Amazon S3 storage

Nextflow includes the support for Amazon S3 storage. Files stored in a S3 bucket can be accessed transparently in your pipeline script like any other file in the local file system.

S3 path

In order to access a S3 file you only need to prefix the file path with the s3 schema and the bucket name where it is stored.

For example if you need to access the file /data/sequences.fa stored in a bucket with name my-bucket, that file can be accessed using the following fully qualified path:


The usual file operations can be applied on a path handle created using the above notation. For example the content of a S3 file can be printed as shown below:

println file('s3://my-bucket/data/sequences.fa').text

See section Files and I/O to learn more about available file operations.

Security credentials

Amazon access credentials can be provided in two ways:

  1. Using AWS access and secret keys in your pipeline configuration.
  2. Using IAM roles to grant access to S3 storage on Amazon EC2 instances.

AWS access and secret keys

The AWS access and secret keys can be specified by using the aws section in the nextflow.config configuration. file as shown below:

aws {
  accessKey = '<Your AWS access key>'
  secretKey = '<Your AWS secret key>'
  region = '<AWS region identifier>'

If the access credentials are not found in the above file, Nextflow looks for AWS credentials in a number of different places, including environment variables and local AWS configuration files.

Nextflow looks for AWS credentials in the following order:

  1. the nextflow.config file in the pipeline execution directory
  2. the environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY
  3. the environment variables AWS_ACCESS_KEY and AWS_SECRET_KEY
  4. the default profile in the AWS credentials file located at ~/.aws/credentials
  5. the default profile in the AWS client configuration file located at ~/.aws/config

More information regarding AWS Security Credentials are available in Amazon documentation.

IAM roles Amazon EC2 instances

When running your pipeline into a Ec2 instance, IAM roles can be used to grant access to AWS resources.

In this scenario, you only need to launch the Ec2 instance specifying a IAM role which includes a S3 full access policy. Nextflow will detected and acquire automatically the access grant to the S3 storage, without any further configuration.

Learn more about Using IAM Roles to Delegate Permissions to Applications that Run on Amazon EC2 on Amazon documentation.

Advanced configuration

Read AWS configuration section to learn more about advanced S3 client configuration options.