Consume full task sync ACS responders from ecs-agent/

[danehlim]

Summary

Consume the task manifest responder and task stop verification ACK responder defined in ecs-agent module. These ACS message responders are used to support the full task sync feature.

Implementation details

Please note that, in the context of this PR, "ACS message responder"/"responder" is more or less synonymous with "ACS message handler"/"handler".

• Create new file agent/acs/handler/task_manifest_responder.go and inside that file, implement TaskComparer and SequenceNumberAccessor interfaces defined in ecs-agent module. Some parts of the implementation are based off of functionality that exists in the current agent/acs/handler/task_manifest_handler.go file
• Create new file agent/acs/handler/task_stop_verification_ack_responder.go and inside that file, implement TaskStopper interface defined in ecs-agent module. Some parts of the implementation are based off of functionality that exists in the current agent/acs/handler/task_manifest_handler.go file
• Add tests for the above in new files agent/acs/handler/task_manifest_responder_test.go and agent/acs/handler/task_stop_verification_ack_responder_test.go. Some tests are based off of tests that exist in the current agent/acs/handler/task_manifest_handler_test.go file
• Delete agent/acs/handler/task_manifest_handler.go and agent/acs/handler/task_manifest_handler_test.go
• In agent/acs/handler/acs_handler.go:
  • Initialize task manifest responder and add its HandlerFunc function as a request handler to the ACS client, such that task manifest responder dictates what to do in response to receiving task manifest messages from ACS
  • Initialize task stop verification ACK responder and add its HandlerFunc function as a request handler to the ACS client, such that task stop verification ACK responder dictates what to do in response to receiving task stop verification ACKs from ACS
    • NOTE: On L274, you will notice we are passing nil as the respond function parameter. This is because although the task stop verification ACK responder in ecs-agent module currently takes in and contains a respond function parameter, it actually doesn't use it since we do not send anything back to ACS in response to task stop verification ACKs. I've left removing this non-necessity from the task stop verification ACK responder in the ecs-agent module out of scope of this pull request as this pull request is limited to and focuses on changes in the agent module
  • Remove ACS messages related to full task sync feature from pending ACKs logic since it is no longer applicable/used after consuming the task manifest and task stop verification ACK responders from ecs-agent module
    • Such logic is no longer applicable since there is no need to do multi-thread synchronization with channels with this responder (like we currently do in agent/acs/handler/task_manifest_handler.go) and the responders in the ecs-agent module factor out this non-necessity and are a lot cleaner and simpler to follow.
      For reference see the following PR for a similar change previously made to the heartbeat responder for the same reason: Fix flakey leak test for ACS Handler #3232
  • Remove pending ACKs logic altogether since there are no longer any responders that use it now

Testing

Unit, integration, and functional tests.

New tests cover the changes: yes

Description for the changelog

Consume full task sync ACS responders from ecs-agent/

Licensing

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