Building a Custom AWS ParallelCluster AMI - AWS ParallelCluster

Building a Custom AWS ParallelCluster AMI


We don't recommend building a custom AMI as an approach for customizing AWS ParallelCluster.

This is because, after you build your own AMI, you no longer receive updates or bug fixes with future releases of AWS ParallelCluster. Moreover, if you build a custom AMI, you must repeat the steps that you used to create your custom AMI with each new AWS ParallelCluster release.

Before reading any further, we recommend that you first check out the Custom Bootstrap Actions section to determine if the modifications you want to make can be scripted and supported with future AWS ParallelCluster releases.

Even though building a custom AMI isn't ideal (because of the reasons mentioned earlier), there are still scenarios where building a custom AMI for AWS ParallelCluster is necessary. This tutorial guides you through the process of building a custom AMI for these scenarios.


Starting with AWS ParallelCluster version 2.6.1, most of the install recipes are skipped by default when launching nodes. This is to improve startup times. To run all of the install recipes for better backwards compatibility at the expense of startup times, add "skip_install_recipes" : "no" to the cluster key in the extra_json setting. For example:

extra_json = { "cluster" : { "skip_install_recipes" : "no" } }


How to Customize the AWS ParallelCluster AMI

There are three ways to use a custom AWS ParallelCluster AMI. Two of these three methods require you to build a new AMI that's available under your AWS account. The third method (Use a Custom AMI at Runtime) doesn't require that you build anything in advance. Choose the method that best fits your needs.

Modify an AWS ParallelCluster AMI

This is the safest and most recommended method. Because the base AWS ParallelCluster AMI is often updated with new releases, this AMI has all of the components required for AWS ParallelCluster to function when it's installed and configured. You can start with this as the base.

  1. In the AMI list, find the AMI that corresponds to the specific Region that you use. The AMI list that you choose must match the version of AWS ParallelCluster that you use. Run pcluster version to verify the version. For AWS ParallelCluster version 2.11.7, go to To select another version, use the same link, choose the Tag: 2.11.7 button, select the Tags tab, and then select the appropriate version.

  2. Within the Amazon EC2 console, choose Launch Instance.

  3. Navigate to Community AMIs, and enter the AMI ID for your Region into the search box.

  4. Select the AMI, choose your instance type and properties, and launch your instance.

  5. Log into your instance using the OS user and your SSH key.

  6. Customize your instance as required.

  7. Run the following command to prepare your instance for AMI creation:

    sudo /usr/local/sbin/
  8. Stop the instance.

  9. Create a new AMI from the instance.

  10. Enter the AMI id in the custom_ami field within your cluster configuration.

Build a Custom AWS ParallelCluster AMI

If you have a customized AMI and software already in place, you can apply the changes needed by AWS ParallelCluster on top of it.

  1. Install the following in your local system, together with the AWS ParallelCluster CLI:

    • Packer: find the latest version for your OS from the Packer website, and install it. The version must be at least 1.4.0, but the latest version is recommended. Verify that the packer command is available in your PATH.


    Before AWS ParallelCluster version 2.8.0, Berkshelf (which is installed by using gem install berkshelf) was required to use pcluster createami.

  2. Configure your AWS account credentials so that Packer can make calls to AWS API operations on your behalf. The minimal set of required permissions necessary for Packer to work are documented in the IAM Task or Instance Role section of the Amazon AMI Builder topic in the Packer documentation.

  3. Use the command createami in the AWS ParallelCluster CLI to build an AWS ParallelCluster AMI starting from the one that you provide as base:

    pcluster createami --ami-id <BASE_AMI> --os <BASE_AMI_OS>

    You shouldn't use an AWS ParallelCluster AMI from a running cluster as <BASE_AMI> for the createami command. Otherwise, the command fails.

    For other parameters, see pcluster createami.

  4. The command in Step 4 runs Packer, which specifically does the following:

    1. Launches an instance using the base AMI provided.

    2. Applies the AWS ParallelCluster cookbook to the instance to install relevant software and perform other necessary configuration tasks.

    3. Stops the instance.

    4. Creates an new AMI from the instance.

    5. Terminates the instance after the AMI is created.

    6. Outputs the new AMI ID string to use to create your cluster.

  5. To create your cluster, enter the AMI ID in the custom_ami field within your cluster configuration.


The instance type used to build a custom AWS ParallelCluster AMI is t2.xlarge. This instance type doesn't qualify for the AWS free tier, so you're charged for any instances that are created when you build this AMI.

Use a Custom AMI at Runtime

If you don't want to create anything in advance, you can use your AMI and create an AWS ParallelCluster from that AMI.

With this method, it takes longer for the AWS ParallelCluster to be created because all the software that's needed by AWS ParallelCluster when the cluster is created must be installed. Moreover, scaling up also takes a longer time.

  • Enter the AMI id in the custom_ami field within your cluster configuration.