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How to create own GitLab Runner on Ubuntu

Sources:

NOTE: For run commands become root or use sudo (not included in text).

Install Docker

Get Ubuntu virtual machine.

apt update

apt install curl gnupg ca-certificates

Add apt sources:

install -m 0755 -d /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | gpg --dearmor -o /etc/apt/keyrings/docker.gpg
chmod a+r /etc/apt/keyrings/docker.gpg
echo "deb [arch=amd64 signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu jammy stable" | tee /etc/apt/sources.list.d/docker.list
apt update
apt install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Verify it is working: docker run hello-world

Install Runner

Add apt sources: curl -L "https://packages.gitlab.com/install/repositories/runner/gitlab-runner/script.deb.sh" | sudo bash

apt install gitlab-runner

Verify it is working:

gitlab-runner -version
gitlab-runner status

Add runner to Gitlab and register runner

Source https://docs.gitlab.com/ee/ci/runners/register_runner.html

Go to Gitlab and ... On the top bar, select Main menu > Groups and find your group. On the left sidebar, select CI/CD > Runners. Select New group runner. Select a platform. Optional. Enter configurations for the runner. Select Submit.

You get CLI command which must be run on runner's machine.

eg. gitlab-runner register --url https://gitlab.com --token xxxxx

After running the command, a few questions must be answered.

Runner and job tags

When you added runner into Gitlab you could set tags which define runner's ability (kind of OS, compiler version etc.)

You can mark pipeline job to match runner's tag like this ...

image: golang:latest

compile:
  tags:
    - runner1
  stage: build
  script:
    - pwd

You can verify that workload really do on new runner by checking job output

...
Preparing environment
Running on runner-imchus3qc-project-34891567-concurrent-0 via runner1...
...

The important part is "via runner1".

Using runner in multiple groups and projects

One runner can be used by multiple groups and projects but each time must be registered again.

IPv6 in docker

Enable in Docker

  • Create file daemon.json if not exist touch /etc/docker/daemon.json
  • Make content of file
{
  "ipv6": true,
  "fixed-cidr-v6": "2001:470:6f:4ee:1::/80"
}
  • Restart service systemctl restart docker
  • Check network interface docker0 ... should have IPv6 address

Sources:

Enable in Runner

  • Find file /etc/gitlab-runner/config.toml
  • Add enable_ipv6 = true into section [runners.docker]
  • Restart service systemctl restart gitlab-runner
  • Verify IPv6 address in docker docker run -it ubuntu bash -c "ip -6 addr show dev eth0; ip -6 route show"
  • Check sysctl net.ipv6.conf.default.forwarding should be 1
  • Check sysctl net.ipv6.conf.all.forwarding should be 1
  • Check route table route -6n should be there route 2001:470:6f:4ee:1::/80 to dev docker0

Runner config for example:

concurrent = 1
check_interval = 0
shutdown_timeout = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "runner1"
  url = "https://gitlab.com"
  id = 111
  token = "xxxxx"
  token_obtained_at = 2023-05-11T19:09:58Z
  token_expires_at = 0001-01-01T00:00:00Z
  executor = "docker"
  [runners.cache]
    MaxUploadedArchiveSize = 0
  [runners.docker]
    tls_verify = true
    image = "golang:latest"
    privileged = false
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache"]
    shm_size = 0
    enable_ipv6 = true

Comment from source code:
To enable IPv6 support for this network, set enable_ipv6 to true inside the Docker config. This feature works only when the Docker daemon is configured with IPv6 enabled. To enable IPv6 support on your host, see the Docker documentation.

Source: https://gitlab.com/gitlab-org/gitlab-runner/-/commit/01dfa2b05741960888a78a2a110b8cf1ef0d7afb

Let neighbors know where to find dockers

Now should works ping between Docker host and Docker guest network interface. The trouble is nobody knows about this network. It is resulting in the state when packets go out but never come back (they do not know where).

There are two ways ... use NDP proxying or distribute route using "Router Advertisement"(RA)

I choose Router Advertisement

  • Create config file touch /etc/radvd.conf
  • Make content of file
interface ens18 {
    AdvSendAdvert on;
    AdvDefaultLifetime 0;
    MinRtrAdvInterval 30;
    MaxRtrAdvInterval 100;

    route 2001:470:6f:4ee:1::/80 {
        AdvRouteLifetime 6000;
    };
};
  • Install RA daemon apt install radvd
  • Check route tables on others computers ... should be there route "2001:470:6f:4ee:1::/80" to gateway "Docker host IP"
  • Manually add route "2001:470:6f:4ee:1::/80" to "Docker host IP" into the (Mikrotik) router (it doesn't load RA I don't know why)

Sources:

Not used but can be handy:
In case sysctl net.ipv6.conf.eth0.accept_ra get 1 then should be set to 2 to awoid collision during using ipv6 forwarding and also use ipv6 SLAAC. Changing it to 1 will allow you to automatically get a ipv6 Global or ULA address, ONLY if ipv6 forwarding is set to 0.