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All the Things I SHOULD Know

Unsoreted Tips Regarding Dockerfiles

Dockerfile Tips

Not every ARG is created equal

When using ARG in a Dockerfile, it is important to note that not every ARG has the same meaning. There are two types of ARG:

  1. Build-time ARGs: These are used during the build process and are not available in the final image.
  2. Run-time ARGs: These are used when the container is started and are available in the final image.

Here is an example of how to use both types:

# Build-time ARG
ARG BUILD_VERSION=latest
FROM alpine:${BUILD_VERSION}


# Run-time ARG
ARG RUN_VERSION=latest
CMD echo "Running version: ${RUN_VERSION}"

Note that in the example above, the BUILD_VERSION is only available to the FROM instruction, while the RUN_VERSION is available to the CMD instruction. Trying to use BUILD_VERSION in the CMD instruction will result in nonsense, since its value is not set at runtime and will therefore be empty.