Run your CI/CD jobs in Docker containers

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You can run your CI/CD jobs in separate, isolated Docker containers.

If you run Docker on your local machine, you can run tests in the container, rather than testing on a dedicated CI/CD server.

To run CI/CD jobs in a Docker container, you need to:

Register a runner so that all jobs run in Docker containers. Do this by choosing the Docker executor during registration.
Specify which container to run the jobs in. Do this by specifying an image in your .gitlab-ci.yml file.
Optional. Run other services, like MySQL, in containers. Do this by specifying services in your .gitlab-ci.yml file.

Register a runner that uses the Docker executor

To use GitLab Runner with Docker you need to register a runner that uses the Docker executor.

This example shows how to set up a temporary template to supply services:

cat > /tmp/test-config.template.toml << EOF
[[runners]]
[runners.docker]
[[runners.docker.services]]
name = "postgres:latest"
[[runners.docker.services]]
name = "mysql:latest"
EOF

Then use this template to register the runner:

sudo gitlab-runner register \
  --url "https://gitlab.example.com/" \
  --registration-token "PROJECT_REGISTRATION_TOKEN" \
  --description "docker-ruby:2.6" \
  --executor "docker" \
  --template-config /tmp/test-config.template.toml \
  --docker-image ruby:2.6

The registered runner uses the ruby:2.6 Docker image and runs two services, postgres:latest and mysql:latest, both of which are accessible during the build process.

What is an image

The image keyword is the name of the Docker image the Docker executor uses to run CI/CD jobs.

By default, the executor pulls images from Docker Hub. However, you can configure the registry location in the gitlab-runner/config.toml file. For example, you can set the Docker pull policy to use local images.

For more information about images and Docker Hub, see the Docker overview.

Image requirements

Any image used to run a CI/CD job must have the following applications installed:

sh or bash
grep

Define `image` in the `.gitlab-ci.yml` file

You can define an image that's used for all jobs, and a list of services that you want to use during runtime:

default:
  image: ruby:2.6
  services:
    - postgres:11.7
  before_script:
    - bundle install

test:
  script:
    - bundle exec rake spec

The image name must be in one of the following formats:

image: <image-name> (Same as using <image-name> with the latest tag)
image: <image-name>:<tag>
image: <image-name>@<digest>

Extended Docker configuration options

Introduced in GitLab and GitLab Runner 9.4.

You can use a string or a map for the image or services entries:

Strings must include the full image name (including the registry, if you want to download the image from a registry other than Docker Hub).
Maps must contain at least the name option, which is the same image name as used for the string setting.

For example, the following two definitions are equal:

A string for image and services:

image: "registry.example.com/my/image:latest"

services:
  - postgresql:14.3
  - redis:latest

A map for image and services. The image:name is required:

image:
  name: "registry.example.com/my/image:latest"

services:
  - name: postgresql:14.3
  - name: redis:latest

Where scripts are executed

When a CI job runs in a Docker container, the before_script, script, and after_script commands run in the /builds/<project-path>/ directory. Your image may have a different default WORKDIR defined. To move to your WORKDIR, save the WORKDIR as an environment variable so you can reference it in the container during the job's runtime.

Override the entrypoint of an image

Introduced in GitLab and GitLab Runner 9.4. Read more about the extended configuration options.

Before explaining the available entrypoint override methods, let's describe how the runner starts. It uses a Docker image for the containers used in the CI/CD jobs:

The runner starts a Docker container using the defined entrypoint. The default from Dockerfile that may be overridden in the .gitlab-ci.yml file.
The runner attaches itself to a running container.
The runner prepares a script (the combination of before_script, script, and after_script).
The runner sends the script to the container's shell stdin and receives the output.

To override the entrypoint of a Docker image, define an empty entrypoint in the .gitlab-ci.yml file, so the runner does not start a useless shell layer. However, that does not work for all Docker versions.

For Docker 17.06 and later, the entrypoint can be set to an empty value.
For Docker 17.03 and earlier, the entrypoint can be set to /bin/sh -c, /bin/bash -c, or an equivalent shell available in the image.

The syntax of image:entrypoint is similar to Dockerfile ENTRYPOINT.

Let's assume you have a super/sql:experimental image with a SQL database in it. You want to use it as a base image for your job because you want to execute some tests with this database binary. Let's also assume that this image is configured with /usr/bin/super-sql run as an entrypoint. When the container starts without additional options, it runs the database's process. The runner expects that the image has no entrypoint or that the entrypoint is prepared to start a shell command.

With the extended Docker configuration options, instead of:

Creating your own image based on super/sql:experimental.
Setting the ENTRYPOINT to a shell.
Using the new image in your CI job.

You can now define an entrypoint in the .gitlab-ci.yml file.

For Docker 17.06 and later:

image:
  name: super/sql:experimental
  entrypoint: [""]

For Docker 17.03 and earlier:

image:
  name: super/sql:experimental
  entrypoint: ["/bin/sh", "-c"]

Define image and services in `config.toml`

Look for the [runners.docker] section:

[runners.docker]
  image = "ruby:latest"
  services = ["mysql:latest", "postgres:latest"]

The image and services defined this way are added to all jobs run by that runner.

Access an image from a private container registry

To access private container registries, the GitLab Runner process can use:

Statically defined credentials. That is, a username and password for a specific registry.
Credentials Store. For more information, see the relevant Docker documentation.
Credential Helpers. For more information, see the relevant Docker documentation.

To define which option should be used, the runner process reads the configuration in this order:

A DOCKER_AUTH_CONFIG CI/CD variable.
A DOCKER_AUTH_CONFIG environment variable set in the runner's config.toml file.
A config.json file in $HOME/.docker directory of the user running the process. If the --user flag is provided to run the child processes as unprivileged user, the home directory of the main runner process user is used.

Requirements and limitations

Available for Kubernetes executor in GitLab Runner 13.1 and later.
Credentials Store and Credential Helpers require binaries to be added to the GitLab Runner $PATH, and require access to do so. Therefore, these features are not available on instance runners, or any other runner where the user does not have access to the environment where the runner is installed.

Use statically-defined credentials

There are two approaches that you can take to access a private registry. Both require setting the CI/CD variable DOCKER_AUTH_CONFIG with appropriate authentication information.

Per-job: To configure one job to access a private registry, add DOCKER_AUTH_CONFIG as a CI/CD variable.
Per-runner: To configure a runner so all its jobs can access a private registry, add DOCKER_AUTH_CONFIG as an environment variable in the runner's configuration.

See below for examples of each.

Determine your `DOCKER_AUTH_CONFIG` data

As an example, let's assume you want to use the registry.example.com:5000/private/image:latest image. This image is private and requires you to sign in to a private container registry.

Let's also assume that these are the sign-in credentials:

Key	Value
registry	`registry.example.com:5000`
username	`my_username`
password	`my_password`

Use one of the following methods to determine the value for DOCKER_AUTH_CONFIG:

Do a docker login on your local machine:
```
docker login registry.example.com:5000 --username my_username --password my_password
```
Then copy the content of ~/.docker/config.json.

If you don't need access to the registry from your computer, you can do a docker logout:
```
docker logout registry.example.com:5000
```
In some setups, it's possible the Docker client uses the available system key store to store the result of docker login. In that case, it's impossible to read ~/.docker/config.json, so you must prepare the required base64-encoded version of ${username}:${password} and create the Docker configuration JSON manually. Open a terminal and execute the following command:
```
# The use of printf (as opposed to echo) prevents encoding a newline in the password.
printf "my_username:my_password" | openssl base64 -A

# Example output to copy
bXlfdXNlcm5hbWU6bXlfcGFzc3dvcmQ=
```
Create the Docker JSON configuration content as follows:
```
{
    "auths": {
        "registry.example.com:5000": {
            "auth": "(Base64 content from above)"
        }
    }
}
```

Configure a job

To configure a single job with access for registry.example.com:5000, follow these steps:

Create a CI/CD variable DOCKER_AUTH_CONFIG with the content of the Docker configuration file as the value:

{
    "auths": {
        "registry.example.com:5000": {
            "auth": "bXlfdXNlcm5hbWU6bXlfcGFzc3dvcmQ="
        }
    }
}

You can now use any private image from registry.example.com:5000 defined in image or services in your .gitlab-ci.yml file:
```
image: registry.example.com:5000/namespace/image:tag
```
In the example above, GitLab Runner looks at registry.example.com:5000 for the image namespace/image:tag.

You can add configuration for as many registries as you want, adding more registries to the "auths" hash as described above.

The full hostname:port combination is required everywhere for the runner to match the DOCKER_AUTH_CONFIG. For example, if registry.example.com:5000/namespace/image:tag is specified in the .gitlab-ci.yml file, then the DOCKER_AUTH_CONFIG must also specify registry.example.com:5000. Specifying only registry.example.com does not work.

Configuring a runner

If you have many pipelines that access the same registry, you should set up registry access at the runner level. This allows pipeline authors to have access to a private registry just by running a job on the appropriate runner. It also helps simplify registry changes and credential rotations.

This means that any job on that runner can access the registry with the same privilege, even across projects. If you need to control access to the registry, you need to be sure to control access to the runner.

To add DOCKER_AUTH_CONFIG to a runner:

Modify the runner's config.toml file as follows:
```
[[runners]]
  environment = ["DOCKER_AUTH_CONFIG={\"auths\":{\"registry.example.com:5000\":{\"auth\":\"bXlfdXNlcm5hbWU6bXlfcGFzc3dvcmQ=\"}}}"]
```
- The double quotes included in the DOCKER_AUTH_CONFIG data must be escaped with backslashes. This prevents them from being interpreted as TOML.
- The environment option is a list. Your runner may have existing entries and you should add this to the list, not replace it.
Restart the runner service.

Use a Credentials Store

To configure a Credentials Store:

To use a Credentials Store, you need an external helper program to interact with a specific keychain or external store. Make sure the helper program is available in the GitLab Runner $PATH.
Make GitLab Runner use it. There are two ways to accomplish this. Either:
- Create a CI/CD variable DOCKER_AUTH_CONFIG with the content of the Docker configuration file as the value:
```
  {
    "credsStore": "osxkeychain"
  }
```
- Or, if you're running self-managed runners, add the above JSON to ${GITLAB_RUNNER_HOME}/.docker/config.json. GitLab Runner reads this configuration file and uses the needed helper for this specific repository.

credsStore is used to access all the registries. If you use both images from a private registry and public images from Docker Hub, pulling from Docker Hub fails. Docker daemon tries to use the same credentials for all the registries.

Use Credential Helpers

Introduced in GitLab Runner 12.0.

As an example, let's assume that you want to use the <aws_account_id>.dkr.ecr.<region>.amazonaws.com/private/image:latest image. This image is private and requires you to sign in to a private container registry.

To configure access for <aws_account_id>.dkr.ecr.<region>.amazonaws.com, follow these steps:

Make sure docker-credential-ecr-login is available in the GitLab Runner $PATH.
Have any of the following AWS credentials setup. Make sure that GitLab Runner can access the credentials.
Make GitLab Runner use it. There are two ways to accomplish this. Either:
- Create a CI/CD variable DOCKER_AUTH_CONFIG with the content of the Docker configuration file as the value:
```
{
  "credHelpers": {
    "<aws_account_id>.dkr.ecr.<region>.amazonaws.com": "ecr-login"
  }
}
```
  This configures Docker to use the Credential Helper for a specific registry.
  
  Instead, you can configure Docker to use the Credential Helper for all Amazon Elastic Container Registry (ECR) registries:
```
{
  "credsStore": "ecr-login"
}
```
- Or, if you're running self-managed runners, add the previous JSON to ${GITLAB_RUNNER_HOME}/.docker/config.json. GitLab Runner reads this configuration file and uses the needed helper for this specific repository.
You can now use any private image from <aws_account_id>.dkr.ecr.<region>.amazonaws.com defined in image and/or services in your .gitlab-ci.yml file:
```
image: <aws_account_id>.dkr.ecr.<region>.amazonaws.com/private/image:latest
```
In the example, GitLab Runner looks at <aws_account_id>.dkr.ecr.<region>.amazonaws.com for the image private/image:latest.

You can add configuration for as many registries as you want, adding more registries to the "credHelpers" hash.

Use checksum to keep your image secure

We recommend using the image checksum in your job definition in your .gitlab-ci.yml file to verify the integrity of the image. A failed image integrity verification prevents you from using a modified container.

To use the image checksum you have to append the checksum at the end:

image: ruby:2.6.8@sha256:d1dbaf9665fe8b2175198e49438092fdbcf4d8934200942b94425301b17853c7

To get the image checksum, on the image TAG tab, view the DIGEST column. For example, view the Ruby image. The checksum is a random string, like 6155f0235e95.

You can also get the checksum of any image on your system with the command docker images --digests:

❯ docker images --digests
REPOSITORY                                                        TAG       DIGEST                                                                    (...)
gitlab/gitlab-ee                                                  latest    sha256:723aa6edd8f122d50cae490b1743a616d54d4a910db892314d68470cc39dfb24   (...)
gitlab/gitlab-runner                                              latest    sha256:4a18a80f5be5df44cb7575f6b89d1fdda343297c6fd666c015c0e778b276e726   (...)

Creating a Custom GitLab Runner Docker Image

You can create a custom GitLab Runner Docker image to package AWS CLI and Amazon ECR Credential Helper. This setup facilitates secure and streamlined interactions with AWS services, especially for containerized applications. For example, to reduce time and error-prone manual configurations, teams who deploy microservices on AWS can use this setup to manage, deploy, and update Docker images on Amazon ECR, without using manual credential management.

Authenticate GitLab with AWS.

Create a Dockerfile with the following content:

  # Control package versions
  ARG GITLAB_RUNNER_VERSION=v16.4.0
  ARG AWS_CLI_VERSION=2.2.30

  # AWS CLI and Amazon ECR Credential Helper
  FROM amazonlinux as aws-tools
  RUN set -e \
      && yum update -y \
      && yum install -y --allowerasing git make gcc curl unzip \
      && curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" --output "awscliv2.zip" \
      && unzip awscliv2.zip && ./aws/install -i /usr/local/bin \
      && yum clean all

  # Download and install ECR Credential Helper
  RUN curl --location --output  /usr/local/bin/docker-credential-ecr-login "https://github.com/awslabs/amazon-ecr-credential-helper/releases/latest/download/docker-credential-ecr-login-linux-amd64"
  RUN chmod +x /usr/local/bin/docker-credential-ecr-login

  # Configure the ECR Credential Helper
  RUN mkdir -p /root/.docker
  RUN echo '{ "credsStore": "ecr-login" }' > /root/.docker/config.json

  # Final image based on GitLab Runner
  FROM gitlab/gitlab-runner:${GITLAB_RUNNER_VERSION}

  # Install necessary packages
  RUN apt-get update \
      && apt-get install -y --no-install-recommends jq procps curl unzip groff libgcrypt20 tar gzip less openssh-client \
      && apt-get clean && rm -rf /var/lib/apt/lists/*

  # Copy AWS CLI and Amazon ECR Credential Helper binaries
  COPY --from=aws-tools /usr/local/bin/ /usr/local/bin/

  # Copy ECR Credential Helper Configuration
  COPY --from=aws-tools /root/.docker/config.json /root/.docker/config.json

To build the custom GitLab Runner Docker image within a .gitlab-ci.yml, include the following example below:

variables:
  DOCKER_DRIVER: overlay2
  IMAGE_NAME: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
  GITLAB_RUNNER_VERSION: v16.4.0
  AWS_CLI_VERSION: 2.13.21

stages:
  - build

build-image:
  stage: build
  script:
    - echo "Logging into GitLab container registry..."
    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
    - echo "Building Docker image..."
    - docker build --build-arg GITLAB_RUNNER_VERSION=${GITLAB_RUNNER_VERSION} --build-arg AWS_CLI_VERSION=${AWS_CLI_VERSION} -t ${IMAGE_NAME} .
    - echo "Pushing Docker image to GitLab container registry..."
    - docker push ${IMAGE_NAME}
  rules:
    - changes:
        - Dockerfile

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