(3.13.2 and earlier) Cluster and AMI creation will fail due to Python 3.9 Lambda runtime deprecation

The issue

Starting Aug 31, 2026, AWS Lambda will prevent creation of new Lambda functions using the Python 3.9 runtime. This affects ParallelCluster's ability to create clusters and custom AMIs because these operations rely on Lambda functions that run the custom resources defined in the cluster and build image CloudFormation stacks.

Users attempting to create clusters or build images after Aug 31, 2026 will encounter CloudFormation stack deployment failures due to the inability to deploy the underlying Lambda functions. Existing clusters will continue to operate normally.

See official documentation for further details about Lambda runtime deprecations.

Affected ParallelCluster versions, OSes and schedulers

ParallelCluster < 3.14.0.

Mitigation

This mitigation only applies to the ParallelCluster CLI. For ParallelCluster API, PCUI and custom resource users, upgrade to ParallelCluster 3.14.0 or later.

Install the ParallelCluster CLI from a patched commit to continue using affected versions. The patches upgrade the Lambda function runtime from Python 3.9 to Python 3.12, allowing the cluster and build image stacks to deploy successfully with the newer runtime version.

Version	Patch
3.13.0	https://github.com/aws/aws-parallelcluster/commit/185d2be36278d24d64ac9dff4b2bb96a8240b9ec
3.13.1	https://github.com/aws/aws-parallelcluster/commit/fd7673ccebfa1b3354e529db2bd0254fefd6f8a9
3.13.2	https://github.com/aws/aws-parallelcluster/commit/3fa694f1b719297fbbc20d8dc704fe9edcc7cc37

Example to apply the patch for version 3.13.2:

pip install "git+https://github.com/aws/aws-parallelcluster.git@3fa694f1b719297fbbc20d8dc704fe9edcc7cc37#subdirectory=cli"

The same command with the respective commit applies to the other versions.