Pass docker_image to COPY --from statement

[jake-normal]

I am looking for a way to pass a previous docker build stage into the --from field of a docker COPY statement. Something like this:

docker_image(
    name="deps",
    ...
)

docker_image(
    ...
    instructions=[
        ...
        "COPY --from=:deps /bin/app /bin/app",
        ...
    ],
)

where :deps in --from=:deps references the previous deps stage.

Unfortunately, this doesn't seem to work right now.

Any tips / workarounds?

[cburroughs]

Try the recipes at: https://www.pantsbuild.org/blog/2022/08/02/optimizing-python-docker-deploys-using-pants

[jake-normal]

Thanks! I was eventually able to resolve this by:

1. Following the pattern above
2. Configuring a pants.toml like so:

[docker.registries.company-name]
# Address of local container registry for testing purposes
# See https://hub.docker.com/_/registry for more info
address = "localhost:5001"
default = true
use_local_alias = true

3. Configuring a pants.ci.toml like so:

[docker.registries.company-name]
address = "xxxxxxxxxxxx.dkr.ecr.us-east-1.amazonaws.com"
default = true

This allows me to run pants package :: and pants publish :: locally, pushing to a local registry for testing purposes, and run them in CI against my real registry when necessary.

[kaos]

Thanks for following up with your findings. 👍🏽

I'll post an alternative in case two docker_image targets are required, for whatever reason.

docker_image(name="deps")
docker_image(
  instructions=[
    "ARG DEPS=:deps",
    "FROM $DEPS AS deps",
    "FROM some/base/image",
    "COPY --from=deps ...",
  ]
)