[Suggestion] Add warning that pid_mode = task may conflict with exec ability

[dmrwebdev]

Appears that pid_mode is set to task by default which potentially can break the ability to exec into application containers when using this module (as it did ours). This led to a couple days of debugging until I discovered the issue described here and resolved by manually setting the pid_mode to null.

As there was no mention of this in any of the datadog documentation figured it might save people some time to have a quick note about it!

[gabedos]

Hey @dmrwebdev thanks for reaching out about this edge case with pidModes in ECS task definitions.

It's very odd that setting the value explicitly to task results in a different behavior than setting it to null because the only valid value for pid_mode in ECS Fargate is task. I've checked with our teams and for process collection to properly work on the Agent it requires the pidMode being explicitly set to task so I will add a note that notifies users about the impact this could have with exec abilities to other application containers.

It unfortunately looks like AWS ECS hasn't been able to prioritize fixing this bug for a while aws/containers-roadmap#2268

Sorry for any confusion this may have caused!