Gitlab CI/CD fails to build docker image

I have built a custom base image from alpine and use it as the base for ruby services that we develop.

FROM ruby:2.4.2-alpine
...

I use Gitlab and Gitlab's docker registry along with it. Each project has its own docker image storage.

I created a separate project for the alpine-ruby-service dockerfile. Then build and pushed the image to Gitlab.

In the ruby service project docker images, I reference it as follows

FROM gitlab.mycompany.dk/alpine-ruby-service-base
...

I have a CI/CD pipeline (.gitlab-ci.yaml) which builds these ruby service images when there is a commit to one of the branches.

The problem is that when the CI/CD pipeline is run it fails with the following message

$ docker build --pull -t $CONTAINER_TEST_IMAGE .
   Sending build context to Docker daemon  709.6kB

 Step 1/13 : FROM gitlab.mycompany.dk:xxxx/alpine-ruby-service-base
 pull access denied for gitlab.mycompany.dk:xxxx/alpine-ruby-service-base,
 repository does not exist or may require 'docker login': denied: 
 requested access to the resource is denied

I have an instruction to login to the Gitlab docker registry before the build command above using

docker login --username=gitlab-ci-token --password=$CI_JOB_TOKEN gitlab.mycompany.dk:xxxx

the login succeeds but the following docker build instruction fails!!! can someone point me what is going wrong?

It looks like that the docker login and the docker build were done by different users. If a docker login is performed, then a ~/.docker directory will be created in the namespace of user X, if the build is done by user Y then the latter user does not have a .docker folder and is not authorized to pull the image. One could verify this by echo $USER in the pipeline, in this case gitlab-ci.yaml to check this.

StackExchange DevOps Q#8823, answer score: 2