How to use Drone runner with Gitlab and DRONE_RUNNER_CAPACITY > 1?

Development
1

I’m using Drone server and docker runner with the following configuration:

services:
  drone:
    image: drone/drone:2.17
    container_name: drone-srv
    restart: always
    ports:
      - "5100:80"
    volumes:
      - /var/lib/drone:/data
    environment:
      DRONE_GITLAB_SERVER: <server>
      DRONE_GITLAB_CLIENT_ID: <client_id>
      DRONE_GITLAB_CLIENT_SECRET: <secret>
      DRONE_GITLAB_SKIP_VERIFY: "true"
      DRONE_RPC_SECRET: <secret>
      DRONE_SERVER_HOST: <host>
      DRONE_SERVER_PROTO: https
      DRONE_USER_CREATE: username:admin,admin:true
      DOCKER_API_VERSION: 1.39
  runner:
    image: drone/drone-runner-docker:1.8
    container_name: drone-runner
    restart: always
    ports:
      - "5110:3000"
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    environment:
      DRONE_RPC_PROTO: https
      DRONE_RPC_HOST: <host>
      DRONE_RPC_SECRET: <secret>
      DRONE_RUNNER_CAPACITY: 5
      DRONE_RUNNER_NAME: drone-docker-runner-1
      DRONE_RUNNER_ENVIRON: GIT_SSL_NO_VERIFY:false

GitLab version is 16.0.

When having DRONE_RUNNER_CAPACITY>1, the runners can’t use GitLab OAuth correctly: pipelines are stuck and I get plenty of messages in the runner log, like the following:

time="2023-06-20T07:27:05Z" level=error msg="cannot get stage details" error="The provided authorization grant is invalid, expired, revoked, does not match the redirection URI used in the authorization request, or was issued to another client." stage.id=7170 stage.name="..." stage.number=1 thread=5

With DRONE_RUNNER_CAPACITY=1 everything works like a charm. However, I’d like to increase the capacity. Could you please advise?

It feels like multiple threads (when capacity is higher than 1) are using the same authorization grant and somehow interfering with each other. As a result, only one thread is actually working and others are failed with the mentioned authorization error and therefore get stuck.