DIND Service fails (no such host error) when using dependency proxy

GitLab CI/CD
1

Version: Gitlab.com with local (EC2-based) runners

Problem:
I’ve hit an odd error where my dind-based docker builds fail when using an image pulled from the dependency proxy (CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX), but run correctly when pulling the image directly from docker.
The configuration pasted below fails with the error “error during connect: Post http://docker:2375/v1.40/auth: dial tcp: lookup docker on :53:no such host”. However, if I change the services: name entry to “docker:19.03.12-dind”; i.e., I remove the “CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX” portion, it works properly.

.gitlab-ci.yml:

.dockerbuildpush: &dockerbuildpush
  - apk -q add py3-pip
  - pip install awscli --upgrade --user
  - /root/.local/bin/aws ecr get-login-password --region $AWS_REGION | docker login --username AWS --password-stdin $SHARED_AWS_ACCOUNT_ID.dkr.ecr.$AWS_REGION.amazonaws.com
  - docker build . -t $REPOSITORY_NAME:$CI_COMMIT_SHA
  - docker tag $REPOSITORY_NAME:$CI_COMMIT_SHA $SHARED_AWS_ACCOUNT_ID.dkr.ecr.$AWS_REGION.amazonaws.com/$REPOSITORY_NAME:$CONTAINER_VERSION 
  - docker push $SHARED_AWS_ACCOUNT_ID.dkr.ecr.$AWS_REGION.amazonaws.com/$REPOSITORY_NAME:$CONTAINER_VERSION

buildpushdev:
  image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/docker:19.03.12
  stage: buildpush
  tags:
    - pdpdevinternal
  rules:
    - if: '$CI_COMMIT_BRANCH == "develop"'
  services:
    - name: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/docker:19.03.12-dind
  variables:
    DOCKER_DRIVER: overlay2
    DOCKER_TLS_CERTDIR: ""
    CONTAINER_VERSION: develop
    AWS_REGION: us-east-1
    SHARED_AWS_ACCOUNT_ID: redacted
    REPOSITORY_NAME: redacted
  script:
    - *dockerbuildpush

Troubleshooting tried: Originally, I experienced this same problem using “docker:stable-dind”, but the gitlab support docs recommended that I specify the version, as seen above. I’ve followed the various fix recommendations in Docker:dind stops working after 12.1.0 update - #3 by timspin, including adding (to services):

- name: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/docker:19.03.12-dind
    #  entrypoint: ["env", "-u", "DOCKER_HOST"]
    #  command: ["dockerd-entrypoint.sh"]
    #- docker:stable-dind

and (to variables):
    #DOCKER_HOST: tcp://docker:2375/

But that didn’t change anything, either.

2

Found the problem, needed to add an alias to the services block:

  services:
    - name: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/docker:19.03.12-dind
      alias: docker