OS for custom image in AWS Parallel Cluster

Question

when I create a parallel cluster, I am given the option to load a custom image. But when I do it, I still must give also an OS (chosen among Amazon, Ubuntu, Centos, RHEL). See snapshot.
Indeed, the resulting yaml contains the lines:

**Image:
  Os: rhel8
  CustomAmi: ami-06c363e70e31c99d6**

What are the implications of selecting an OS, if I have passed an image? I need to understand where that OS information is used exactly, also because my AMI is based on Rocky (which is not in the list). 
![Enter image description here](/media/postImages/original/IMYEvmR63yQ7eKct1DOnShhQ)

Abhishek_T · Answer

Hello,

The OS parameter is used by AWS ParallelCluster to determine the base operating system for the custom AMI. This information is required because AWS ParallelCluster needs to know the underlying operating system to configure certain aspects of the cluster setup and management, such as package managers, system utilities, and other OS-specific configurations.

Even though you provide a custom AMI, AWS ParallelCluster still needs to know the base operating system it is built upon. This is because the custom AMI you provide is likely derived from a base operating system provided by the cloud provider (e.g., Amazon Linux, Red Hat Enterprise Linux, or Ubuntu).

Additionally please note that PC supports Rocky: rocky8 and rocky9.

However I see you are using PCUI. Please note that PCUI wizard does not guarantee feature parity with PC for a while now. Therefore, you can select any OS and then manually set it to rocky8 or rocky9 at the end of the wizard.

Be rest assured, as we are already working on aligning OSes in the wizard to the ones supported by PC.

You can track the updates here:
[+] https://docs.aws.amazon.com/parallelcluster/latest/ug/document_history.html

OS for custom image in AWS Parallel Cluster

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