Hi, is it possible to set env vars passed to docker using

build_arg

to have some default value. The use case is we set such env vars only in our CI/CD but for local run it can be any random value. https://www.pantsbuild.org/docs/tagging-docker-images#using-env-vars-to-include-dynamic-data-in-tags

It may be a bit tricky to get optional defaults, but if you provide a default value in your Dockerfile for the build arg, that should get picked up, if I remember correctly.

This is mostly about tagging the docker image using

build_args

in pants. Pants will complain currently

16:50:37.01 [ERROR] 1 Exception encountered:

  DockerBuildContextError: Undefined value for build arg on the src/pyfleet-charge-plan:charge_plan_image target: The Docker environment variable 'ECR_REPO_URI' is undefined. You may provide a value for this variable either in `[docker].env_vars` or in Pants's own environment.

If you did not intend to inherit the value for this build arg from the environment, provide a default value with the option `[docker].build_args` or in the `extra_build_args` field on the target definition. Alternatively, you may also provide a default value on the `ARG` instruction directly in the `Dockerfile`.

Oh look at that. It even mentioned the default in Dockerfile I was referring you to now.. 😆

My confusion is around tagging related args. The kind of build args which you are talking about is set inside the dockerfile. Will they also be available outside when tagging?

yes

This doesn’t work if I don’t export GIT_COMMIT and ECR_REPO_URI • Dockerfile

FROM public.ecr.aws/docker/library/python:3.9.13-slim-bullseye

ARG GIT_COMMIT '123'
ARG ECR_REPO_URI 'test.repo'

• pants.toml

[docker]
build_args = ["GIT_COMMIT", "ECR_REPO_URI"]

@curved-television-6568 Just checking there's no way to set a default for GIT_COMMIT when running locally? I guess can just tell other to set it in their env.

In recent versions of the

pants

script there’s an option to provide a

.pants.bootstrap

script that can setup local env vars for you before invoking pants (name is customizable): https://github.com/pantsbuild/setup/blob/ab8581bb52d92fcb3fda1b1dfb20204ae8888a90/pants#L19-L23 so you can have:

# .pants.bootstrap
: ${GIT_COMMIT:=$(git rev-parse HEAD)}

to set GIT_COMMIT if not already set.

Yes, that would work, thanks!

ok, cool 🙂