About service containers

About service containers

Service containers are Docker containers that provide a simple and portable way for you to host services that you might need to test or operate your application in a workflow. For example, your workflow might need to run integration tests that require access to a database and memory cache.

You can configure service containers for each job in a workflow. GitHub creates a fresh Docker container for each service configured in the workflow, and destroys the service container when the job completes. Steps in a job can communicate with all service containers that are part of the same job. However, you cannot create and use service containers inside a composite action.

Communicating with service containers

You can configure jobs in a workflow to run directly on a runner machine or in a Docker container. Communication between a job and its service containers is different depending on whether a job runs directly on the runner machine or in a container.

Running jobs in a container

When you run jobs in a container, GitHub connects service containers to the job using Docker's user-defined bridge networks. For more information, see "Use bridge networks" in the Docker documentation.

Running the job and services in a container simplifies network access. You can access a service container using the label you configure in the workflow. The hostname of the service container is automatically mapped to the label name. For example, if you create a service container with the label redis, the hostname of the service container is redis.

You don't need to configure any ports for service containers. By default, all containers that are part of the same Docker network expose all ports to each other, and no ports are exposed outside of the Docker network.

Running jobs on the runner machine

When running jobs directly on the runner machine, you can access service containers using localhost:<port> or 127.0.0.1:<port>. GitHub configures the container network to enable communication from the service container to the Docker host.

When a job runs directly on a runner machine, the service running in the Docker container does not expose its ports to the job on the runner by default. You need to map ports on the service container to the Docker host. For more information, see "Mapping Docker host and service container ports."

Creating service containers

You can use the services keyword to create service containers that are part of a job in your workflow. For more information, see jobs.<job_id>.services.

This example creates a service called redis in a job called container-job. The Docker host in this example is the node:16-bullseye container.

name: Redis container example
on: push

jobs:
  # Label of the container job
  container-job:
    # Containers must run in Linux based operating systems
    runs-on: ubuntu-latest
    # Docker Hub image that `container-job` executes in
    container: node:16-bullseye

    # Service containers to run with `container-job`
    services:
      # Label used to access the service container
      redis:
        # Docker Hub image
        image: redis

Mapping Docker host and service container ports

If your job runs in a Docker container, you do not need to map ports on the host or the service container. If your job runs directly on the runner machine, you'll need to map any required service container ports to ports on the host runner machine.

You can map service containers ports to the Docker host using the ports keyword. For more information, see jobs.<job_id>.services.

When you map ports using the ports keyword, GitHub uses the --publish command to publish the container’s ports to the Docker host. For more information, see "Docker container networking" in the Docker documentation.

When you specify the Docker host port but not the container port, the container port is randomly assigned to a free port. GitHub sets the assigned container port in the service container context. For example, for a redis service container, if you configured the Docker host port 5432, you can access the corresponding container port using the job.services.redis.ports[5432] context. For more information, see "Contexts."

Example mapping Redis ports

This example maps the service container redis port 6379 to the Docker host port 6379.

name: Redis Service Example
on: push

jobs:
  # Label of the container job
  runner-job:
    # You must use a Linux environment when using service containers or container jobs
    runs-on: ubuntu-latest

    # Service containers to run with `runner-job`
    services:
      # Label used to access the service container
      redis:
        # Docker Hub image
        image: redis
        #
        ports:
          # Opens tcp port 6379 on the host and service container
          - 6379:6379

Further reading

• "Creating Redis service containers"
• "Creating PostgreSQL service containers"