does a good job of allocating resources for itself. For very large workloads, however, head job resource sizing becomes much more important.

In this article, we will help you understand how the Nextflow head job works and show you how to tune head job resources such as CPUs and memory for your use case.

Nextflow and nf-core Mentorship, Round 3

  • Marcel Ribeiro-Dantas
  • 13 November 2023

Mentorship rocket.

Nextflow and nf-core mentorship rocket.

With the third round of the Nextflow and nf-core mentorship program now behind us, it's time to pop the confetti and celebrate the outstanding achievements of our latest group of mentors and mentees!

As with the first and second rounds of the program, we received hundreds of applications from all over the world. Mentors and mentees were matched based on compatible interests and time zones and set off to work on a project of their choosing. Pairs met regularly to work on their projects and reported back to the group to discuss their progress every month.

The mentor-mentee duos chose to tackle many interesting projects during the program. From learning how to develop pipelines with Nextflow and nf-core, setting up Nextflow on their institutional clusters, and translating Nextflow training .. (click here to read more)

Nextflow Summit 2023 Recap

  • Noel Ortiz
  • 25 October 2023

Five days of Nextflow Awesomeness in Barcelona

On Friday, Oct 20, we wrapped up our hackathon and Nextflow Summit in Barcelona, Spain. By any measure, this year’s Summit was our best community event ever, drawing roughly 900 attendees across multiple channels, including in-person attendees, participants in our #summit-2023 Slack channel, and Summit Livestream viewers on YouTube.

The Summit drew attendees, speakers, and sponsors from around the world. Over the course of the three-day event, we heard from dozens of impressive speakers working at the cutting edge of life sciences from academia, research, healthcare providers, biotechs, and cloud providers, including:

  • Australian BioCommons
  • Genomics England
  • Pixelgen Technologies
  • University of Tennessee Health Science Center
  • Amazon Web Services
  • Quantitative Biology Center - University of Tübingen
  • Biomodal
  • Matterhorn Studio
  • Centre for Genomic Regulation (CRG)
  • Heidelberg University Hospital
  • MemVerge
  • University of Cambridge
  • Oxford Nanopore Technologies
  • Medical University of Innsbruck
  • Sano Genetics
  • Institute of .. (click here to read more)


  • Phil Ewels
  • 18 October 2023

We are very excited to introduce the Seqera community forum - the new home of the Nextflow community!

The growth of the Nextflow community over recent years has been phenomenal. The Nextflow Slack organization was launched in early 2022 and has already reached a membership of nearly 3,000 members. As we look ahead to growing to 5,000 and even 50,000, we are making a new tool available to the community: a community forum.

We expect the new forum to coexist with the Nextflow Slack. The forum will be great at medium-format discussion, whereas Slack is largely designed for short-term ephemeral conversations. We want to support this growth of the community and believe the new forum will allow us to scale.

Discourse is an open-source, web-based platform designed for online community discussions and forum-style interactions. Discourse offers a user-friendly interface, real-time notifications, and a wide range .. (click here to read more)

Introducing the Nextflow Ambassador Program

  • Marcel Ribeiro-Dantas
  • 18 October 2023

We are excited to announce the launch of the Nextflow Ambassador Program, a worldwide initiative designed to foster collaboration, knowledge sharing, and community growth. It is intended to recognize and support the efforts of our community leaders and marks another step forward in our mission to advance scientific research and empower researchers.

Nextflow ambassadors will play a vital role in:

  • Sharing Knowledge: Ambassadors provide valuable insights and best practices to help users make the most of Nextflow by writing training material and blog posts, giving seminars and workshops, organizing hackathons and meet-ups, and helping with community support.
  • Fostering Collaboration: As knowledgeable members of our community, ambassadors facilitate connections among users and developers, enabling collaboration on community projects, such as nf-core pipelines, sub-workflows, and modules, among other things, in the Nextflow ecosystem.
  • Community Growth: Ambassadors help expand and enrich the Nextflow community, making it more .. (click here to read more)

Geraldine Van der Auwera joins Seqera

  • Geraldine Van der Auwera
  • 11 October 2023

I’m excited to announce that I’m joining Seqera as Lead Developer Advocate. My mission is to support the growth of the Nextflow user community, especially in the USA, which will involve running community events, conducting training sessions, managing communications and working globally with our partners across the field to ensure Nextflow users have what they need to be successful. I’ll be working remotely from Boston, in collaboration with Paolo, Phil and the rest of the Nextflow team.

Some of you may already know me from my previous job at the Broad Institute, where I spent a solid decade doing outreach and providing support for the genomics research community, first for GATK, then for WDL and Cromwell, and eventually Terra. A smaller subset might have come across the O’Reilly book I co-authored, Genomics on the Cloud.

This new mission is very much a continuation of .. (click here to read more)

Nextflow goes to university!

  • Marcel Ribeiro-Dantas
  • 24 July 2023

The Nextflow project originated from within an academic research group, so perhaps it’s no surprise that education is an essential part of the Nextflow and nf-core communities. Over the years, we have established several regular training resources: we have a weekly online seminar series called nf-core/bytesize and run hugely popular bi-annual Nextflow and nf-core community training online. In 2022, Seqera established a new community and growth team, funded in part by a grant from the Chan Zuckerberg Initiative “Essential Open Source Software for Science” grant. We are all former bioinformatics researchers from academia and part of our mission is to build resources and programs to support academic institutions. We want to help to provide leading edge, high-quality, Nextflow and nf-core training for Masters and Ph.D. students in Bioinformatics and other related fields.

We recently held one of our first such projects, a collaboration with the Bioinformatics Multidisciplinary .. (click here to read more)

A Nextflow-Docker Murder Mystery: The mysterious case of the “OOM killer”

  • Graham Wright
  • 19 June 2023

Most support tickets crossing our desks don’t warrant a blog article. However, occasionally we encounter a genuine mystery—a bug so pervasive and vile that it threatens innocent containers and pipelines everywhere. Such was the case of the OOM killer.

In this article, we alert our colleagues in the Nextflow community to the threat. We also discuss how to recognize the killer’s signature in case you find yourself dealing with a similar murder mystery in your own cluster or cloud.

Reflecting on ten years of Nextflow awesomeness

  • Noel Ortiz
  • 06 June 2023

There's been a lot of water under the bridge since the first release of Nextflow in July 2013. From its humble beginnings at the Centre for Genomic Regulation (CRG) in Barcelona, Nextflow has evolved from an upstart workflow orchestrator to one of the most consequential projects in open science software (OSS). Today, Nextflow is downloaded 120,000+ times monthly, boasts vibrant user and developer communities, and is used by leading pharmaceutical, healthcare, and biotech research firms.

On the occasion of Nextflow's anniversary, I thought it would be fun to share some perspectives and point out how far we've come as a community. I also wanted to recognize the efforts of Paolo Di Tommaso and the many people who have contributed enormous time and effort to make Nextflow what it is today.

A decade of innovation

Bill Gates is credited with observing that "people often overestimate what they can do in one year, but .. (click here to read more)

Nextflow on BIG IRON: Twelve tips for improving the effectiveness of pipelines on HPC clusters

  • Gordon Sissons
  • 26 May 2023

With all the focus on cloud computing, it's easy to forget that most Nextflow pipelines still run on traditional HPC clusters. In fact, according to our latest State of the Workflow 2023 community survey, 62.8% of survey respondents report running Nextflow on HPC clusters, and 75% use an HPC workload manager.1 While the cloud is making gains, traditional clusters aren't going away anytime soon.

Tapping cloud infrastructure offers many advantages in terms of convenience and scalability. However, for organizations with the capacity to manage in-house clusters, there are still solid reasons to run workloads locally:

  • Guaranteed access to resources. Users don't need to worry about shortages of particular instance types, spot instance availability, or exceeding cloud spending caps.
  • Predictable pricing. Organizations are protected against price inflation and unexpected rate increases by capitalizing assets and depreciating them over time.
  • Reduced costs. Contrary to conventional wisdom, well-managed, highly-utilized, on-prem clusters are .. (click here to read more)

Selecting the right storage architecture for your Nextflow pipelines

  • Paolo Di Tommaso
  • 04 May 2023

In this article we present the various storage solutions supported by Nextflow including on-prem and cloud file systems, parallel file systems, and cloud object stores. We also discuss Fusion file system 2.0, a new high-performance file system that can help simplify configuration, improve throughput, and reduce costs in the cloud.

At one time, selecting a file system for distributed workloads was straightforward. Through the 1990s, the Network File System (NFS), developed by Sun Microsystems in 1984, was pretty much the only game in town. It was part of every UNIX distribution, and it presented a standard POSIX interface, meaning that applications could read and write data without modification. Dedicated NFS servers and NAS filers became the norm in most clustered computing environments.

For organizations that outgrew the capabilities of NFS, other POSIX file systems emerged. These included parallel file systems such as Lustre, PVFS, OpenZFS, BeeGFS, and .. (click here to read more)

Celebrating our largest international training event and hackathon to date

  • Phil Ewels
  • 25 April 2023

In mid-March, we conducted our bi-annual Nextflow and nf-core training and hackathon in what was unquestionably our best-attended community events to date. This year we had an impressive 1,345 participants attend the training from 76 countries. Attendees came from far and wide — from Algeria to Andorra to Zambia to Zimbabwe!

Among our event attendees, we observed the following statistics:

  • 40% were 30 years old or younger, pointing to a young cohort of Nextflow users;
  • 55.3% identified as male vs. 40% female, highlighting our growing diversity;
  • 68.2% came from research institutions;
  • 71.4% were attending their first Nextflow training event;
  • 96.7% had never attended a Nextflow hackathon.

Read on to learn more about these exciting events. If you missed it, you can still watch the Nextflow & nf-core training at your convenience.

Nextflow and nf-core Mentorship, Round 2

  • Chris Hakkaart
  • 17 April 2023


Mentorship rocket.

Nextflow and nf-core mentorship rocket.

The global Nextflow and nf-core community is thriving with strong engagement in several countries. As we continue to expand and grow, we remain committed to prioritizing inclusivity and actively reaching groups with low representation.

Thanks to the support of our Chan Zuckerberg Initiative Diversity and Inclusion grant, we established an international Nextflow and nf-core mentoring program. With the second round of the mentorship program now complete, we celebrate the success of the most recent cohort of mentors and mentees.

From hundreds of applications, thirteen pairs of mentors and mentees were chosen for the second round of the program. For the past four months, they met regularly to collaborate on Nextflow or nf-core projects. The project scope was left up to the mentees, enabling them to work on any project aligned with .. (click here to read more)

The State of Kubernetes in Nextflow

  • Ben Sherman
  • 10 March 2023

Hi, my name is Ben, and I’m a software engineer at Seqera Labs. I joined Seqera in November 2021 after finishing my Ph.D. at Clemson University. I work on a number of things at Seqera, but my primary role is that of a Nextflow core contributor.

I have run Nextflow just about everywhere, from my laptop to my university cluster to the cloud and Kubernetes. I have written Nextlfow pipelines for bioinformatics and machine learning, and I even wrote a pipeline to run other Nextflow pipelines for my dissertation research. While I tried to avoid contributing code to Nextflow as a student (I had enough work already), now I get to work on it full-time!

Which brings me to the topic of this post: Nextflow and Kubernetes.

One of my first contributions was a “best practices guide” for running Nextflow on Kubernetes. The guide has helped many people, but for me .. (click here to read more)

Learn Nextflow in 2023

  • Evan Floden
  • 24 February 2023

In 2023, the world of Nextflow is more exciting than ever! With new resources constantly being released, there is no better time to dive into this powerful tool. From a new Software Carpentries’ course to recordings of mutiple nf-core training events to new tutorials on Wave and Fusion, the options for learning Nextflow are endless.

We've compiled a list of the best resources in 2023 to make your journey to Nextflow mastery as seamless as possible. And remember, Nextflow is a community-driven project. If you have suggestions or want to contribute to this list, head to the GitHub page and make a pull request.

Before you start

Before learning Nextflow, you should be comfortable with the Linux command line and be familiar with some basic scripting languages, such as Perl or Python. The beauty of Nextflow is that task logic can be written in your language of choice. You .. (click here to read more)

Get started with Nextflow on Google Cloud Batch

  • Marcel Ribeiro-Dantas
  • 01 February 2023

We have talked about Google Cloud Batch before. Not only that, we were proud to announce Nextflow support to Google Cloud Batch right after it was publicly released, back in July 2022. How amazing is that? But we didn't stop there! The Nextflow official documentation also provides a lot of useful information on how to use Google Cloud Batch as the compute environment for your Nextflow pipelines. Having said that, feedback from the community is valuable, and we agreed that in addition to the documentation, teaching by example, and in a more informal language, can help many of our users. So, here is a tutorial on how to use the Batch service of the Google Cloud Platform with Nextflow 🥳

Running an RNAseq pipeline with Google Cloud Batch

Welcome to our RNAseq tutorial using Nextflow and Google Cloud Batch! RNAseq is a powerful technique for studying gene expression and is .. (click here to read more)

Analyzing caching behavior of pipelines

  • Abhinav Sharma
  • 10 November 2022

The ability to resume an analysis (i.e. caching) is one of the core strengths of Nextflow. When developing pipelines, this allows us to avoid re-running unchanged processes by simply appending -resume to the nextflow run command. Sometimes, tasks may be repeated for reasons that are unclear. In these cases it can help to look into the caching mechanism, to understand why a specific process was re-run.

We have previously written about Nextflow's resume functionality as well as some troubleshooting strategies to gain more insights on the caching behavior.

In this post, we will take a more hands-on approach and highlight some strategies which we can use to understand what is causing a particular process (or processes) to re-run, instead of using the cache from previous runs of the pipeline. To demonstrate the process, we will introduce a minor change into one of the process definitions in the the click here to read more)

Nextflow Summit 2022 Recap

  • Noel Ortiz
  • 03 November 2022

Three days of Nextflow goodness in Barcelona

After a three-year COVID-related hiatus from in-person events, Nextflow developers and users found their way to Barcelona this October for the 2022 Nextflow Summit. Held at Barcelona’s iconic Agbar tower, this was easily the most successful Nextflow community event yet!

The week-long event kicked off with 50 people participating in a hackathon organized by nf-core beginning on October 10th. The hackathon tackled several cutting-edge projects with developer teams focused on various aspects of nf-core including documentation, subworkflows, pipelines, DSL2 conversions, modules, and infrastructure. The Nextflow Summit began mid-week attracting nearly 600 people, including 165 attending in person and another 433 remotely. The YouTube live streams have now collected over two and half thousand views. Just prior to the summit, three virtual Nextflow training events were also run with separate sessions for the Americas, .. (click here to read more)

Rethinking containers for cloud native pipelines

  • Paolo Di Tommaso
  • 13 October 2022

Containers have become an essential part of well-structured data analysis pipelines. They encapsulate applications and dependencies in portable, self-contained packages that can be easily distributed. Containers are also key to enabling predictable and reproducible results.

Nextflow was one of the first workflow technologies to fully embrace containers for data analysis pipelines. Community curated container collections such as BioContainers also helped speed container adoption.

However, the increasing complexity of data analysis pipelines and the need to deploy them across different clouds and platforms pose new challenges. Today, workflows may comprise dozens of distinct container images. Pipeline developers must manage and maintain these containers and ensure that their functionality precisely aligns with the requirements of every pipeline task.

Also, multi-cloud deployments and the increased use of private container registries further increase complexity for developers. Building and maintaining containers, pushing them to multiple registries, and dealing with platform-specific authentication schemes are tedious, time .. (click here to read more)

Turbo-charging the Nextflow command line with Fig!

  • Marcel Ribeiro-Dantas
  • 22 September 2022

Nextflow is a powerful workflow manager that supports multiple container technologies, cloud providers and HPC job schedulers. It shouldn't be a surprise that wide ranging functionality leads to a complex interface, but comes with the drawback of many subcommands and options to remember. For a first-time user (and sometimes even for some long-time users) it can be difficult to remember everything. This is not a new problem for the command-line; even very common applications such as grep and tar are famous for having a bewildering array of options.

xkcd charge making fun of tar tricky command line arguments

Many tools have sprung up to make the command-line more user friendly, such as tldr pages and rich-click. Fig is one such tool that adds powerful autocomplete functionality to your terminal. Fig gives you graphical popups with color-coded contexts more dynamic than shaded text for recent commands or long .. (click here to read more)

Nextflow and nf-core mentorship, Round 1

  • Chris Hakkaart
  • 18 September 2022


Word cloud

Word cloud of scientific interest keywords, averaged across all applications.

Our recent The State of the Workflow 2022: Community Survey Results showed that Nextflow and nf-core have a strong global community with a high level of engagement in several countries. As the community continues to grow, we aim to prioritize inclusivity for everyone through active outreach to groups with low representation.

Thanks to funding from our Chan Zuckerberg Initiative Diversity and Inclusion grant we established an international Nextflow and nf-core mentoring program with the aim of empowering those from underrepresented groups. With the first round of the mentorship now complete, we look back at the success of the program so far.

From almost 200 applications, five pairs of mentors and mentees were selected for the first round of the program. Over the following .. (click here to read more)

Deploy Nextflow Pipelines with Google Cloud Batch!

  • Paolo Di Tommaso
  • 13 July 2022

A key feature of Nextflow is the ability to abstract the implementation of data analysis pipelines so they can be deployed in a portable manner across execution platforms.

As of today, Nextflow supports a rich variety of HPC schedulers and all major cloud providers. Our goal is to support new services as they emerge to enable Nextflow users to take advantage of the latest technology and deploy pipelines on the compute environments that best fit their requirements.

For this reason, we are delighted to announce that Nextflow now supports Google Cloud Batch, a new fully managed batch service just announced for beta availability by Google Cloud.

A New On-Ramp to the Google Cloud

Google Cloud Batch is a comprehensive cloud service suitable for multiple use cases, including HPC, AI/ML, and data processing. While it is similar to the Google Cloud Life Sciences API, used by many Nextflow users today, Google Cloud .. (click here to read more)

Nextflow Summit 2022

  • Phil Ewels
  • 17 June 2022

As recently announced, we are super excited to host a new Nextflow community event late this year! The Nextflow Summit will take place October 12-14, 2022 at the iconic Torre Glòries in Barcelona, with an associated nf-core hackathon beforehand.

Call for abstracts

Today we’re excited to open the call for abstracts! We’re looking for talks and posters about anything and everything happening in the Nextflow world. Specifically, we’re aiming to shape the program into four key areas:

  • Nextflow: central tool / language / plugins
  • Community: pipelines / applications / use cases
  • Ecosystem: infrastructure / environments
  • Software: containers / tool packaging

Speaking at the summit will primarily be in-person, but we welcome posters from remote attendees. Posters will be submitted digitally and available online during and after the event. Talks will be streamed live and be available after the event.

.. (click here to read more)

Evolution of the Nextflow runtime

  • Paolo Di Tommaso
  • 24 March 2022

Software development is a constantly evolving process that requires continuous adaptation to keep pace with new technologies, user needs, and trends. Likewise, changes are needed in order to introduce new capabilities and guarantee a sustainable development process.

Nextflow is no exception. This post will summarise the major changes in the evolution of the framework over the next 12 to 18 months.

Java baseline version

Nextflow runs on top of Java (or, more precisely, the Java virtual machine). So far, Java 8 has been the minimal version required to run Nextflow. However, this version was released 8 years ago and is going to reach its end-of-life status at the end of this month. For this reason, as of version 22.01.x-edge and the upcoming stable release 22.04.0, Nextflow will require Java version 11 or later for its execution. This also allows the introduction of new capabilities provided by the modern Java runtime.

Tip: .. (click here to read more)

Nextflow’s community is moving to Slack!

  • Paolo Di Tommaso
  • 22 February 2022

“Software communities don’t just write code together. They brainstorm feature ideas, help new users get their bearings, and collaborate on best ways to use the software.…conversations need their own place" - GitHub Satellite Blog 2020

The Nextflow community channel on Gitter has grown substantially over the last few years and today has more than 1,300 members.

I still remember when a former colleague proposed the idea of opening a Nextflow channel on Gitter. At the time, I didn't know anything about Gitter, and my initial response was : "would that not be a waste of time?".

Fortunately, I took him up on his suggestion and the Gitter channel quickly became an important resource for all Nextflow developers and a key factor to its success.

Where the future lies

As the Nextflow community continues to grow, we realize that we have reached the limit of .. (click here to read more)

Learning Nextflow in 2022

  • Evan Floden
  • 21 January 2022

A lot has happened since we last wrote about how best to learn Nextflow, over a year ago. Several new resources have been released including a new Nextflow Software Carpentries course and an excellent write-up by 23andMe.

We have collated some links below from a diverse collection of resources to help you on your journey to learn Nextflow. Nextflow is a community-driven project - if you have any suggestions, please make a pull request to this page on GitHub.

Without further ado, here is the definitive guide for learning Nextflow in 2022. These resources will support anyone in the journey from total beginner to Nextflow expert.


Before you start writing Nextflow pipelines, we recommend that you are comfortable with using the command-line and understand the basic concepts of scripting languages such as Python or Perl. Nextflow is widely used for bioinformatics applications, and scientific data analysis. The examples and .. (click here to read more)

Configure Git private repositories with Nextflow

  • Abhinav Sharma
  • 21 October 2021

Git has become the de-facto standard for source-code version control system and has seen increasing adoption across the spectrum of software development.

Nextflow provides builtin support for Git and most popular Git hosting platforms such as GitHub, GitLab and Bitbucket between the others, which streamline managing versions and track changes in your pipeline projects and facilitate the collaboration across different users.

In order to access public repositories Nextflow does not require any special configuration, just use the http URL of the pipeline project you want to run in the run command, for example:

nextflow run 

However to allow Nextflow to access private repositories you will need to specify the repository credentials, and the server hostname in the case of self-managed Git server installations.

Configure access to private repositories

This is done through a file name scm placed in the $HOME/.nextflow/ directory, containing the credentials and other details for accessing a .. (click here to read more)

Setting up a Nextflow environment on Windows 10

  • Evan Floden
  • 13 October 2021

For Windows users, getting access to a Linux-based Nextflow development and runtime environment used to be hard. Users would need to run virtual machines, access separate physical servers or cloud instances, or install packages such as Cygwin or Wubi. Fortunately, there is now an easier way to deploy a complete Nextflow development environment on Windows.

The Windows Subsystem for Linux (WSL) allows users to build, manage and execute Nextflow pipelines on a Windows 10 laptop or desktop without needing a separate Linux machine or cloud VM. Users can build and test Nextflow pipelines and containerized workflows locally, on an HPC cluster, or their preferred cloud service, including AWS Batch and Azure Batch.

This document provides a step-by-step guide to setting up a Nextflow development environment on Windows 10.

High-level Steps

The steps described in this guide are as follows:

  • Install Windows PowerShell
  • Configure the Windows Subsystem for Linux (WSL2)
  • Obtain and .. (click here to read more)

Introducing Nextflow support for SQL databases

  • Paolo Di Tommaso
  • 16 September 2021

The recent tweet introducing the Nextflow support for SQL databases raised a lot of positive reaction. In this post, I want to describe more in detail how this extension works.

Nextflow was designed with the idea to streamline the deployment of complex data pipelines in a scalable, portable and reproducible manner across different computing platforms. To make this all possible, it was decided the resulting pipeline and the runtime should be self-contained i.e. to not depend on separate services such as database servers.

This makes the resulting pipelines easier to configure, deploy, and allows for testing them using CI services, which is a critical best practice for delivering high-quality and stable software.

Another important consequence is that Nextflow pipelines do not retain the pipeline state on separate storage. Said in a different way, the idea was - and still is - to promote stateless pipeline execution in which the .. (click here to read more)

Five more tips for Nextflow user on HPC

  • Kevin Sayers
  • 15 June 2021

In May we blogged about Five Nextflow Tips for HPC Users and now we continue the series with five additional tips for deploying Nextflow with on HPC batch schedulers.

1. Use the scratch directive

To allow the pipeline tasks to share data with each other, Nextflow requires a shared file system path as a working directory. When using this model, a common recommendation is to use the node's local scratch storage as the job working directory to avoid unnecessary use of the network shared file system and achieve better performance.

Nextflow implements this best-practice which can be enabled by adding the following setting in your nextflow.config file.

process.scratch = true 

When using this option, Nextflow: * Creates a unique directory in the computing node's local /tmp or the path assigned by your cluster via the TMPDIR environment variable. * Creates a symlink for each input file required by the job execution. .. (click here to read more)

5 Nextflow Tips for HPC Users

  • Kevin Sayers
  • 13 May 2021

Nextflow is a powerful tool for developing scientific workflows for use on HPC systems. It provides a simple solution to deploy parallelized workloads at scale using an elegant reactive/functional programming model in a portable manner.

It supports the most popular workload managers such as Grid Engine, Slurm, LSF and PBS, among other out-of-the-box executors, and comes with sensible defaults for each. However, each HPC system is a complex machine with its own characteristics and constraints. For this reason you should always consult your system administrator before running a new piece of software or a compute intensive pipeline that spawns a large number of jobs.

In this series of posts, we will be sharing the top tips we have learned along the way that should help you get results faster while keeping in the good books of your sys admins.

1. Don't forget the executor

Nextflow, by default, spawns parallel task executions in .. (click here to read more)

6 Tips for Setting Up Your Nextflow Dev Environment

  • Evan Floden
  • 04 March 2021

This blog follows up the Learning Nextflow in 2020 blog post.

This guide is designed to walk you through a basic development setup for writing Nextflow pipelines.

1. Installation

Nextflow runs on any Linux compatible system and MacOS with Java installed. Windows users can rely on the Windows Subsystem for Linux. Installing Nextflow is straightforward. You just need to download the nextflow executable. In your terminal type the following commands:

$ curl | bash $ sudo mv nextflow /usr/local/bin 

The first line uses the curl command to download the nextflow executable, and the second line moves the executable to your PATH. Note /usr/local/bin is the default for MacOS, you might want to choose ~/bin or /usr/bin depending on your PATH definition and operating system.

2. Text Editor or IDE?

Nextflow pipelines can be written in any plain text editor. I'm personally a bit of a Vim fan, however, the advent of .. (click here to read more)

Introducing Nextflow for Azure Batch

  • Paolo Di Tommaso
  • 22 February 2021

When the Nextflow project was created, one of the main drivers was to enable reproducible data pipelines that could be deployed across a wide range of execution platforms with minimal effort as well as to empower users to scale their data analysis while facilitating the migration to the cloud.

Throughout the years, the computing services provided by cloud vendors have evolved in a spectacular manner. Eight years ago, the model was focused on launching virtual machines in the cloud, then came containers and then the idea of serverless computing which changed everything again. However, the power of the Nextflow abstraction consists of hiding the complexity of the underlying platform. Through the concept of executors, emerging technologies and new platforms can be easily adapted with no changes required to user pipelines.

With this in mind, we could not be more excited to announce that over the past months we have been working with .. (click here to read more)

Learning Nextflow in 2020

  • Evan Floden & Alain Coletta
  • 01 December 2020

With the year nearly over, we thought it was about time to pull together the best-of-the-best guide for learning Nextflow in 2020. These resources will support anyone in the journey from total noob to Nextflow expert so this holiday season, give yourself or someone you know the gift of learning Nextflow!

Prerequisites to get started

We recommend that learners are comfortable with using the command line and the basic concepts of a scripting language such as Python or Perl before they start writing pipelines. Nextflow is widely used for bioinformatics applications, and the examples in these guides often focus on applications in these topics. However, Nextflow is now adopted in a number of data-intensive domains such as radio astronomy, satellite imaging and machine learning. No domain expertise is expected.

Time commitment

We estimate that the speediest of learners can complete the material in around 12 hours. It all depends on your background and how .. (click here to read more)

More syntax sugar for Nextflow developers!

  • Paolo Di Tommaso
  • 03 November 2020

The latest Nextflow version 2020.10.0 is the first stable release running on Groovy 3.

The first benefit of this change is that now Nextflow can be compiled and run on any modern Java virtual machine, from Java 8, all the way up to the latest Java 15!

Along with this, the new Groovy runtime brings a whole lot of syntax enhancements that can be useful in the everyday life of .. (click here to read more)

The Nextflow CLI - tricks and treats!

  • Abhinav Sharma
  • 22 October 2020

For most developers, the command line is synonymous with agility. While tools such as Nextflow Tower are opening up the ecosystem to a whole new set of users, the Nextflow CLI remains a bedrock for pipeline development. The CLI in Nextflow has been the core interface since the beginning; however, its full functionality was never extensively documented. Today we are excited to release the first iteration of the CLI documentation available on the Nextflow website.

And given Halloween is just around the corner, in this blog post we'll take a look at 5 CLI tricks and examples which will make your life easier in designing, executing and debugging data pipelines. We are also giving away 5 limited-edition Nextflow hoodies and sticker packs so you can code in style this Halloween season!

1. Invoke a remote pipeline execution with the latest revision

Nextflow facilitates easy collaboration and re-use of existing pipelines in .. (click here to read more)

Nextflow DSL 2 is here!

  • Paolo Di Tommaso
  • 24 July 2020

We are thrilled to announce the stable release of Nextflow DSL 2 as part of the latest 20.07.1 version!

Nextflow DSL 2 represents a major evolution of the Nextflow language and makes it possible to scale and modularise your data analysis pipeline while continuing to use the Dataflow programming paradigm that characterises the Nextflow processing model.

We spent more than one year collecting user feedback and making sure that DSL 2 would naturally fit the programming experience Nextflow developers are used to.

DLS 2 in a nutshell

Backward compatibility is a paramount value, for this reason the changes introduced in the syntax have been minimal and above all, guarantee the support of all existing applications. DSL 2 will be an opt-in feature for at least the next 12 to 18 months. After this transitory period, we plan to make it the default Nextflow execution mode.

As of today, to use DSL .. (click here to read more)

Easy provenance reporting

  • Evan Floden
  • 29 August 2019

Continuing our series on understanding Nextflow resume, we wanted to delve deeper to show how you can report which tasks contribute to a given workflow output.

Easy provenance reports

When provided with a run name or session ID, the log command can return useful information about a pipeline execution. This can be composed to track the provenance of a workflow result.

When supplying a run name or session ID, the log command .. (click here to read more)

Troubleshooting Nextflow resume

  • Evan Floden
  • 01 July 2019

This two-part blog aims to help users understand Nextflow’s powerful caching mechanism. Part one describes how it works whilst part two will focus on execution provenance and troubleshooting. You can read part one here.

Troubleshooting resume

If your workflow execution is not resumed as expected, there exists several strategies to debug the problem.

Modified input file(s)

Make sure that there has been no change in your input files. Don’t forget the unique task hash is computed by taking into account the complete file path, the last modified timestamp and the file size. If any of these change, the workflow will be re-executed, even if the input content is the same.

A process modifying one or more inputs

A process should never alter input files. When this happens, the future execution of tasks will be invalidated for the same reason explained in the previous point.

Inconsistent input file attributes

Some shared file system, such as NFS, may .. (click here to read more)

Demystifying Nextflow resume

  • Evan Floden
  • 24 June 2019

This two-part blog aims to help users understand Nextflow’s powerful caching mechanism. Part one describes how it works whilst part two will focus on execution provenance and troubleshooting. You can read part two here

Task execution caching and checkpointing is an essential feature of any modern workflow manager and Nextflow provides an automated caching mechanism with every workflow execution. When using the -resume flag, successfully completed tasks are skipped and the previously cached results are used in downstream tasks. But understanding the specifics of how it works and debugging situations when the behaviour is not as expected is a common source of frustration.

The mechanism works by assigning a unique ID to each task. This unique ID is used to create a separate execution directory, called the working directory, where the tasks are executed and the results stored. A task’s unique ID is generated as a 128-bit hash number obtained from .. (click here to read more)

One more step towards Nextflow modules

  • Paolo Di Tommaso
  • 22 May 2019

The ability to create components, libraries or module files has been among the most requested feature ever over the years.

For this reason, today we are very happy to announce that a preview implementation of the modules feature has been merged on master branch of the project and included in the 19.05.0-edge release.

The implementation of this feature has opened the possibility for many fantastic improvements to Nextflow and its syntax. We are extremely excited as it results in a radical new way of writing Nextflow applications! So much so, that we are referring to these changes as DSL 2.

Enabling DSL 2 syntax

Since this is still a preview technology and, above all, to not break any existing applications, to enable the new syntax you will need to add the following line at the beginning of your workflow script:


Module files

A module file simply consists of one .. (click here to read more)

Nextflow 19.04.0 stable release is out!

  • Paolo Di Tommaso
  • 18 April 2019

We are excited to announce the new Nextflow 19.04.0 stable release!

This version includes numerous bug fixes, enhancement and new features.

Rich logging

In this release, we are making the new interactive rich output using ANSI escape characters as the default logging option. This produces a much more readable and easy to follow log of the running workflow execution.

The ANSI log is implicitly disabled when the nextflow is launched in the background i.e. when using the -bg option. It can also be explicitly disabled using the -ansi-log false option or setting the NXF_ANSI_LOG=false variable in your launching environment.

NCBI SRA data source

The support for NCBI SRA archive was introduced in the previous edge release. Given the very positive reaction, we are graduating this feature into the stable release for general availability.


This version includes also a new Git repository provider for the Gitea self-hosted source .. (click here to read more)

Edge release 19.03: The Sequence Read Archive & more!

  • Evan Floden
  • 19 March 2019

It's time for the monthly Nextflow release for March, edge version 19.03. This is another great release with some cool new features, bug fixes and improvements.

SRA channel factory

This sees the introduction of the long-awaited sequence read archive (SRA) channel factory. The SRA is a key public repository for sequencing data and run in coordination between The National Center for Biotechnology Information (NCBI), The European Bioinformatics Institute (EBI) and the DNA Data Bank of Japan (DDBJ).

This feature originates all the way back in 2015 and was worked on during a 2018 Nextflow hackathon. It was brought to fore again thanks to the release of Phil Ewels' excellent SRA Explorer. The SRA channel factory allows users to pull read data in FASTQ format directly from SRA by referencing a study, accession ID or even a keyword. It works in a similar way to fromFilePairs, returning a sample ID .. (click here to read more)

Bringing Nextflow to Google Cloud Platform with WuXi NextCODE

  • Paolo Di Tommaso
  • 18 December 2018

This is a guest post authored by Halli Bjornsson, Head of Product Development Operations at WuXi NextCODE and Jonathan Sheffi, Product Manager, Biomedical Data at Google Cloud.

Google Cloud and WuXi NextCODE are dedicated to advancing the state of the art in biomedical informatics, especially through open source, which allows developers to collaborate broadly and deeply.

WuXi NextCODE is itself a user of Nextflow, and Google Cloud has many customers that use Nextflow. Together, we’ve collaborated to deliver Google Cloud Platform (GCP) support for Nextflow using the Google Pipelines API. Pipelines API is a managed computing service that allows the execution of containerized workloads .. (click here to read more)

Goodbye zero, Hello Apache!

  • Paolo Di Tommaso
  • 24 October 2018

Today marks an important milestone in the Nextflow project. We are thrilled to announce three important changes to better meet users’ needs and ground the project on a solid foundation upon which to build a vibrant ecosystem of tools and data analysis applications for genomic research and beyond.

Apache license

Nextflow was originally licensed as GPLv3 open source software more than five years ago. GPL is designed to promote the adoption and spread of open source software and culture. On the other hand it has also some controversial side-effects, such as the one on derivative works and legal implications which make the use of GPL released software a headache in many organisations. We have previously discussed these concerns in this blog post and, after community feedback, have opted to change the project license to Apache 2.0.

This is a popular permissive free software license written by .. (click here to read more)

Nextflow meets Dockstore

  • Paolo Di Tommaso
  • 18 September 2018

This post is co-authored with Denis Yuen, lead of the Dockstore project at the Ontario Institute for Cancer Research

One key feature of Nextflow is the ability to automatically pull and execute a workflow application directly from a sharing platform such as GitHub. We realised this was critical to allow users to properly track code changes and releases and, above all, to enable the seamless sharing of workflow projects.

Nextflow never wanted to implement its own centralised workflow registry because we thought that in order for a registry to be viable and therefore useful, it should be technology agnostic and it should be driven by a consensus among the wider user community.

This is exactly what the Dockstore project is designed for and for this reason we are thrilled to announce that Dockstore has just released the support for Nextflow workflows in its latest release! .. (click here to read more)

Clarification about the Nextflow license

  • Paolo Di Tommaso
  • 20 July 2018

Over past week there was some discussion on social media regarding the Nextflow license and its impact on users' workflow applications.

What's the problem with GPL?

Nextflow has been released under the GPLv3 license since its early days over 5 years ago. GPL is a very popular open source licence used by many projects (like, .. (click here to read more)

Conda support has landed!

  • Paolo Di Tommaso
  • 05 June 2018

Nextflow aims to ease the development of large scale, reproducible workflows allowing
developers to focus on the main application logic and to rely on best community tools and best practices.

For this reason we are very excited to announce that the latest Nextflow version (0.30.0) finally provides built-in support for Conda.

Conda is a popular package manager that simplifies the installation of software packages and the configuration of complex software environments. Above all, it provides access to large tool and software package collections maintained by domain specific communities such as Bioconda and BioBuild.

The native integration with Nextflow allows researchers to develop workflow applications in a rapid and easy repeatable manner, reusing community tools, whilst taking advantage of the configuration flexibility, portability and scalability provided by Nextflow.

How it works

Nextflow automatically creates and activates the Conda environment(s) given the dependencies specified by each process.

Dependencies are specified by using the click here to read more)

Nextflow turns five! Happy birthday!

  • Evan Floden
  • 03 April 2018

Nextflow is growing up. The past week marked five years since the first commit of the project on GitHub. Like a parent reflecting on their child attending school for the first time, we know reaching this point hasn’t been an entirely solo journey, despite Paolo's best efforts!

A lot has happened recently and we thought it was time to highlight some of the recent evolutions. We also take the opportunity to extend the warmest of thanks to all those who have contributed to the development of Nextflow as well as the fantastic community of users who consistently provide ideas, feedback and the occasional late night banter on the Gitter channel.

Here are a few neat developments churning out of the birthday cake mix.


nf-core is a community effort to provide a home for high quality, production-ready, curated analysis pipelines built using Nextflow. The project has been initiated and is being .. (click here to read more)

Running CAW with Singularity and Nextflow

  • Maxime Garcia
  • 16 November 2017

This is a guest post authored by Maxime Garcia from the Science for Life Laboratory in Sweden. Max describes how they deploy complex cancer data analysis pipelines using Nextflow and Singularity. We are very happy to share their experience across the Nextflow community.

The CAW pipeline

Cancer Analysis Workflow logo

Cancer Analysis Workflow (CAW for short) is a Nextflow based analysis pipeline developed for the analysis of tumour: normal pairs. It is developed in collaboration with two infrastructures within Science for Life Laboratory: National Genomics Infrastructure (NGI), in The Stockholm Genomics Applications Development Facility to be precise and National Bioinformatics Infrastructure Sweden (NBIS).

CAW is based on GATK Best Practices for the preprocessing of FastQ files, then uses various variant calling tools to look for somatic SNVs and small indels (MuTect1, MuTect2, Strelka, Freebayes), (GATK HaplotyeCaller), for structural variants(click here to read more)

Scaling with AWS Batch

  • Paolo Di Tommaso
  • 08 November 2017

The latest Nextflow release (0.26.0) includes built-in support for AWS Batch, a managed computing service that allows the execution of containerised workloads over the Amazon EC2 Container Service (ECS).

This feature allows the seamless deployment of Nextflow pipelines in the cloud by offloading the process executions as managed Batch jobs. The service takes care to spin up the required computing instances on-demand, scaling up and down the number and composition of the instances to best accommodate the actual workload resource needs at any point in time.

AWS Batch shares with Nextflow the same vision regarding workflow containerisation i.e. each compute task is executed in its own Docker container. This dramatically simplifies the workflow deployment through the download of a few container images. This common design background made the support for AWS Batch a natural extension for Nextflow.

Batch in a nutshell

Batch is organised in Compute Environments, Job queues, Job definitions and .. (click here to read more)

Nexflow Hackathon 2017

  • Evan Floden
  • 30 September 2017

Last week saw the inaugural Nextflow meeting organised at the Centre for Genomic Regulation (CRG) in Barcelona. The event combined talks, demos, a tutorial/workshop for beginners as well as two hackathon sessions for more advanced users.

Nearly 50 participants attended over the two days which included an entertaining tapas course during the first evening!

One of the main objectives of the event was to bring together Nextflow users to work together on common interest projects. There were several proposals for the hackathon sessions and in the end five diverse ideas were chosen for communal development ranging from new pipelines through to the addition of new features in Nextflow.

The proposals and outcomes of each the projects, which can be found in the issues section of this GitHub repository, have been summarised below.

Nextflow HTML tracing reports

The HTML tracing project aims to generate a rendered version of the Nextflow trace file to .. (click here to read more)

Nextflow and the Common Workflow Language

  • Kevin Sayers
  • 20 July 2017

The Common Workflow Language (CWL) is a specification for defining workflows in a declarative manner. It has been implemented to varying degrees by different software packages. Nextflow and CWL share a common goal of enabling portable reproducible workflows.

We are currently investigating the automatic conversion of CWL workflows into Nextflow scripts to increase the portability of workflows. This work is being developed as the cwl2nxf project, currently in early prototype stage.

Our first phase of the project was to determine mappings of CWL to Nextflow and familiarize ourselves with how the current implementation of the converter supports a number of CWL specific features.

Mapping CWL to Nextflow

Inputs in the CWL workflow file are initially parsed as channels or other Nextflow input types. Each step specified in the workflow is then parsed independently. At the time of writing subworkflows are not supported, each step must be a CWL CommandLineTool .. (click here to read more)

Nextflow workshop is coming!

  • Paolo Di Tommaso
  • 26 April 2017

We are excited to announce the first Nextflow workshop that will take place at the Barcelona Biomedical Research Park building (PRBB) on 14-15th September 2017.

This event is open to everybody who is interested in the problem of computational workflow reproducibility. Leading experts and users will discuss the current .. (click here to read more)

Nextflow published in Nature Biotechnology

  • Paolo Di Tommaso
  • 12 April 2017

We are excited to announce the publication of our work Nextflow enables reproducible computational workflows in Nature Biotechnology.

The article provides a description of the fundamental components and principles of Nextflow. We illustrate how the unique combination of containers, pipeline sharing and portable deployment provides tangible advantages to researchers wishing to generate reproducible computational workflows.

Reproducibility is a major challenge in today's scientific environment. We show how three bioinformatics data analyses produce different results when executed on different execution platforms and how Nextflow, along with software containers, can be used to control numerical stability, enabling consistent and replicable results across different computing platforms. As complex omics analyses enter the clinical setting, ensuring that results remain stable brings on extra importance.

Since its first release three years ago, the Nextflow user base has grown in an organic fashion. From the beginning it has been our own demands in a workflow tool and .. (click here to read more)

More fun with containers in HPC

  • Paolo Di Tommaso
  • 20 December 2016

Nextflow was one of the first workflow framework to provide built-in support for Docker containers. A couple of years ago we also started to experiment with the deployment of containerised bioinformatic pipelines at CRG, using Docker technology (see here and here).

We found that by isolating and packaging the complete computational workflow environment with the use of Docker images, radically simplifies the burden of maintaining complex dependency graphs of real workload data analysis pipelines.

Even more importantly, the use of containers enables replicable results with minimal effort for the system configuration. The entire computational environment can be archived in a self-contained executable format, allowing the replication of the associated analysis at any point in time.

This ability is the main reason that drove the rapid adoption of Docker in the bioinformatic community and its support in many projects, like for example Galaxy, CWL, Bioboxes, Dockstore and .. (click here to read more)

Enabling elastic computing with Nextflow

  • Paolo Di Tommaso
  • 19 October 2016

Learn how to deploy an elastic computing cluster in the AWS cloud with Nextflow

In the previous post I introduced the new cloud native support for AWS provided by Nextflow.

It allows the creation of a computing cluster in the cloud in a no-brainer way, enabling the deployment of complex computational pipelines in a few commands.

This solution is characterised by using a lean application stack which does not require any third party component installed in the EC2 instances other than a Java VM and the Docker engine (the latter it's only required in order to deploy pipeline binary dependencies).

Nextflow cloud deployment

Each EC2 instance runs a script, at bootstrap time, that mounts the EFS storage and downloads and launches the Nextflow cluster daemon. This daemon is self-configuring, it automatically discovers the other running instances and .. (click here to read more)

Deploy your computational pipelines in the cloud at the snap-of-a-finger

  • Paolo Di Tommaso
  • 01 September 2016

Learn how to deploy and run a computational pipeline in the Amazon AWS cloud with ease thanks to Nextflow and Docker containers

Nextflow is a framework that simplifies the writing of parallel and distributed computational pipelines in a portable and reproducible manner across different computing platforms, from a laptop to a cluster of computers.

Indeed, the original idea, when this project started three years ago, was to implement a tool that would allow researchers in our lab to smoothly migrate their data analysis applications in the cloud when needed - without having to change or adapt their code.

However to date Nextflow has been used mostly to deploy computational workflows within on-premise computing clusters or HPC data-centers, because these infrastructures are easier to use and provide, on average, cheaper cost and better performance when compared to a cloud environment.

A major obstacle to .. (click here to read more)

Docker for dunces & Nextflow for nunces

  • Evan Floden
  • 10 June 2016

Below is a step-by-step guide for creating Docker images for use with Nextflow pipelines. This post was inspired by recent experiences and written with the hope that it may encourage others to join in the virtualization revolution.

Modern science is built on collaboration. Recently I became involved with one such venture between several groups across Europe. The aim was to annotate long non-coding RNA (lncRNA) in farm animals and I agreed to help with the annotation based on RNA-Seq data. The basic procedure relies on mapping short read data from many different tissues to a genome, generating transcripts and then determining if they are likely to be lncRNA or protein coding genes.

During several successful 'hackathon' meetings the best approach was decided and implemented in a joint effort. I undertook the task of wrapping the procedure up into a Nextflow pipeline with a view to replicating the results across our .. (click here to read more)

Workflows & publishing: best practice for reproducibility

  • Evan Floden
  • 13 April 2016

Publication time acts as a snapshot for scientific work. Whether a project is ongoing or not, work which was performed months ago must be described, new software documented, data collated and figures generated.

The monumental increase in data and pipeline complexity has led to this task being performed to many differing standards, or lack of thereof. We all agree it is not good enough to simply note down the software version number. But what practical measures can be taken?

The recent publication describing Kallisto (Bray et al. 2016) provides an excellent high profile example of the growing efforts to ensure reproducible science in computational biology. The authors provide a GitHub repository that “contains all the analysis to reproduce the results in the kallisto paper”.

They should be applauded and indeed - in the Twittersphere - they were. The corresponding author Lior Pachter stated that the publication could be .. (click here to read more)

Error recovery and automatic resource management with Nextflow

  • Paolo Di Tommaso
  • 11 February 2016

Recently a new feature has been added to Nextflow that allows failing jobs to be rescheduled, automatically increasing the amount of computational resources requested.

The problem

Nextflow provides a mechanism that allows tasks to be automatically re-executed when a command terminates with an error exit status. This is useful to handle errors caused by temporary or even permanent failures (i.e. network hiccups, broken disks, etc.) that may happen in a cloud based environment.

However in an HPC cluster these events are very rare. In this scenario error conditions are more likely to be caused by a peak in computing resources, allocated by a job exceeding the original resource requested. This leads to the batch scheduler killing the job which in turn stops the overall pipeline execution.

In this context automatically re-executing the failed task is useless because it would simply replicate the same error condition. A common solution consists of increasing .. (click here to read more)

Developing a bioinformatics pipeline across multiple environments

  • Evan Floden
  • 04 February 2016

As a new bioinformatics student with little formal computer science training, there are few things that scare me more than PhD committee meetings and having to run my code in a completely different operating environment.

Recently my work landed me in the middle of the phylogenetic tree jungle and the computational requirements of my project far outgrew the resources that were available on our institute’s Univa Grid Engine based cluster. Luckily for me, an opportunity arose to participate in a joint program at the MareNostrum HPC at the Barcelona Supercomputing Centre (BSC).

As one of the top 100 supercomputers in the world, the MareNostrum III dwarfs our cluster and consists of nearly 50'000 processors. However it soon became apparent that with great power comes great responsibility and in the case of the BSC, great restrictions. These include no internet access, restrictive wall times for jobs, longer queues, fewer .. (click here to read more)

MPI-like distributed execution with Nextflow

  • Paolo Di Tommaso
  • 13 November 2015

The main goal of Nextflow is to make workflows portable across different computing platforms taking advantage of the parallelisation features provided by the underlying system without having to reimplement your application code.

From the beginning Nextflow has included executors designed to target the most popular resource managers and batch schedulers commonly used in HPC data centers, such as Univa Grid Engine, Platform LSF, SLURM, PBS and Torque.

When using one of these executors Nextflow submits the computational workflow tasks as independent job requests to the underlying platform scheduler, specifying for each of them the computing resources needed to carry out its job.

This approach works well for workflows that are composed of long running tasks, which is the case of most common genomic pipelines.

However this approach does not scale well for workloads made up of a large number of short-lived tasks (e.g. a few seconds .. (click here to read more)

The impact of Docker containers on the performance of genomic pipelines

  • Paolo Di Tommaso
  • 15 June 2015

In a recent publication we assessed the impact of Docker containers technology on the performance of bioinformatic tools and data analysis workflows.

We benchmarked three different data analyses: a RNA sequence pipeline for gene expression, a consensus assembly and variant calling pipeline, and finally a pipeline for the detection and mapping of long non-coding RNAs.

We found that Docker containers have only a minor impact on the performance of common genomic data analysis, which is negligible when the executed tasks are demanding in terms of computational time.

This publication is available as PeerJ preprint at this link.

Innovation In Science - The story behind Nextflow

  • Maria Chatzou
  • 09 June 2015

Innovation can be viewed as the application of solutions that meet new requirements or existing market needs. Academia has traditionally been the driving force of innovation. Scientific ideas have shaped the world, but only a few of them were brought to market by the inventing scientists themselves, resulting in both time and financial loses.

Lately there have been several attempts to boost scientific innovation and translation, with most notable in Europe being the Horizon 2020 funding program. The problem with these types of funding is that they are not designed for PhDs and Postdocs, but rather aim to promote the collaboration of senior scientists in different institutions. This neglects two very important facts, first and foremost that most of the Nobel prizes were given for discoveries made when scientists were in their 20's / 30's (not in their 50's / 60's). Secondly, innovation really happens when a few individuals (not .. (click here to read more)

Introducing Nextflow REPL Console

  • Paolo Di Tommaso
  • 14 April 2015

The latest version of Nextflow introduces a new console graphical interface.

The Nextflow console is a REPL (read-eval-print loop) environment that allows one to quickly test part of a script or pieces of Nextflow code in an interactive manner.

It is a handy tool that allows one to evaluate fragments of Nextflow/Groovy code or fast prototype a complete pipeline script.

Getting started

The console application is included in the latest version of Nextflow (0.13.1 or higher).

You can try this feature out, having Nextflow installed on your computer, by entering the following command in your shell terminal: nextflow console.

When you execute it for the first time, Nextflow will spend a few seconds downloading the required runtime dependencies. When complete the console window will appear as shown in the picture below.

Nextflow console

It contains a text editor (the top white box) that .. (click here to read more)

Using Docker for scientific data analysis in an HPC cluster

  • Paolo Di Tommaso
  • 06 November 2014

Scientific data analysis pipelines are rarely composed by a single piece of software. In a real world scenario, computational pipelines are made up of multiple stages, each of which can execute many different scripts, system commands and external tools deployed in a hosting computing environment, usually an HPC cluster.

As I work as a research engineer in a bioinformatics lab I experience on a daily basis the difficulties related on keeping such a piece of software consistent.

Computing environments can change frequently in order to test new pieces of software or maybe because system libraries need to be updated. For this reason replicating the results of a data analysis over time can be a challenging task.

Docker has emerged recently as a new type of virtualisation technology that allows one to create a self-contained runtime environment. There are plenty of examples showing the benefits of using it to run .. (click here to read more)

Reproducibility in Science - Nextflow meets Docker

  • Maria Chatzou
  • 09 September 2014

The scientific world nowadays operates on the basis of published articles. These are used to report novel discoveries to the rest of the scientific community.

But have you ever wondered what a scientific article is? It is a:

  1. defeasible argument for claims, supported by
  2. exhibited, reproducible data and methods, and
  3. explicit references to other work in that domain;
  4. described using domain-agreed technical terminology,
  5. which exists within a complex ecosystem of technologies, people and activities.

Hence the very essence of Science relies on the ability of scientists to reproduce and build upon each other’s published results.

So how much can we rely on published data? In a recent report in Nature, researchers at the Amgen corporation found that only 11% of the academic research in the literature was reproducible by their groups [1].

While many factors are likely at play here, perhaps the most basic requirement for reproducibility holds that .. (click here to read more)

Share Nextflow pipelines with GitHub

  • Paolo Di Tommaso
  • 07 August 2014

The GitHub code repository and collaboration platform is widely used between researchers to publish their work and to collaborate on projects source code.

Even more interestingly a few months ago GitHub announced improved support for researchers making it possible to get a Digital Object Identifier (DOI) for any GitHub repository archive.

With a DOI for your GitHub repository archive your code becomes formally citable in scientific publications.

Why use GitHub with Nextflow?

The latest Nextflow release (0.9.0) seamlessly integrates with GitHub. This feature allows you to manage your code in a more consistent manner, or use other people's Nextflow pipelines, published through GitHub, in a quick and transparent manner.

How it works

The idea is very simple, when you launch a script execution with Nextflow, it will look for a file with the pipeline name you've specified. If that file does not exist, it will look for a public repository with .. (click here to read more)