[exporter/datadog] Compatibility with ECS Fargate semantic conventions

[mx-psi]

Description:

This adds compatibility with AWS ECS Fargate OpenTelemetry semantic conventions by

• making the hostname empty for metrics that have a Fargate launchtype,
• reverting [exporter/datadogexporter] Always add current hostname #5967 so that running metrics don't report the Fargate host and
• adding the task_arn to running metrics so that users can see which tasks are running the exporter.

Previously, we already added task_arn automatically to tags/metadata; this is kept.

Users of Fargate versions that don't have TMDE v4 or later, need to add the aws.ecs.launchtype semantic convention manually to payloads, e.g. by means of the resource attribute:

processors:
  resource:
    attributes:
    - key: aws.ecs.launchtype
      value: fargate
      action: upsert

Link to tracking Issue: n/a, customer request

Testing: Added unit tests, tested end to end by mocking:

Resource processor configuration for mocking AWS ECS Fargate

processors:
  resource:
    attributes:
    - key: aws.ecs.launchtype
      value: fargate
      action: upsert
    - key: aws.ecs.task.arn
      value: "example-task-arn"
      action: upsert

[boostchicken]

Just a note, I have a absolutely had use cases in large Fargate clusters where one or two hosts went bad and the only way we caught it in DD was with hostname / ip based metrics we were gathering. This was a cluster of a few thousand tasks so a full re-deployment was out of the question.

[mx-psi]

I have a absolutely had use cases in large Fargate clusters where one or two hosts went bad and the only way we caught it in DD was with hostname / ip based metrics we were gathering

It's useful to know this, thanks! Here I am trying to do a reduced version of what the Datadog Agent does when setting the ECS_FARGATE environment variable, where the hostname is removed and provided info is task ARN based instead.

As it happens with the Datadog Agent, you can still get the hostname if you want: only if you use the resourcedetection processor's ecs detector will we remove the hostname. I think this will enable us to support both users that want the hostnames and users who don't (but if you think this won't work for some reason please let me know :)) ).

[KSerrania]

Left a comment but LGTM overall

[mx-psi]

@jpkrohling this has been approved by a CODEOWNER. If you find the time today, could you review and, if it looks good, merge it? Thanks!

[jpkrohling]

LGTM, just wanted to double-check a specific conditional.