This doesn't need to be on the same instance as you're deploying to - in fact it shouldn't be. For the purposes of this prototype I did re-use the same instance. You could split to a second instance if you want.
SSH into the instance you're going to host the Gitlab CI runner on.
Install Docker
We're following the Docker documentation for install Docker Engine on Ubuntu here.
sudo apt-get remove docker docker-engine docker.io containerd runc
sudo apt-get install \
ca-certificates \
curl \
gnupg \
lsb-release
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
echo \
"deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
$(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-compose-plugin
sudo usermod -a -G docker ubuntu
Log out and back in to get the new group docker for your user. Test Docker.
$ docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
2db29710123e: Pull complete
Digest: sha256:18a657d0cc1c7d0678a3fbea8b7eb4918bba25968d3e1b0adebfa71caddbc346
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
Great, that worked.
Install & run Gitlab Runner
Now we're going to follow Gitlab's run Gitlab Runner in a container docs.
You might want to put the configuration directory somewhere other than /etc/gitlab-runner, up to you.
$ sudo mkdir /etc/gitlab-runner
$ docker run -d --name gitlab-runner --restart always \
-v /etc/gitlab-runner:/etc/gitlab-runner \
-v /var/run/docker.sock:/var/run/docker.sock \
gitlab/gitlab-runner:latest
Obtain a registration key from your Gitlab instance and register the runner (docs) with your Gitlab instance.
$ docker run --rm -it -v /etc/gitlab-runner:/etc/gitlab-runner gitlab/gitlab-runner register
Runtime platform arch=amd64 os=linux pid=6 revision=0d4137b8 version=15.5.0
Running in system-mode.
Enter the GitLab instance URL (for example, https://gitlab.com/):
https://gitlab.example.org
Enter the registration token:
GR123456abcdefg-dddddEEEEEfff
Enter a description for the runner:
[123abc456def]: deploy-runner
Enter tags for the runner (comma-separated):
docker
Enter optional maintenance note for the runner:
Registering runner... succeeded runner=GR123456abcdefg-x
Enter an executor: docker, shell, virtualbox, docker+machine, docker-ssh+machine, custom, docker-ssh, parallels, ssh, instance, kubernetes:
docker
Enter the default Docker image (for example, ruby:2.7):
alpine:latest
Runner registered successfully. Feel free to start it, but if it's running already the config should be automatically reloaded!
Configuration (with the authentication token) was saved in "/etc/gitlab-runner/config.toml"
Once your runner shows up as connected in Gitlab on Settings > CI > Runners, you can move on to configure a deployment pipeline from CI to webserver.