Docker executor

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GitLab Runner uses the Docker executor to run jobs on Docker images.

You can use the Docker executor to:

  • Maintain the same build environment for each job.
  • Use the same image to test commands locally without the requirement of running a job in the CI server.

The Docker executor uses Docker Engine to run each job in a separate and isolated container. To connect to Docker Engine, the executor uses:

Docker executor workflow

The Docker executor uses a special Docker image based on Alpine Linux that contains the tools to run the prepare, pre-job, and post-job steps. To view the definition of the special Docker image, see the GitLab Runner repository.

The Docker executor divides the job into several steps:

  1. Prepare: Creates and starts the services.
  2. Pre-job: Clones, restores cache, and downloads artifacts from previous stages. Runs on a special Docker image.
  3. Job: Runs your build in the Docker image you configure for the runner.
  4. Post-job: Create cache, upload artifacts to GitLab. Runs on a special Docker Image.

Supported configurations

The Docker executor supports the following configurations.

For known issues and additional requirements of Windows configurations, see Use Windows containers.

Runner is installed on: Executor is: Container is running:
Windows docker-windows Windows
Windows docker Linux
Linux docker Linux

These configurations are not supported:

Runner is installed on: Executor is: Container is running:
Linux docker-windows Linux
Linux docker Windows
Linux docker-windows Windows
Windows docker Windows
Windows docker-windows Linux
note
GitLab Runner uses Docker Engine API v1.25 to talk to the Docker Engine. This means the minimum supported version of Docker on a Linux server is 1.13.0, on Windows Server it needs to be more recent to identify the Windows Server version.

Use the Docker executor

To use the Docker executor, define Docker as the executor in config.toml.

The following sample shows Docker defined as the executor and example configurations. For more information about these values, see Advanced configuration 

concurrent = 4

[[runners]]
name = "myRunner"
url = "https://gitlab.com/ci"
token = "......"
executor = "docker"
[runners.docker]
  tls_verify = true
  image = "my.registry.tld:5000/alpine:latest"
  privileged = false
  disable_entrypoint_overwrite = false
  oom_kill_disable = false
  disable_cache = false
  volumes = [
    "/cache",
  ]
  shm_size = 0
  allowed_pull_policies = ["always", "if-not-present"]
  allowed_images = ["my.registry.tld:5000/*:*"]
  allowed_services = ["my.registry.tld:5000/*:*"]
  [runners.docker.volume_driver_ops]
    "size" = "50G"

Configure images and services

Prerequisites:

  • The image where your job runs must have a working shell in its operating system PATH. Supported shells are:

To configure the Docker executor, you define the Docker images and services in .gitlab-ci.yml and config.toml.

Use the following keywords:

  • image: The name of the Docker image that the runner uses to run jobs.
    • Enter an image from the local Docker Engine, or any image in Docker Hub. For more information, see the Docker documentation.
    • To define the image version, use a colon (:) to add a tag. If you don’t specify a tag, Docker uses latest as the version.
  • services: The additional image that creates another container and links to the image. For more information about types of services, see Services.

Define images and services in .gitlab-ci.yml

Define an image that the runner uses for all jobs and a list of services to use during build time.

Example: 

image: ruby:2.7

services:
  - postgres:9.3

before_script:
  - bundle install

test:
  script:
  - bundle exec rake spec

To define different images and services per job: 

before_script:
  - bundle install

test:2.6:
  image: ruby:2.6
  services:
  - postgres:9.3
  script:
  - bundle exec rake spec

test:2.7:
  image: ruby:2.7
  services:
  - postgres:9.4
  script:
  - bundle exec rake spec

If you don’t define an image in .gitlab-ci.yml, the runner uses the image defined in config.toml.

Define images and services in config.toml

To add images and services to all jobs run by a runner, update [runners.docker] in the config.toml. If you don’t define an image in .gitlab-ci.yml, the runner uses the image defined in config.toml.

Example: 

[runners.docker]
  image = "ruby:2.7"

[[runners.docker.services]]
  name = "mysql:latest"
  alias = "db"

[[runners.docker.services]]
  name = "redis:latest"
  alias = "cache"

This example uses the array of tables syntax.

Define an image from a private registry

Prerequisites:

To define an image from a private registry, provide the registry name and the image in .gitlab-ci.yml.

Example: 

image: my.registry.tld:5000/namespace/image:tag

In this example, GitLab Runner searches the registry my.registry.tld:5000 for the image namespace/image:tag.

Network configurations

You must configure a network to connect services to a CI/CD job.

To configure a network, you can either:

  • Recommended. Configure the runner to create a network for each job.
  • Define container links. Container links are a legacy feature of Docker.

Create a network for each job

You can configure the runner to create a network for each job.

When you enable this networking mode, the runner creates and uses a user-defined Docker bridge network for each job. Docker environment variables are not shared across the containers. For more information about user-defined bridge networks, see the Docker documentation.

To use this networking mode, enable FF_NETWORK_PER_BUILD in either the feature flag or the environment variable in the config.toml.

Do not set the network_mode.

Example: 

[[runners]]
  (...)
  executor = "docker"
  environment = ["FF_NETWORK_PER_BUILD=1"]

Or: 

[[runners]]
  (...)
  executor = "docker"
  [runners.feature_flags]
    FF_NETWORK_PER_BUILD = true

To set the default Docker address pool, use default-address-pool in dockerd. If CIDR ranges are already used in the network, Docker networks may conflict with other networks on the host, including other Docker networks.

This feature works only when the Docker daemon is configured with IPv6 enabled. To enable IPv6 support, set enable_ipv6 to true in the Docker configuration. For more information, see the Docker documentation.

The runner uses the build alias to resolve the job container.

How the runner creates a network for each job

When a job starts, the runner:

  1. Creates a bridge network, similar to the Docker command docker network create <network>.
  2. Connects the service and containers to the bridge network.
  3. Removes the network at the end of the job.

The container running the job and the containers running the service resolve each other’s hostnames and aliases. This functionality is provided by Docker.

You can configure a network mode that uses Docker legacy container links and the default Docker bridge to link the job container with the services. This network mode is the default if FF_NETWORK_PER_BUILD is not enabled.

To configure the network, specify the networking mode in the config.toml file:

  • bridge: Use the bridge network. Default.
  • host: Use the host’s network stack inside the container.
  • none: No networking. Not recommended.

Example: 

[[runners]]
  (...)
  executor = "docker"
[runners.docker]
  network_mode = "bridge"

If you use any other network_mode value, these are taken as the name of an already existing Docker network, which the build container connects to.

During name resolution, Docker updates the /etc/hosts file in the container with the service container hostname and alias. However, the service container is not able to resolve the container name. To resolve the container name, you must create a network for each job.

Linked containers share their environment variables.

Overriding the MTU of the created network

For some environments, like virtual machines in OpenStack, a custom MTU is necessary. The Docker daemon does not respect the MTU in docker.json (see Moby issue 34981). You can set network_mtu in your config.toml to any valid value so the Docker daemon can use the correct MTU for the newly created network. You must also enable FF_NETWORK_PER_BUILD for the override to take effect.

The following configuration sets the MTU to 1402 for the network created for each job. Make sure to adjust the value to your specific environment requirements. 

[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    network_mtu = 1402
    [runners.feature_flags]
      FF_NETWORK_PER_BUILD = true

Restrict Docker images and services

To restrict Docker images and services, specify a wildcard pattern in the allowed_images and allowed_services parameters.

For example, to allow images from your private Docker registry only: 

[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    (...)
    allowed_images = ["my.registry.tld:5000/*:*"]
    allowed_services = ["my.registry.tld:5000/*:*"]

To restrict to a list of images from your private Docker registry: 

[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    (...)
    allowed_images = ["my.registry.tld:5000/ruby:*", "my.registry.tld:5000/node:*"]
    allowed_services = ["postgres:9.4", "postgres:latest"]

Access services hostnames

To access a service hostname, add the service to services in .gitlab-ci.yml.

For example, to use a Wordpress instance to test an API integration with your application, use tutum/wordpress as the service image: 

services:
- tutum/wordpress:latest

When the job runs, the tutum/wordpress service starts. You can access it from your build container under the hostname tutum__wordpress and tutum-wordpress.

In addition to the specified service aliases, the runner assigns the name of the service image as an alias to the service container. You can use any of these aliases.

The runner uses the following rules to create the alias based on the image name:

  • Everything after : is stripped.
  • For the first alias, the slash (/) is replaced with double underscores (__).
  • For the second alias, the slash (/) is replaced with a single dash (-).

If you use a private service image, the runner strips any specified port and applies the rules. The service registry.gitlab-wp.com:4999/tutum/wordpress results in the hostname registry.gitlab-wp.com__tutum__wordpress and registry.gitlab-wp.com-tutum-wordpress.

Configuring services

To change database names or set account names, you can define environment variables for the service.

When the runner passes variables:

  • Variables are passed to all containers. The runner cannot pass variables to specific containers.
  • Secure variables are passed to the build container.

For more information about configuration variables, see the documentation of each image provided in their corresponding Docker Hub page.

Mount a directory in RAM

You can use the tmpfs option to mount a directory in RAM. This speeds up the time required to test if there is a lot of I/O related work, such as with databases.

If you use the tmpfs and services_tmpfs options in the runner configuration, you can specify multiple paths, each with its own options. For more information, see the Docker documentation.

For example, to mount the data directory for the official MySQL container in RAM, configure the config.toml: 

[runners.docker]
  # For the main container
  [runners.docker.tmpfs]
      "/var/lib/mysql" = "rw,noexec"

  # For services
  [runners.docker.services_tmpfs]
      "/var/lib/mysql" = "rw,noexec"

Building a directory in a service

GitLab Runner mounts a /builds directory to all shared services.

For more information about using different services see:

How GitLab Runner performs the services health check

History

After the service starts, GitLab Runner waits for the service to respond. The Docker executor tries to open a TCP connection to the exposed service port in the service container.

  • In GitLab 15.11 and earlier, only the first exposed port is checked.
  • In GitLab 16.0 and later, the first 20 exposed ports are checked.

The HEALTHCHECK_TCP_PORT service variable can be used to perform the health check on a specific port: 

job:
  services:
    - name: mongo
      variables:
        HEALTHCHECK_TCP_PORT: "27017"

To see how this is implemented, use the health check Go command.

Specify Docker driver operations

Specify arguments to supply to the Docker volume driver when you create volumes for builds. For example, you can use these arguments to limit the space for each build to run, in addition to all other driver specific options. The following example shows a config.toml where the limit that each build can consume is set to 50GB. 

[runners.docker]
  [runners.docker.volume_driver_ops]
      "size" = "50G"

Configure directories for the container build and cache

To define where data is stored in the container, configure /builds and /cache directories in the [[runners]] section in config.toml.

If you modify the /cache storage path, to mark the path as persistent you must define it in volumes = ["/my/cache/"], under the [runners.docker] section in config.toml.

By default, the Docker executor stores builds and caches in the following directories:

  • Builds in /builds/<namespace>/<project-name>
  • Caches in /cache inside the container.

Clear the Docker cache

History

Use clear-docker-cache to remove unused containers and volumes created by the runner.

For a list of options, run the script with the help option: 

clear-docker-cache help

The default option is prune-volumes, which removes all unused containers (dangling and unreferenced) and volumes.

To manage cache storage efficiently, you should:

  • Run clear-docker-cache with cron regularly (for example, once a week).
  • Maintain some recent containers in the cache for performance while you reclaim disk space.

Clear Docker build images

The clear-docker-cache script does not remove Docker images because they are not tagged by the GitLab Runner.

To clear Docker build images:

  1. Confirm what disk space can be reclaimed: 

     clear-docker-cache space

 Show docker disk usage
 ----------------------

 TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
 Images          14        9         1.306GB   545.8MB (41%)
 Containers      19        18        115kB     0B (0%)
 Local Volumes   0         0         0B        0B
 Build Cache     0         0         0B        0B

  2. To remove all unused containers, networks, images (dangling and unreferenced), and untagged volumes, run docker system prune.

Persistent storage

The Docker executor provides persistent storage when it runs containers. All directories defined in volumes = are persistent between builds.

The volumes directive supports the following types of storage:

  • For dynamic storage, use <path>. The <path> is persistent between subsequent runs of the same concurrent job for that project. The data is attached to a custom cache volume: runner-<short-token>-project-<id>-concurrent-<concurrency-id>-cache-<md5-of-path>.
  • For host-bound storage, use <host-path>:<path>[:<mode>]. The <path> is bound to <host-path> on the host system. The optional <mode> specifies that this storage is read-only or read-write (default).

Persistent storage for builds

If you make the /builds directory a host-bound storage, your builds are stored in: /builds/<short-token>/<concurrent-id>/<namespace>/<project-name>, where:

  • <short-token> is a shortened version of the Runner’s token (first 8 letters).
  • <concurrent-id> is a unique number that identifies the local job ID of the particular runner in context of the project.

IPC mode

The Docker executor supports sharing the IPC namespace of containers with other locations. This maps to the docker run --ipc flag. More details on IPC settings in Docker documentation

Privileged mode

The Docker executor supports a number of options that allows fine-tuning of the build container. One of these options is the privileged mode.

Use Docker-in-Docker with privileged mode

The configured privileged flag is passed to the build container and all services, thus allowing to easily use the Docker-in-Docker approach.

First, configure your runner (config.toml) to run in privileged mode: 

[[runners]]
  executor = "docker"
  [runners.docker]
    privileged = true

Then, make your build script (.gitlab-ci.yml) to use Docker-in-Docker container: 

image: docker:git
services:
- docker:dind

build:
  script:
  - docker build -t my-image .
  - docker push my-image
caution
Containers that run in privileged mode have security risks. When your containers run in privileged mode, you disable the container security mechanisms and expose your host to privilege escalation. Running containers in privileged mode can lead to container breakout. For more information, see the Docker documentation about runtime privilege and Linux capabilities.

You might need to configure Docker in Docker with TLS, or disable TLS to avoid an error similar to the following: 

Cannot connect to the Docker daemon at tcp://docker:2375. Is the docker daemon running?

Use rootless Docker-in-Docker with restricted privileged mode

In this version, only Docker-in-Docker rootless images are allowed to run as services in privileged mode.

The services_privileged and allowed_privileged_services configuration parameters limit which containers are allowed to run in privileged mode.

To use rootless Docker-in-Docker with restricted privileged mode:

  1. In the config.toml, configure the runner to use services_privileged and allowed_privileged_services: 

    [[runners]]
  executor = "docker"
  [runners.docker]
    services_privileged = true
    allowed_privileged_services = ["docker.io/library/docker:*-dind-rootless", "docker.io/library/docker:dind-rootless", "docker:*-dind-rootless", "docker:dind-rootless"]

  2. In .gitlab-ci.yml, edit your build script to use Docker-in-Docker rootless container: 

    image: docker:git
services:
- docker:dind-rootless

build:
  script:
  - docker build -t my-image .
  - docker push my-image

Only the Docker-in-Docker rootless images you list in allowed_privileged_services are allowed to run in privileged mode. All other containers for jobs and services run in unprivileged mode.

Because they run as non-root, it’s almost safe to use with privileged mode images like Docker-in-Docker rootless or Buildkit rootless.

For more information about security issues, see Security risks for Docker executors.

Configure a Docker ENTRYPOINT

By default the Docker executor doesn’t override the ENTRYPOINT of a Docker image and passes sh or bash as COMMAND to start a container that runs the job script.

To ensure a job can run, its Docker image must:

  • Provide sh or bash and grep
  • Define an ENTRYPOINT that starts a shell when passed sh/bash as argument

The Docker Executor runs the job’s container with an equivalent of the following command: 

docker run <image> sh -c "echo 'It works!'" # or bash

If your Docker image doesn’t support this mechanism, you can override the image’s ENTRYPOINT in the project configuration as follows: 

# Equivalent of
# docker run --entrypoint "" <image> sh -c "echo 'It works!'"
image:
  name: my-image
  entrypoint: [""]

For more information, see Override the Entrypoint of an image and How CMD and ENTRYPOINT interact in Docker.

Job script as ENTRYPOINT

You can use ENTRYPOINT to create a Docker image that runs the build script in a custom environment, or in secure mode.

For example, you can create a Docker image that uses an ENTRYPOINT that doesn’t execute the build script. Instead, the Docker image executes a predefined set of commands to build the Docker image from your directory. You run the build container in privileged mode, and secure the build environment of the runner.

  1. Create a new Dockerfile: 

    FROM docker:dind
ADD / /entrypoint.sh
ENTRYPOINT ["/bin/sh", "/entrypoint.sh"]

  2. Create a bash script (entrypoint.sh) that is used as the ENTRYPOINT: 

    #!/bin/sh

dind docker daemon
    --host=unix:///var/run/docker.sock \
    --host=tcp://0.0.0.0:2375 \
    --storage-driver=vf &

docker build -t "$BUILD_IMAGE" .
docker push "$BUILD_IMAGE"

  3. Push the image to the Docker registry.

  4. Run Docker executor in privileged mode. In config.toml define: 

    [[runners]]
  executor = "docker"
  [runners.docker]
    privileged = true

  5. In your project use the following .gitlab-ci.yml: 

    variables:
  BUILD_IMAGE: my.image
build:
  image: my/docker-build:image
  script:
  - Dummy Script

Use Podman to run Docker commands

History

If you have GitLab Runner installed on Linux, your jobs can use Podman to replace Docker as the container runtime in the Docker executor.

Prerequisites:

  1. On your Linux host, install GitLab Runner. If you installed GitLab Runner by using your system’s package manager, it automatically creates a gitlab-runner user.
  2. Sign in as the user that will run GitLab Runner. You must do so in a way that doesn’t go around pam_systemd. You can use SSH with the correct user. This ensures you can run systemctl as this user.
  3. Make sure that your system fulfills the prerequisites for a rootless Podman setup. Specifically, make sure your user has correct entries in /etc/subuid and /etc/subgid.
  4. On the Linux host, install Podman.

  5. Enable and start the Podman socket: 

    systemctl --user --now enable podman.socket

  6. Verify the Podman socket is listening: 

    systemctl status --user podman.socket
  7. Copy the socket string in the Listen key through which Podman’s API is being accessed.

  8. Make sure the Podman socket remains available after the GitLab Runner user is logged out: 

    sudo loginctl enable-linger gitlab-runner

  9. Edit the GitLab Runner config.toml file and add the socket value to the host entry in the [runners.docker] section. For example: 

    [[runners]]
  name = "podman-test-runner-2022-06-07"
  url = "https://gitlab.com"
  token = "x-XxXXXXX-xxXxXxxxxx"
  executor = "docker"
  [runners.docker]
    host = "unix:///run/user/1012/podman/podman.sock"
    tls_verify = false
    image = "quay.io/podman/stable"
    privileged = true

Use Podman to build container images from a Dockerfile

The following example uses Podman to build a container image and push the image to the GitLab Container registry.

The default container image in the Runner config.toml is set to quay.io/podman/stable, so that the CI job uses that image to execute the included commands. 

variables:
  IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG

before_script:
  - podman login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY

oci-container-build:
  stage: build
  script:
    - podman build -t $IMAGE_TAG .
    - podman push $IMAGE_TAG
  when: manual

Use Buildah to build container images from a Dockerfile

The following example shows how to use Buildah to build a container image and push the image to the GitLab Container registry. 

image: quay.io/buildah/stable

variables:
  IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG

before_script:
  - buildah login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY

oci-container-build:
  stage: build
  script:
    - buildah bud -t $IMAGE_TAG .
    - buildah push $IMAGE_TAG
  when: manual

Specify which user runs the job

By default, the runner runs jobs as the root user within the container. To specify a different, non-root user to run the job, use the USER directive in the Dockerfile of the Docker image. 

FROM amazonlinux
RUN ["yum", "install", "-y", "nginx"]
RUN ["useradd", "www"]
USER "www"
CMD ["/bin/bash"]

When you use that Docker image to execute your job, it runs as the specified user: 

build:
  image: my/docker-build:image
  script:
  - whoami   # www

Configure how runners pull images

Configure the pull policy in the config.toml to define how runners pull Docker images from registries. You can set a single policy, a list of policies, or allow specific pull policies.

Use the following values for the pull_policy:

  • always: Pull an image even if a local image exists. Default.
  • if-not-present: Pull an image only when a local version does not exist.
  • never: Never pull an image and use only local images. 
[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    (...)
    pull_policy = "always" # available: always, if-not-present, never

Set the always pull policy

The always option, which is on by default, always initiates a pull before creating the container. This option makes sure the image is up-to-date, and prevents you from using outdated images even if a local image exists.

Use this pull policy if:

  • Runners must always pull the most recent images.
  • Runners are publicly available and configured for auto-scale or as a shared runner in your GitLab instance.

Do not use this policy if runners must use locally stored images.

Set always as the pull policy in the config.toml: 

[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    (...)
    pull_policy = "always"

Set the if-not-present pull policy

When you set the pull policy to if-not-present, the runner first checks if a local image exists. If there is no local image, the runner pulls an image from the registry.

Use the if-not-present policy to:

  • Use local images but also pull images if a local image does not exist.
  • Reduce time that runners analyze the difference in image layers for heavy and rarely updated images. In this case, you must manually remove the image regularly from the local Docker Engine store to force the image update.

Do not use this policy:

  • For shared runners where different users that use the runner may have access to private images. For more information about security issues, see Usage of private Docker images with if-not-present pull policy.
  • If jobs are frequently updated and must be run in the most recent image version. This may result in a network load reduction that outweighs the value of frequent deletion of local images.

Set the if-not-present policy in the config.toml: 

[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    (...)
    pull_policy = "if-not-present"

Set the never pull policy

Prerequisites:

  • Local images must contain an installed Docker Engine and a local copy of used images.

When you set the pull policy to never, image pulling is disabled. Users can only use images that have been manually pulled on the Docker host where the runner runs.

Use the never pull policy:

  • To control the images used by runner users.
  • For private runners that are dedicated to a project that can only use specific images that are not publicly available on any registries.

Do not use the never pull policy for auto-scaled Docker executors. The never pull policy is usable only when using a pre-defined cloud instance images for chosen cloud provider.

Set the never policy in the config.toml: 

[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    (...)
    pull_policy = "never"

Set multiple pull policies

History

You can list multiple pull policies to execute if a pull fails. The runner processes pull policies in the order listed until a pull attempt is successful or the list is exhausted. For example, if a runner uses the always pull policy and the registry is not available, you can add the if-not-present as a second pull policy to use a locally cached Docker image.

For information about the security implications of this pull policy, see Usage of private Docker images with if-not-present pull policy.

To set multiple pull policies, add them as a list in the config.toml: 

[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    (...)
    pull_policy = ["always", "if-not-present"]

Allow Docker pull policies

History

In the .gitlab-ci.yml file, you can specify a pull policy. This policy determines how a CI/CD job fetches images.

To restrict which pull policies can be used in the .gitlab-ci.yml file, use allowed_pull_policies.

For example, to allow only the always and if-not-present pull policies, add them to the config.toml: 

[[runners]]
  (...)
  executor = "docker"
  [runners.docker]
    (...)
    allowed_pull_policies = ["always", "if-not-present"]
  • If you don’t specify allowed_pull_policies, the default is the value in the pull_policy keyword.
  • If you don’t specify pull_policy, the default is always.
  • The existing pull_policy keyword must not include a pull policy that is not specified in allowed_pull_policies. If it does, the job returns an error.

Image pull error messages

Error message Description
Pulling docker image registry.tld/my/image:latest ... ERROR: Build failed: Error: image registry.tld/my/image:latest not found The runner cannot find the image. Displays when the always pull policy is set
Pulling docker image local_image:latest ... ERROR: Build failed: Error: image local_image:latest not found The image was built locally and doesn’t exist in any public or default Docker registry. Displays when the always pull policy is set.
Pulling docker image registry.tld/my/image:latest ... WARNING: Cannot pull the latest version of image registry.tld/my/image:latest : Error: image registry.tld/my/image:latest not found WARNING: Locally found image will be used instead. The runner has used a local image instead of pulling an image. Displays when the always pull policy is set in only GitLab Runner 1.8 and earlier.
Pulling docker image local_image:latest ... ERROR: Build failed: Error: image local_image:latest not found The image cannot be found locally. Displays when the never pull policy is set.
WARNING: Failed to pull image with policy "always": Error response from daemon: received unexpected HTTP status: 502 Bad Gateway (docker.go:143:0s) Attempt #2: Trying "if-not-present" pull policy Using locally found image version due to "if-not-present" pull policy The runner failed to pull an image and attempts to pull an image by using the next listed pull policy. Displays when multiple pull policies are set.

Retry a failed pull

To configure a runner to retry a failed image pull, specify the same policy more than once in the config.toml.

For example, this configuration retries the pull one time: 

[runners.docker]
  pull_policy = ["always", "always"]

This setting is similar to the retry directive in the .gitlab-ci.yml files of individual projects, but only takes effect if specifically the Docker pull fails initially.

Use Windows containers

History

To use Windows containers with the Docker executor, note the following information about limitations, supported Windows versions, and configuring a Windows Docker executor.

Nanoserver support

History

With the support for PowerShell Core introduced in the Windows helper image, it is now possible to leverage the nanoserver variants for the helper image.

Limitations of Docker executor on Windows

The following are some limitations of using Windows containers with Docker executor:

  • Docker-in-Docker is not supported, since it’s not supported by Docker itself.
  • Interactive web terminals are not supported.
  • Host device mounting not supported.
  • When mounting a volume directory it has to exist, or Docker will fail to start the container, see #3754 for additional detail.
  • docker-windows executor can be run only using GitLab Runner running on Windows.
  • Linux containers on Windows are not supported, since they are still experimental. Read the relevant issue for more details.

  • Because of a limitation in Docker, if the destination path drive letter is not c:, paths are not supported for:

    This means values such as f:\\cache_dir are not supported, but f: is supported. However, if the destination path is on the c: drive, paths are also supported (for example c:\\cache_dir).

    To configure where the Docker daemon keeps images and containers, update the data-root parameter in the daemon.json file of the Docker daemon.

    For more information, see Configure Docker with a configuration file.

Supported Windows versions

GitLab Runner only supports the following versions of Windows which follows our support lifecycle for Windows:

  • Windows Server 2022 LTSC (21H2)
  • Windows Server 2019 LTSC (1809)

For future Windows Server versions, we have a future version support policy.

You can only run containers based on the same OS version that the Docker daemon is running on. For example, the following Windows Server Core images can be used:

  • mcr.microsoft.com/windows/servercore:ltsc2022
  • mcr.microsoft.com/windows/servercore:ltsc2022-amd64
  • mcr.microsoft.com/windows/servercore:1809
  • mcr.microsoft.com/windows/servercore:1809-amd64
  • mcr.microsoft.com/windows/servercore:ltsc2019

Supported Docker versions

A Windows Server running GitLab Runner must be running a recent version of Docker because GitLab Runner uses Docker to detect what version of Windows Server is running.

A known version of Docker that doesn’t work with GitLab Runner is Docker 17.06 since Docker does not identify the version of Windows Server resulting in the following error: 

unsupported Windows Version: Windows Server Datacenter

Read more about troubleshooting this.

Configure a Windows Docker executor

note
When a runner is registered with c:\\cache as a source directory when passing the --docker-volumes or DOCKER_VOLUMES environment variable, there is a known issue.

Below is an example of the configuration for a simple Docker executor running Windows. 

[[runners]]
  name = "windows-docker-2019"
  url = "https://gitlab.com/"
  token = "xxxxxxx"
  executor = "docker-windows"
  [runners.docker]
    image = "mcr.microsoft.com/windows/servercore:1809_amd64"
    volumes = ["c:\\cache"]

For other configuration options for the Docker executor, see the advanced configuration section.

Services

In GitLab Runner 12.9 and later, you can use services by enabling a network for each job.