For more information how to install Docker Engine on different systems checkout the [Supported installations](https://docs.docker.com/engine/installation/).
* By adding `gitlab-runner` to the `docker` group you are effectively granting `gitlab-runner` full root permissions.
For more information please read [On Docker security: `docker` group considered harmful](https://www.andreas-jung.com/contents/on-docker-security-docker-group-considered-harmful).
Docker-in-Docker works well, and is the recommended configuration, but it is not without its own challenges:
* By enabling `--docker-privileged`, you are effectively disabling all of
the security mechanisms of containers and exposing your host to privilege
escalation which can lead to container breakout. For more information, check out the official Docker documentation on
[Runtime privilege and Linux capabilities][docker-cap].
* Using docker-in-docker, each build is in a clean environment without the past
history. Concurrent builds work fine because every build gets it's own instance of docker engine so they won't conflict with each other. But this also means builds can be slower because there's no caching of layers.
* By default, `docker:dind` uses `--storage-driver vfs` which is the slowest form
The above command will register a new Runner to use the special
`docker:latest` image which is provided by Docker. **Notice that it's using
the Docker daemon of the Runner itself, and any containers spawned by docker commands will be siblings of the Runner rather than children of the runner.** This may have complications and limitations that are unsuitable for your workflow.
The above command will create a `config.toml` entry similar to this:
```
[[runners]]
url = "https://gitlab.com/ci"
token = REGISTRATION_TOKEN
executor = "docker"
[runners.docker]
tls_verify = false
image = "docker:latest"
privileged = false
disable_cache = false
volumes = ["/var/run/docker.sock", "/cache"]
[runners.cache]
Insecure = false
```
1. You can now use `docker` in the build script (note that you don't need to include the `docker:dind` service as when using the Docker in Docker executor):
```yaml
image: docker:latest
before_script:
- docker info
build:
stage: build
script:
- docker build -t my-docker-image .
- docker run my-docker-image /script/to/run/tests
```
While the above method avoids using Docker in privileged mode, you should be aware of the following implications:
* By sharing the docker daemon, you are effectively disabling all
the security mechanisms of containers and exposing your host to privilege
escalation which can lead to container breakout. For example, if a project
ran `docker rm -f $(docker ps -a -q)` it would remove the GitLab Runner
containers.
* Concurrent builds may not work; if your tests
create containers with specific names, they may conflict with each other.
* Sharing files and directories from the source repo into containers may not
work as expected since volume mounting is done in the context of the host
machine, not the build container.
e.g. `docker run --rm -t -i -v $(pwd)/src:/home/app/src test-image:latest run_app_tests`
## Using the GitLab Container Registry
> **Note:**
This feature requires GitLab 8.8 and GitLab Runner 1.2.
Once you've built a Docker image, you can push it up to the built-in [GitLab Container Registry](../../container_registry/README.md). For example, if you're using
docker-in-docker on your runners, this is how your `.gitlab-ci.yml` could look:
- docker run $CONTAINER_TEST_IMAGE /script/to/run/tests
test2:
stage: test
script:
- docker pull $CONTAINER_TEST_IMAGE
- docker run $CONTAINER_TEST_IMAGE /script/to/run/another/test
release-image:
stage: release
script:
- docker pull $CONTAINER_TEST_IMAGE
- docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
- docker push $CONTAINER_RELEASE_IMAGE
only:
- master
deploy:
stage: deploy
script:
- ./deploy.sh
only:
- master
```
Some things you should be aware of when using the Container Registry:
* You must log in to the container registry before running commands. Putting this in `before_script` will run it before each build job.
* Using `docker build --pull` makes sure that Docker fetches any changes to base images before building just in case your cache is stale. It takes slightly longer, but means you don’t get stuck without security patches to base images.
* Doing an explicit `docker pull` before each `docker run` makes sure to fetch the latest image that was just built. This is especially important if you are using multiple runners that cache images locally. Using the git SHA in your image tag makes this less necessary since each build will be unique and you shouldn't ever have a stale image, but it's still possible if you re-build a given commit after a dependency has changed.
* You don't want to build directly to `latest` in case there are multiple builds happening simultaneously.
