Refactor ACS refresh credentials message handling

[danehlim]

Summary

Refactor ACS refresh credentials message handling, update other associated code, and improve/update tests.

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".

1. Refactor ACS refresh credentials message handling
   • agent/acs/handler/refresh_credentials_handler.go -> ecs-agent/acs/session/refresh_credentials_responder.go (partial)
     • All components of the responder that do not directly interact with Agent state belong in this file
     • Refactor refreshCredentialsHandler struct and existing code into refreshCredentialsResponder struct, such that refreshCredentialsResponder struct implements the wsclient.RequestResponder interface
     • Move validation of the refresh credentials message's role type to the validateIAMRoleCredentialsMessage function
     • Use github.com/aws/amazon-ecs-agent/ecs-agent/logger instead of github.com/cihub/seelog for logging
     • Add support for publishing of metrics in various credentials refresh failure/success cases
       • NOTE: Our Agent defined in agent/ directory does not support metrics publishing, thus in agent/acs/handler/acs_handler.go our agent will supply the refresh credentials responder with a metrics.NewNopEntryFactory(), which is a no-op implementation of metrics publishing
   • agent/acs/handler/refresh_credentials_handler.go -> agent/acs/handler/refresh_credentials_responder.go (partial)
     • Components that interact with Agent state belong in this file
     • Refactor functionality from such components mentioned above into credentialsMetadataSetter struct such that credentialsMetadataSetter struct implements the CredentialsMetadataSetter interface defined in ecs-agent/acs/session/refresh_credentials_responder.go
   • agent/acs/handler/refresh_credentials_handler_linux.go -> agent/acs/handler/refresh_credentials_responder_linux.go (file renamed)
   • agent/acs/handler/refresh_credentials_handler_windows.go -> agent/acs/handler/refresh_credentials_responder_windows.go (file renamed)
2. Update other associated files
   • agent/acs/handler/acs_handler.go
     • Initialize refresh credentials responder and add its HandlerFunc function as a request handler to the ACS client, such that refresh credentials responder dictates what to do in response to receiving refresh credentials messages from ACS
     • Remove refresh credentials messages from pending ACKs logic since it is no longer applicable after the refactor of ACS refresh credentials message handling
       • 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). As part of the refactor, we factor out this non-necessity and thus methods such as start(), stop(), clearAcks(), etc. can be removed. The resulting responder is 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
   • agent/acs/handler/payload_handler.go
     • Don't pass in the entire refresh credentials responder to the payload responder as it is only being passed in to send ACKs of credentials associated with task(s) back to ACS. Instead, just write a private payload responder method makeCredentialsAckRequest and use it to accomplish the same while avoiding passing in a whole entire responder to another responder
       • For context, sending ACKs of credentials in the payload responder is necessary because payload responder handles credentials that are associated with task(s) contained in a payload message (type ecsacs.PayloadMessage). In contrast, refresh credentials responder handles credentials that are contained in a refresh credentials message (type ecsacs.IAMRoleCredentialsMessage)
   • ecs-agent/acs/session/generate_mocks.go and ecs-agent/acs/session/mocks/session_mock.go
     • Generate new mocks for the CredentialsMetadataSetter interface to be used in testing
   • ecs-agent/metrics/constants.go
     • Add constants specific to refresh credentials responder
3. Improve/update tests, most notably:
   • Update existing tests accordingly based off of above changes to refactor ACS refresh credentials message handling in the following files:
     • agent/acs/handler/refresh_credentials_handler_test.go -> ecs-agent/acs/session/refresh_credentials_responder_test.go (partial)
       • Refresh credentials responder tests that only need to interact with stateless components (e.g., message validation) belong in this file
     • agent/acs/handler/refresh_credentials_handler_test.go -> agent/acs/handler/refresh_credentials_responder_test.go (partial)
       • Refresh credentials responder tests that need to directly interact with Agent state belong in this file
     • agent/acs/handler/acs_handler_test.go
   • Update existing tests in agent/acs/handler/payload_handler_test.go accordingly based off of above changes to agent/acs/handler/payload_handler.go
   • General cleanup/quality of life updates to tests (e.g., use assert package for test assertions instead of if statement blocks)
   • Replace usage of test constants currently defined in agent/acs/handler/refresh_credentials_handler_test.go with test constants defined in centralized file ecs-agent/acs/session/testconst/test_const.go instead.
     • This results in changes to the following non-refresh credentials responder test files:
       • agent/acs/handler/attach_eni_handler_common_test.go
       • agent/acs/handler/payload_handler_test.go
       • agent/acs/handler/task_manifest_handler_test.go

Testing

Unit, integration, and functional tests.

New tests cover the changes: yes

Description for the changelog

Refactor ACS refresh credentials message handling

Licensing

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