CODEWITHSUNDEEP
node.jsdockerdockerfile
Aero Wang
Aero Wang

Reputation: 9267

Set dynamic ENV in Dockerfile (and I can modify the Dockerfile only)

At work we are able to build image from Dockerfile and we do not have access to the docker command.

My goal is to be able to set environment variables based on my commit message or branch. Here is my try:

RUN branch=$(git branch | sed -n -e 's/^\* \(.*\)/\1/p' | awk -Frelease/ '/release/{print $2}') \
    && if [[ "$branch" != qa* ]]; then branch=$(git log -1 --pretty | grep release\/ | awk -Frelease/ '/release/{print $2}' | awk -F: '{print $1}'); fi

ENV EXPORT_ENV $branch

CMD ["npm", "run", "start"]

However, in my npm run start script it gets process.env.EXPORT_ENV as undefined.

Upvotes: 1

Views: 1294

Answers (1)

larsks
larsks

Reputation: 312610

On second thought, let me expand on my comment:

You can't set Dockerfile environment variables to the result of commands in a RUN statement. Variables set in a RUN statement are ephemeral; they exist only while the RUN statement is active

If you don't have access to the host environment (to pass arguments to the docker build command), you're not going to be able to do exactly what you want.

However, you can add an ENTRYPOINT script to your container that will set up dynamic environment variables before the main process runs. That is, if you have in your Dockerfile:

ENTRYPOINT ["/docker-entrypoint.sh"]

And in /docker-entrypoint.sh you have:

#!/bin/bash

branch=$(git branch | sed -n -e 's/^\* \(.*\)/\1/p' | awk -Frelease/ '/release/{print $2}') \
    && if [[ "$branch" != qa* ]]; then branch=$(git log -1 --pretty | grep release\/ | awk -Frelease/ '/release/{print $2}' | awk -F: '{print $1}'); fi)

export EXPORT_ENV="$branch"

exec "$@"

Then the EXPORT_ENV environment variable would be available in the environment of your CMD process.

Upvotes: 2

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