Support buffer limit option in FireLens

[zhonghui12]

Summary

Provide an entry to configurefluentd-buffer-limit in FireLens.
This is being enabled to resolve the following request: aws/containers-roadmap#964

Implementation details

Help to configure buffer limit size in fluentD Log Driver

Testing

• Updated two unit tests and manually tested the feature with make test
• The code also passed the end-to-end test on my instance.
  Here is my task definition file:

"logConfiguration": {
        "logDriver": "awsfirelens",
        "secretOptions": null,
        "options": {
          "log_group_name": "/aws/ecs/containerinsights/$(ecs_cluster)/application",
          "log-driver-buffer-limit": "123456",
          "auto_create_group": "true",
          "log_key": "log",
          "log_stream_prefix": "log_stream_name",
          "region": "us-west-2",
          "Name": "cloudwatch"
        }

Result for docker inspect:

"HostConfig": {
            "Binds": [],
            "ContainerIDFile": "",
            "LogConfig": {
                "Type": "fluentd",
                "Config": {
                    "fluentd-address": "unix:///var/lib/ecs/data/firelens/677a7f0ded6c47709e26665f714e4c76/socket/fluent.sock",
                    "fluentd-async-connect": "true",
                    "fluentd-buffer-limit": "123456",
                    "fluentd-sub-second-precision": "true",
                    "tag": "app-firelens-677a7f0ded6c47709e26665f714e4c76"
                }
            },

Also, tested it with no log-driver-buffer-limit option:

"HostConfig": {
            "Binds": [],
            "ContainerIDFile": "",
            "LogConfig": {
                "Type": "fluentd",
                "Config": {
                    "fluentd-address": "unix:///var/lib/ecs/data/firelens/65b06118b2014ccd9ef92abf5727577d/socket/fluent.sock",
                    "fluentd-async-connect": "true",
                    "fluentd-sub-second-precision": "true",
                    "tag": "app-firelens-65b06118b2014ccd9ef92abf5727577d" 
                }
            },

Description for the changelog

Feature FluentD: Support for buffer limit size configuration.

Licensing

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

[PettitWesley]

I'm confused, this suggested its a field on the task structure, but then in the other file I don't see it added as a field in that struct...

[zhonghui12]

I learnt from this PR that just adding one field here is enough: https://github.com/aws/amazon-ecs-agent/pull/2538/files#diff-0f6cc891620e98230e92868ea887af5e1f11d9e692fc8415a50c1dd0b130cc8cR1106

[zhonghui12]

It is not a field on the task structure, it is a field in Config. And we need to get the value from the task package

[PettitWesley]

Okay, but our requirement is that each container can have its own log driver buffer setting. So I think it needs to be stored somewhere which is both per-task and per-container. Not some global setting.

[fenxiong]

i don't think this needs to be saved anywhere. instead just do the following should work: (1) in collectFirelensLogOptions, skip adding the option to containerToLogOptions if the key equals firelensLogDriverBufferLimitOption; (2) here, get the actual value for "fluentd-buffer-limit" from the container's log config before we reset it at the previous line logConfig.Config = make(map[string]string), and then save it to the config here.

[zhonghui12]

@PettitWesley @fenxiong updated the code and already tested it in my local by make test

[fenxiong]

this should only be added when bufferLimit is not empty

[zhonghui12]

I see here has a check for empty string so I didn't add it: https://github.com/moby/moby/blob/master/daemon/logger/fluentd/fluentd.go#L174. But yeah, we should handle this case here. Thanks for the suggestion.

[zhonghui12]

Update the PR based on the comments. Will squash all commits into one if PR is approved

[fenxiong]

static check is failing for other reason and has been fixed in 997c975. please rebase on latest dev branch to get the tests passed