TLDR:

Build-time: FROM, LABEL, ARG, COPY, ADD, RUN, ONBUILD

Runtime: EXPOSE, CMD, ENTRYPOINT, VOLUME, HEALTHCHECK

Both: USER, WORKDIR, ENV

This has always been popping up when I'm working with Dockerfile or Docker compose. Some of the commands can be run in build-time, but some can't. Maybe you want to run a specific command only in runtime. Totally depends on your situation 🥂. On my end, this issue showed up in my prisma migration, quite similar to this github issue where I can't run prisma migrate on RUN instruction.

I'll be listing the things that I know currently is under Build-time, and Runtime.

🏗️ Build-time

These will run while the image is building (some came from this reference).

Instruction	Description
FROM	Specifies the base image.
LABEL	Adds metadata
ARG	Defines a build-time variable
COPY	Copies new files or directories from <src> and adds them to the filesystem of the container at the path <dest>.
ADD	Copies new files, directories or remote file URLs from <src> and adds them to the filesystem of the container at the path <dest>.
RUN	Executes any commands in a new layer on top of the current image and commits the results.
ONBUILD	Executes instructions when the image is used as a base image

🏃 Runtime

These will run when the image has been built, and the container will run.

Instruction	Description
EXPOSE	Documents the port the container listens on
CMD	Provides defaults for an executing container. These can include an executable, or they can omit the executable, in which case you must specify an ENTRYPOINT instruction.
ENTRYPOINT	Allows you to configure a container that will run as an executable.
VOLUME	Creates a mount point for persistent storage (ensures data is not lost when the container stops).
HEALTHCHECK	Defines a command to monitor the container’s health while it is running.

🫶 Both

These are being used for both Build-time, and Runtime.

Instruction	Description
USER	Sets the user for subsequent commands in buildtime, and sets the user for runtime CMD, and ENTRYPOINT
WORKDIR	Sets the working directory for any RUN, CMD, ENTRYPOINT, COPY and ADD instructions that follow in the Dockerfile.
ENV	Defines environment variables that are available both at build-time and runtime.

📖 Note

When using Docker compose, env is actually runtime. If you want to use it for build-time, use build arg instead.

That's it! 🔥