Add function for docker compose to return stdout

[rhoboat]

What else does this PR need?

Purpose: I've just added a function that lets docker compose return only stdout, so that TLS Scripts followups can get just the Certificate ARN from stdout and clean up the resource during the test cleanup stage.

[yorinasub17]

Had some comments for improving the implementation slightly.

The one other thing to add is a unit or integration test for this function. You should be able to reuse the test for RunDockerCompose for this purpose (https://github.com/gruntwork-io/terratest/blob/master/test/packer_docker_example_test.go)

[rhoboat]

@yorinasub17 This test is failing, added in this commit, because the stdout actually includes a lot more stuff than I expect. The stdout should only contain "stdout: message", but it contains all of this:

Error:      	"Attaching to testdockercomposestdoutexample_bash_script_1
        	bash_script_1  | stderr: error
        	bash_script_1  | stdout: message
        	testdockercomposestdoutexample_bash_script_1 exited with code 0
        	" should not contain "stderr: error"

[yorinasub17]

The stdout should only contain "stdout: message", but it contains all of this:

Ahhhh this might not be possible then... Frustratingly, I can't find the docs on where they output the logs to. Let me try a few things to see if I can empirically validate.

[yorinasub17]

Ok yea both docker-compose and docker logs streams all the log output to STDOUT, including STDERR! This is especially frustrating considering that the logs are actually tracking the source (https://docs.docker.com/config/containers/logging/json-file/).

So it looks like this approach and function is not going to work 😞

[yorinasub17]

We probably need to add a function that extracts the stdout and stderr logs using the raw log files. I found the command that gives you the path to the raw log file which has the metadata on where it came from

docker inspect --format='{{.LogPath}}' DOCKER_IMAGE_ID

But... this is only accessible from the VM on mac osx so you can't actually see it directly and we'd need to yak shave a way to get into the VM...

[rhoboat]

@yorinasub17 However, when I source this change here locally in the TLS script, it's able to pull just the right info that's echoed to stdout, meaning the ARN. I was trying to figure out what the difference would be. Any ideas why it would work when used in service catalog but not here?

[rhoboat]

Ah, I solved the problem. If I call the bash_script with docker-compose run bash_script rather than up, it works.

[rhoboat]

🎉 Thanks @brikis98 and @yorinasub17! Ready for (final?) review.

[yorinasub17]

Updates LGTM (assuming build passes)! Found one more nit where we should expose another function, but we can punt that to another PR to avoid another test cycle.

[yorinasub17]

Just realized that we should probably expose a RunDockerComposeAndGetStdOutE function as well.

[rhoboat]

Thanks for the review! Failures are not related to this change, so merging.

[yorinasub17]

Don't forget to cut a new release!

[rhoboat]

Okay! Thanks for that. I was waiting for feedback on this! Will go ahead now.

[rhoboat]

Ah, before I do, did you see my comment in Slack? I wanted to make sure we were safe to do it, i.e. passing tests on the main branch. There were a few small failures in this branch but I merged because they were unrelated to this change. That's a bit of risky logic, though, and not how I'd normally like to do things. So my idea was to wait for green on master before cutting a release.