How to pass GitLab CI file variable to Dockerfile and docker container?

Question

GitLab CI allows adding custom variables to a project.

It allows to use a secret variable of type file where I specify a Key that is the variable name and Value that is the content of a file(e.g. content of certificate)

Then during execution of the pipeline the content will be saved as a temporary file and calling the variable name will return the path to the created file.

Ultimately I need to copy this file to a Docker container that is created when building the project. (docker build ... in the yml)

When testing if the variable works, I tried echo $VARIABLE in .gitlab-ci.yml and it works, returns path of temp file. But when doing RUN echo $VARIABLE in the Dockerfile, it is empty. Therefore I also cannot use ADD $VARIABLE /tmp/ which is my goal.

Is there a way to solve this and make this file available to the Dockerfile? I am new to Docker and GitLab and not sure where else to look.

Answer 1

Had to use .yml file docker build argument --build-arg VARIABLE and in Dockerfile use ARG VARIABLE so the Dockerfile knows it needs to use variable from environment.

Answer 2

Unfortunately, it's not possible like this because the file from CI/CD variable are copied at build time into a tmp directory ($CI_PROJECT_DIR.tmp) which is not in the docker build context. However, ADD need files present in the build context as documented

A workaround could be to copy the content of file in the current directory (supposing the Dockerfile is in ${CI_PROJECT_DIR}) before the docker build command :

cat $VARIABLE > ${CI_PROJECT_DIR}\mynewfile

and refer the the file in the Dockerfile :

ADD mynewfile /tmp/