fix(ecs): require task pidMode for Linux-based Fargate tasks, not host

[CharlesHolmes]

Issue # (if applicable)

Closes #29995.

Reason for this change

Only the task option is allowed for pidMode on Linux-based Fargate tasks.

Description of changes

This PR builds on the changes introduced in #29670 but fixes the handling of pidMode so that it matches the behavior allowed by CloudFormation and described in the AWS User Guide.

Description of how you validated changes

Updated the existing tests so that task is the only allowable pidMode setting if a Fargate task's OS is Linux-based.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[victorwrotethis]

Appreciate the fix. I see you also added a check for it being a linux os family, which makes sense being the alternative already being present for denying pidmode usage. Though that does change the behavior, where it will now only warn when you set an OS family, I think that is a good thing as it's more consistent to only message on knowns.

It does however mean that without an os family you have to will wait until deployment to notice your mistake. If we want a synth level protection, then it would be better to also lock pidmode behind having set an os family. Your current changes mean that if you set PidMode.HOST on a non os family tagged resource, it will synth but fail on deployment. (And I guess if any are used on windows one)

[CharlesHolmes]

If we want a synth level protection, then it would be better to also lock pidmode behind having set an os family.

I like this because it only affects people who are already using the L2 pidMode (which was introduced only a few days ago) and only if they're not specifying an OS family. I'll put together the change.

Edit - In fact, because the existing pidMode functionality will fail on deployment (because host isn't allowed on Linux Fargate tasks), this shouldn't have any impact on existing code.

[xazhao]

Agree that it's not a breaking change because the deployment would fail with wrong pidMode value before. Left some nit comments

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• Commit ID: 0b85a60
• Result: SUCCEEDED
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