--- stage: Verify group: Runner info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers type: concepts, howto --- # Using Docker images GitLab CI/CD in conjunction with [GitLab Runner](../runners/README.md) can use [Docker Engine](https://www.docker.com/) to test and build any application. Docker is an open-source project that allows you to use predefined images to run applications in independent "containers" that are run within a single Linux instance. [Docker Hub](https://hub.docker.com/) has a rich database of pre-built images that can be used to test and build your applications. When used with GitLab CI/CD, Docker runs each job in a separate and isolated container using the predefined image that's set up in [`.gitlab-ci.yml`](../yaml/README.md). This makes it easier to have a simple and reproducible build environment that can also run on your workstation. The added benefit is that you can test all the commands that we explore later from your shell, rather than having to test them on a dedicated CI server. ## Register Docker Runner To use GitLab Runner with Docker you need to [register a new runner](https://docs.gitlab.com/runner/register/) to use the `docker` executor. An example can be seen below. First we set up a temporary template to supply the services: ```shell cat > /tmp/test-config.template.toml << EOF [[runners]] [runners.docker] [[runners.docker.services]] name = "postgres:latest" [[runners.docker.services]] name = "mysql:latest" EOF ``` Then we register the runner using the template that was just created: ```shell 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 runs to perform the CI tasks. By default, the executor only pulls images from [Docker Hub](https://hub.docker.com/), however this can be configured in the `gitlab-runner/config.toml` by setting the [Docker pull policy](https://docs.gitlab.com/runner/executors/docker.html#how-pull-policies-work) to allow using local images. For more information about images and Docker Hub, please read the [Docker Fundamentals](https://docs.docker.com/engine/understanding-docker/) documentation. ## What is a service The `services` keyword defines just another Docker image that's run during your job and is linked to the Docker image that the `image` keyword defines. This allows you to access the service image during build time. The service image can run any application, but the most common use case is to run a database container, for example, `mysql`. It's easier and faster to use an existing image and run it as an additional container than install `mysql` every time the project is built. You're not limited to have only database services. You can add as many services you need to `.gitlab-ci.yml` or manually modify `config.toml`. Any image found at [Docker Hub](https://hub.docker.com/) or your private Container Registry can be used as a service. Services inherit the same DNS servers, search domains, and additional hosts as the CI container itself. You can see some widely used services examples in the relevant documentation of [CI services examples](../services/README.md). ### How services are linked to the job To better understand how the container linking works, read [Linking containers together](https://docs.docker.com/engine/userguide/networking/default_network/dockerlinks/). To summarize, if you add `mysql` as service to your application, the image is then used to create a container that's linked to the job container. The service container for MySQL is accessible under the hostname `mysql`. So, in order to access your database service you have to connect to the host named `mysql` instead of a socket or `localhost`. Read more in [accessing the services](#accessing-the-services). ### How the health check of services works Services are designed to provide additional functionality which is **network accessible**. It may be a database like MySQL, or Redis, and even `docker:stable-dind` which allows you to use Docker in Docker. It can be practically anything that's required for the CI/CD job to proceed and is accessed by network. To make sure this works, the runner: 1. Checks which ports are exposed from the container by default. 1. Starts a special container that waits for these ports to be accessible. When the second stage of the check fails, either because there is no opened port in the service, or the service was not started properly before the timeout and the port is not responding, it prints the warning: `*** WARNING: Service XYZ probably didn't start properly`. In most cases it affects the job, but there may be situations when the job still succeeds even if that warning was printed. For example: - The service was started a little after the warning was raised, and the job is not using the linked service from the beginning. In that case, when the job needed to access the service, it may have been already there waiting for connections. - The service container is not providing any networking service, but it's doing something with the job's directory (all services have the job directory mounted as a volume under `/builds`). In that case, the service does its job, and since the job is not trying to connect to it, it does not fail. ### What services are not for As it was mentioned before, this feature is designed to provide **network accessible** services. A database is the simplest example of such a service. The services feature is not designed to, and does not add any software from the defined `services` image(s) to the job's container. For example, if you have the following `services` defined in your job, the `php`, `node` or `go` commands are **not** available for your script, and thus the job fails: ```yaml job: services: - php:7 - node:latest - golang:1.10 image: alpine:3.7 script: - php -v - node -v - go version ``` If you need to have `php`, `node` and `go` available for your script, you should either: - Choose an existing Docker image that contains all required tools. - Create your own Docker image, with all the required tools included and use that in your job. ### Accessing the services Let's say that you need a Wordpress instance to test some API integration with your application. You can then use for example the [tutum/wordpress](https://hub.docker.com/r/tutum/wordpress/) image in your `.gitlab-ci.yml`: ```yaml services: - tutum/wordpress:latest ``` If you don't [specify a service alias](#available-settings-for-services), when the job is run, `tutum/wordpress` is started and you have access to it from your build container under two hostnames to choose from: - `tutum-wordpress` - `tutum__wordpress` Hostnames with underscores are not RFC valid and may cause problems in 3rd party applications. The default aliases for the service's hostname are created from its image name following these rules: - Everything after the colon (`:`) is stripped. - Slash (`/`) is replaced with double underscores (`__`) and the primary alias is created. - Slash (`/`) is replaced with a single dash (`-`) and the secondary alias is created (requires GitLab Runner v1.1.0 or higher). To override the default behavior, you can [specify a service alias](#available-settings-for-services). ## Define `image` and `services` from `.gitlab-ci.yml` You can simply define an image that's used for all jobs and a list of services that you want to use during build time: ```yaml 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: ` (Same as using `` with the `latest` tag) - `image: :` - `image: @` It's also possible to define different images and services per job: ```yaml default: before_script: - bundle install test:2.6: image: ruby:2.6 services: - postgres:11.7 script: - bundle exec rake spec test:2.7: image: ruby:2.7 services: - postgres:12.2 script: - bundle exec rake spec ``` Or you can pass some [extended configuration options](#extended-docker-configuration-options) for `image` and `services`: ```yaml default: image: name: ruby:2.6 entrypoint: ["/bin/bash"] services: - name: my-postgres:11.7 alias: db-postgres entrypoint: ["/usr/local/bin/db-postgres"] command: ["start"] before_script: - bundle install test: script: - bundle exec rake spec ``` ## Passing environment variables to services You can also pass custom environment [variables](../variables/README.md) to fine tune your Docker `images` and `services` directly in the `.gitlab-ci.yml` file. For more information, see [custom environment variables](../variables/README.md#gitlab-ciyml-defined-variables) ```yaml # The following variables are automatically passed down to the Postgres container # as well as the Ruby container and available within each. variables: HTTPS_PROXY: "https://10.1.1.1:8090" HTTP_PROXY: "https://10.1.1.1:8090" POSTGRES_DB: "my_custom_db" POSTGRES_USER: "postgres" POSTGRES_PASSWORD: "example" PGDATA: "/var/lib/postgresql/data" POSTGRES_INITDB_ARGS: "--encoding=UTF8 --data-checksums" services: - name: postgres:11.7 alias: db entrypoint: ["docker-entrypoint.sh"] command: ["postgres"] image: name: ruby:2.6 entrypoint: ["/bin/bash"] before_script: - bundle install test: script: - bundle exec rake spec ``` ## Extended Docker configuration options > Introduced in GitLab and GitLab Runner 9.4. When configuring the `image` or `services` entries, you can use a string or a map as options: - when using a string as an option, it must be the full name of the image to use (including the Registry part if you want to download the image from a Registry other than Docker Hub) - when using a map as an option, then it must contain at least the `name` option, which is the same name of the image as used for the string setting For example, the following two definitions are equal: 1. Using a string as an option to `image` and `services`: ```yaml image: "registry.example.com/my/image:latest" services: - postgresql:9.4 - redis:latest ``` 1. Using a map as an option to `image` and `services`. The use of `image:name` is required: ```yaml image: name: "registry.example.com/my/image:latest" services: - name: postgresql:9.4 - name: redis:latest ``` ### Available settings for `image` > Introduced in GitLab and GitLab Runner 9.4. | Setting | Required | GitLab version | Description | |------------|----------|----------------| ----------- | | `name` | yes, when used with any other option | 9.4 |Full name of the image that should be used. It should contain the Registry part if needed. | | `entrypoint` | no | 9.4 |Command or script that should be executed as the container's entrypoint. It's translated to Docker's `--entrypoint` option while creating the container. The syntax is similar to [`Dockerfile`'s `ENTRYPOINT`](https://docs.docker.com/engine/reference/builder/#entrypoint) directive, where each shell token is a separate string in the array. | ### Available settings for `services` > Introduced in GitLab and GitLab Runner 9.4. | Setting | Required | GitLab version | Description | |------------|----------|----------------| ----------- | | `name` | yes, when used with any other option | 9.4 | Full name of the image that should be used. It should contain the Registry part if needed. | | `entrypoint` | no | 9.4 |Command or script that should be executed as the container's entrypoint. It's translated to Docker's `--entrypoint` option while creating the container. The syntax is similar to [`Dockerfile`'s `ENTRYPOINT`](https://docs.docker.com/engine/reference/builder/#entrypoint) directive, where each shell token is a separate string in the array. | | `command` | no | 9.4 |Command or script that should be used as the container's command. It's translated to arguments passed to Docker after the image's name. The syntax is similar to [`Dockerfile`'s `CMD`](https://docs.docker.com/engine/reference/builder/#cmd) directive, where each shell token is a separate string in the array. | | `alias` (1) | no | 9.4 |Additional alias that can be used to access the service from the job's container. Read [Accessing the services](#accessing-the-services) for more information. | (1) Alias support for the Kubernetes executor was [introduced](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/2229) in GitLab Runner 12.8, and is only available for Kubernetes version 1.7 or later. ### Starting multiple services from the same image > Introduced in GitLab and GitLab Runner 9.4. Read more about the [extended configuration options](#extended-docker-configuration-options). Before the new extended Docker configuration options, the following configuration would not work properly: ```yaml services: - mysql:latest - mysql:latest ``` The runner would start two containers using the `mysql:latest` image, but both of them would be added to the job's container with the `mysql` alias based on the [default hostname naming](#accessing-the-services). This would end with one of the services not being accessible. After the new extended Docker configuration options, the above example would look like: ```yaml services: - name: mysql:latest alias: mysql-1 - name: mysql:latest alias: mysql-2 ``` The runner still starts two containers using the `mysql:latest` image, however now each of them are also accessible with the alias configured in `.gitlab-ci.yml` file. ### Setting a command for the service > Introduced in GitLab and GitLab Runner 9.4. Read more about the [extended configuration options](#extended-docker-configuration-options). Let's assume you have a `super/sql:latest` image with some SQL database inside it and you would like to use it as a service for your job. Let's also assume that this image does not start the database process while starting the container and the user needs to manually use `/usr/bin/super-sql run` as a command to start the database. Before the new extended Docker configuration options, you would need to create your own image based on the `super/sql:latest` image, add the default command, and then use it in job's configuration, like: ```dockerfile # my-super-sql:latest image's Dockerfile FROM super/sql:latest CMD ["/usr/bin/super-sql", "run"] ``` ```yaml # .gitlab-ci.yml services: - my-super-sql:latest ``` After the new extended Docker configuration options, you can now simply set a `command` in `.gitlab-ci.yml`, like: ```yaml # .gitlab-ci.yml services: - name: super/sql:latest command: ["/usr/bin/super-sql", "run"] ``` As you can see, the syntax of `command` is similar to [Dockerfile's `CMD`](https://docs.docker.com/engine/reference/builder/#cmd). ### Overriding the entrypoint of an image > Introduced in GitLab and GitLab Runner 9.4. Read more about the [extended configuration options](#extended-docker-configuration-options). Before showing the available entrypoint override methods, let's describe shortly how the runner starts and uses a Docker image for the containers used in the CI jobs: 1. The runner starts a Docker container using the defined entrypoint (default from `Dockerfile` that may be overridden in `.gitlab-ci.yml`) 1. The runner attaches itself to a running container. 1. The runner prepares a script (the combination of [`before_script`](../yaml/README.md#before_script-and-after_script), [`script`](../yaml/README.md#script), and [`after_script`](../yaml/README.md#before_script-and-after_script)). 1. The runner sends the script to the container's shell STDIN and receives the output. To override the entrypoint of a Docker image, the recommended solution is to define an empty `entrypoint` in `.gitlab-ci.yml`, so the runner does not start a useless shell layer. However, that does not work for all Docker versions, and you should check which one your runner is using. Specifically: - If Docker 17.06 or later is used, the `entrypoint` can be set to an empty value. - If Docker 17.03 or previous versions are used, 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's `ENTRYPOINT`](https://docs.docker.com/engine/reference/builder/#entrypoint). Let's assume you have a `super/sql:experimental` image with some SQL database inside it and you would like 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. That means that when starting the container without additional options, it runs the database's process, while 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, and then using the new image in your CI job, you can now simply define an `entrypoint` in `.gitlab-ci.yml`. **For Docker 17.06+:** ```yaml image: name: super/sql:experimental entrypoint: [""] ``` **For Docker =< 17.03:** ```yaml image: name: super/sql:experimental entrypoint: ["/bin/sh", "-c"] ``` ## Define image and services in `config.toml` Look for the `[runners.docker]` section: ```toml [runners.docker] image = "ruby:latest" services = ["mysql:latest", "postgres:latest"] ``` The image and services defined this way are added to all job run by that runner. ## Define an image from a private Container Registry To access private container registries, the GitLab Runner process can use: - [Statically defined credentials](#using-statically-defined-credentials). That is, a username and password for a specific registry. - [Credentials Store](#using-credentials-store). For more information, see [the relevant Docker documentation](https://docs.docker.com/engine/reference/commandline/login/#credentials-store). - [Credential Helpers](#using-credential-helpers). For more information, see [the relevant Docker documentation](https://docs.docker.com/engine/reference/commandline/login/#credential-helpers). To define which should be used, the GitLab Runner process reads the configuration in the following order: - `DOCKER_AUTH_CONFIG` variable provided as either: - A [variable](../variables/README.md#gitlab-cicd-environment-variables) in `.gitlab-ci.yml`. - A project's variables stored on the projects **Settings > CI/CD** page. - `DOCKER_AUTH_CONFIG` variable provided as environment variable in `config.toml` of the runner. - `config.json` file placed in `$HOME/.docker` directory of the user running GitLab Runner process. If the `--user` flag is provided to run the GitLab Runner child processes as unprivileged user, the home directory of the main GitLab Runner process user is used. GitLab Runner reads this configuration **only** from `config.toml` and ignores it if it's provided as an environment variable. This is because GitLab Runner uses **only** `config.toml` configuration and does not interpolate **ANY** environment variables at runtime. ### Requirements and limitations - This feature requires GitLab Runner **1.8** or higher. - For GitLab Runner versions **>= 0.6, <1.8** there was a partial support for using private registries, which required manual configuration of credentials on runner's host. We recommend to upgrade your runner to at least version **1.8** if you want to use private registries. - Available for [Kubernetes executor](https://docs.gitlab.com/runner/executors/kubernetes.html) in GitLab Runner 13.1 and later. - [Credentials Store](#using-credentials-store) and [Credential Helpers](#using-credential-helpers) require binaries to be added to the GitLab Runner's `$PATH`, and require access to do so. Therefore, these features are not available on shared runners or any other runner where the user does not have access to the environment where the runner is installed. ### Using statically-defined credentials There are two approaches that you can take in order to access a private registry. Both require setting the environment variable `DOCKER_AUTH_CONFIG` with appropriate authentication information. 1. Per-job: To configure one job to access a private registry, add `DOCKER_AUTH_CONFIG` as a job variable. 1. Per-runner: To configure a runner so all its jobs can access a private registry, add `DOCKER_AUTH_CONFIG` to the environment in the runner's configuration. See below for examples of each. #### Determining your `DOCKER_AUTH_CONFIG` data As an example, let's assume that you want to use the `registry.example.com:5000/private/image:latest` image which is private and requires you to login into a private container registry. Let's also assume that these are the login credentials: | Key | Value | |:---------|:----------------------------| | registry | `registry.example.com:5000` | | username | `my_username` | | password | `my_password` | There are two ways to determine the value of `DOCKER_AUTH_CONFIG`: - **First way -** Do a `docker login` on your local machine: ```shell 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`: ```shell docker logout registry.example.com:5000 ``` - **Second way -** In some setups, it's possible that 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 need to prepare the required base64-encoded version of `${username}:${password}` and create the Docker configuration JSON manually. Open a terminal and execute the following command: ```shell # The use of "-n" - prevents encoding a newline in the password. echo -n "my_username:my_password" | base64 # Example output to copy bXlfdXNlcm5hbWU6bXlfcGFzc3dvcmQ= ``` Create the Docker JSON configuration content as follows: ```json { "auths": { "registry.example.com:5000": { "auth": "(Base64 content from above)" } } } ``` #### Configuring a job To configure a single job with access for `registry.example.com:5000`, follow these steps: 1. Create a [variable](../variables/README.md#gitlab-cicd-environment-variables) `DOCKER_AUTH_CONFIG` with the content of the Docker configuration file as the value: ```json { "auths": { "registry.example.com:5000": { "auth": "bXlfdXNlcm5hbWU6bXlfcGFzc3dvcmQ=" } } } ``` 1. You can now use any private image from `registry.example.com:5000` defined in `image` and/or `services` in your `.gitlab-ci.yml` file: ```yaml 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 `.gitlab-ci.yml`, 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, it is probably better to 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 makes registry changes and credential rotations much simpler. Of course 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: 1. Modify the runner's `config.toml` file as follows: ```toml [[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. 1. Restart the runner service. ### Using Credentials Store > Support for using Credentials Store was added in GitLab Runner 9.5. To configure credentials store, follow these steps: 1. To use a credentials store, you need an external helper program to interact with a specific keychain or external store. Make sure helper program is available in GitLab Runner `$PATH`. 1. Make GitLab Runner use it. There are two ways to accomplish this. Either: - Create a [variable](../variables/README.md#gitlab-cicd-environment-variables) `DOCKER_AUTH_CONFIG` with the content of the Docker configuration file as the value: ```json { "credsStore": "osxkeychain" } ``` - Or, if you're running self-managed runners, add the above JSON to `${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 want to use both images from private registry and public images from Docker Hub, pulling from Docker Hub would fail, because Docker daemon tries to use the same credentials for **ALL** the registries. ### Using Credential Helpers > Support for using Credential Helpers was added 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 which is private and requires you to log in into a private container registry. To configure access for `aws_account_id.dkr.ecr.region.amazonaws.com`, follow these steps: 1. Make sure `docker-credential-ecr-login` is available in GitLab Runner's `$PATH`. 1. Have any of the following [AWS credentials setup](https://github.com/awslabs/amazon-ecr-credential-helper#aws-credentials). Make sure that GitLab Runner can access the credentials. 1. Make GitLab Runner use it. There are two ways to accomplish this. Either: - Create a [variable](../variables/README.md#gitlab-cicd-environment-variables) `DOCKER_AUTH_CONFIG` with the content of the Docker configuration file as the value: ```json { "credHelpers": { "aws_account_id.dkr.ecr.region.amazonaws.com": "ecr-login" } } ``` This configures Docker to use the credential helper for a specific registry. or ```json { "credsStore": "ecr-login" } ``` This configures Docker to use the credential helper for all Amazon ECR registries. - Or, if you're running self-managed runners, add the above JSON to `${GITLAB_RUNNER_HOME}/.docker/config.json`. GitLab Runner reads this configuration file and uses the needed helper for this specific repository. 1. 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: ```yaml image: aws_account_id.dkr.ecr.region.amazonaws.com/private/image:latest ``` In the example above, 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 as described above. ## Configuring services Many services accept environment variables which allow you to easily change database names or set account names depending on the environment. GitLab Runner 0.5.0 and up passes all YAML-defined variables to the created service containers. For all possible configuration variables check the documentation of each image provided in their corresponding Docker hub page. All variables are passed to all services containers. It's not designed to distinguish which variable should go where. ### PostgreSQL service example See the specific documentation for [using PostgreSQL as a service](../services/postgres.md). ### MySQL service example See the specific documentation for [using MySQL as a service](../services/mysql.md). ## How Docker integration works Below is a high level overview of the steps performed by Docker during job time. 1. Create any service container: `mysql`, `postgresql`, `mongodb`, `redis`. 1. Create cache container to store all volumes as defined in `config.toml` and `Dockerfile` of build image (`ruby:2.6` as in above example). 1. Create build container and link any service container to build container. 1. Start build container and send job script to the container. 1. Run job script. 1. Checkout code in: `/builds/group-name/project-name/`. 1. Run any step defined in `.gitlab-ci.yml`. 1. Check exit status of build script. 1. Remove build container and all created service containers. ## How to debug a job locally The following commands are run without root privileges. You should be able to run Docker with your regular user account. First start with creating a file named `build_script`: ```shell cat < build_script git clone https://gitlab.com/gitlab-org/gitlab-runner.git /builds/gitlab-org/gitlab-runner cd /builds/gitlab-org/gitlab-runner make EOF ``` Here we use as an example the GitLab Runner repository which contains a Makefile, so running `make` executes the commands defined in the Makefile. Your mileage may vary, so instead of `make` you could run the command which is specific to your project. Then create some service containers: ```shell docker run -d --name service-mysql mysql:latest docker run -d --name service-postgres postgres:latest ``` This creates two service containers, named `service-mysql` and `service-postgres` which use the latest MySQL and PostgreSQL images respectively. They both run in the background (`-d`). Finally, create a build container by executing the `build_script` file we created earlier: ```shell docker run --name build -i --link=service-mysql:mysql --link=service-postgres:postgres ruby:2.6 /bin/bash < build_script ``` The above command creates a container named `build` that's spawned from the `ruby:2.6` image and has two services linked to it. The `build_script` is piped using STDIN to the bash interpreter which in turn executes the `build_script` in the `build` container. When you finish testing and no longer need the containers, you can remove them with: ```shell docker rm -f -v build service-mysql service-postgres ``` This forcefully (`-f`) removes the `build` container, the two service containers as well as all volumes (`-v`) that were created with the container creation.