The `--target` option doesn't seem to exist

[viraptor]

I think there was a mistake where the target option was added to the plugin. Specifically in https://github.com/buildkite-plugins/docker-compose-buildkite-plugin/issues/231 the referenced documentation is https://docs.docker.com/build/building/multi-stage/#stop-at-a-specific-build-stage

That option is specific to docker build though, not docker-compose build. If I understand the original request correctly, the way to do this in the plugin would be to add the option to the override yml instead.

Currently the plugin tries to add --target ... to the docker-compose build command and fails because it's not implemented https://docs.docker.com/engine/reference/commandline/compose_build/

(Unless this is some version specific behaviour that was added/removed in the meantime)

[toote]

@viraptor You are correct, thanks for pointing out! It was my fault as it was one of the first changes I did in this repository without completely understanding the code's and compose nuances.

While I want to correct the option, I am really interested in your expectations on how it should work and what kind of configurations you want off it. Also, I am not 100% sure how specifying a target would work when you are building multiple services. Do you have any thoughts on that?

[viraptor]

I am really interested in your expectations on how it should work and what kind of configurations you want off it.

My original use case was to have a service app pointing at a Dockerfile with multiple stages. Then the test steps would use an override to use target: ci which includes the test tools, while other steps would use the default which builds just the deployable image.

Turns out I had more differences to implement, so ended up just duplicating the service as ...-prod and ...-test in the docker-compose itself and assigning different targets there.

I think the option could still be useful in a simpler setup.

Also, I am not 100% sure how specifying a target would work when you are building multiple services. Do you have any thoughts on that?

Nope, I suspect it would have to be a hack for a single service only.

[camallen]

I just ran into this issue and assumed that specifying the target option would override the compose file to add a target build directive to the overridden service definition, thus allowing me to target a stage in a multi stage build.

Sadly this just slaps an incorrect --target onto the docker compose cmd which results in

$ docker-compose -f docker-compose.yml -p buildkite018c900423954192bc6a0b21321ae8ae -f docker-compose.buildkite-10-override.yml build --pull --target base app
unknown flag: --target
🚨 Error: The command exited with status 16

FWIW - My use case is similar to @viraptor in that i want to target a multi stage build.

https://github.com/buildkite-plugins/docker-compose-buildkite-plugin/issues/231#issuecomment-550067960 provides a similar use case I have where i'd like to prebuild multi stage cache images to avoid extra work in subsequent builds.