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Authenticate with registry in Docker-in-Docker

When you use Docker-in-Docker, the standard authentication methods do not work, because a fresh Docker daemon is started with the service.

Option 1: Run docker login

In before_script, run docker login:

default:
  image: docker:20.10.16
  services:
    - docker:20.10.16-dind

variables:
  DOCKER_TLS_CERTDIR: "/certs"

build:
  stage: build
  before_script:
    - echo "$DOCKER_REGISTRY_PASS" | docker login $DOCKER_REGISTRY --username $DOCKER_REGISTRY_USER --password-stdin
  script:
    - docker build -t my-docker-image .
    - docker run my-docker-image /script/to/run/tests

To sign in to Docker Hub, leave $DOCKER_REGISTRY empty or remove it.

Option 2: Mount ~/.docker/config.json on each job

If you are an administrator for GitLab Runner, you can mount a file with the authentication configuration to ~/.docker/config.json. Then every job that the runner picks up is already authenticated. If you are using the official docker:20.10.16 image, the home directory is under /root.

If you mount the configuration file, any docker command that modifies the ~/.docker/config.json fails. For example, docker login fails, because the file is mounted as read-only. Do not change it from read-only, because this causes problems.

Here is an example of /opt/.docker/config.json that follows the DOCKER_AUTH_CONFIG documentation:

{
    "auths": {
        "https://index.docker.io/v1/": {
            "auth": "bXlfdXNlcm5hbWU6bXlfcGFzc3dvcmQ="
        }
    }
}

Docker

Update the volume mounts to include the file.

[[runners]]
  ...
  executor = "docker"
  [runners.docker]
    ...
    privileged = true
    volumes = ["/opt/.docker/config.json:/root/.docker/config.json:ro"]

Kubernetes

Create a ConfigMap with the content of this file. You can do this with a command like:

kubectl create configmap docker-client-config --namespace gitlab-runner --from-file /opt/.docker/config.json

Update the volume mounts to include the file.

[[runners]]
  ...
  executor = "kubernetes"
  [runners.kubernetes]
    image = "alpine:3.12"
    privileged = true
    [[runners.kubernetes.volumes.config_map]]
      name = "docker-client-config"
      mount_path = "/root/.docker/config.json"
      # If you are running GitLab Runner 13.5
      # or lower you can remove this
      sub_path = "config.json"

Option 3: Use DOCKER_AUTH_CONFIG

If you already have DOCKER_AUTH_CONFIG defined, you can use the variable and save it in ~/.docker/config.json.

You can define this authentication in several ways:

The following example shows before_script. The same commands apply for any solution you implement.

default:
  image: docker:20.10.16
  services:
    - docker:20.10.16-dind

variables:
  DOCKER_TLS_CERTDIR: "/certs"

build:
  stage: build
  before_script:
    - mkdir -p $HOME/.docker
    - echo $DOCKER_AUTH_CONFIG > $HOME/.docker/config.json
  script:
    - docker build -t my-docker-image .
    - docker run my-docker-image /script/to/run/tests