Gitlab self hosted: Trigger 422 Error

[Romain_LEGUAY]

Describe the problem/error/question

Hi,
I try to configure Gitlab (self hosted with no external access possible but with valid SSL certificate). I succeed to authenticate with the service either with Access Token or with OAuth 2.0 method.

The error happen when I try to create a Gitlab Issue trigger.

The communication between our Gitlab server and n8n server works.

What is the error message (if any)?

When I try to create a Issue trigger, I have the following message:

Problem running workflow
Your request is invalid or could not be processed by the service

Show Details
GitLab Trigger: 422 - {"error":"Invalid url given"} - Invalid url given

Please share your workflow

Share the output returned by the last node

No output

Information on your n8n setup

• n8n version: 1.29.1
• Database (default: SQLite): SQLite
• n8n EXECUTIONS_PROCESS setting (default: own, main):
• Running n8n via (Docker, npm, n8n cloud, desktop app): docker compose with traefik (SSL credentials valid)
• Operating system:: ubuntu 20.04

[Romain_LEGUAY]

So I continue to investigate on my problem.
I found out that if I launch the docker compose with start --tunnel command (inside the docker-compose file), the service works normaly.
I think it’s an issue on my side for the configuration but I don’t know what I do wrong. I tried to modify the different environment variable N8N_HOST and WEBHOOK_URL but nothing change.

I join you part of the docker-compose.

n8n:
    image: docker.n8n.io/n8nio/n8n:1.29.1
    restart: always
    ports:
      - "127.0.0.1:5678:5678"
    labels:
      - traefik.enable=true
      - traefik.http.routers.n8n.rule=Host(`${DOMAIN_NAME}`)
      - traefik.http.routers.n8n.tls=true
      - traefik.http.routers.n8n.entrypoints=web,websecure
      - traefik.http.routers.n8n.tls.certresolver=ovh
      - traefik.http.middlewares.n8n.headers.SSLRedirect=true
      - traefik.http.middlewares.n8n.headers.STSSeconds=315360000
      - traefik.http.middlewares.n8n.headers.browserXSSFilter=true
      - traefik.http.middlewares.n8n.headers.contentTypeNosniff=true
      - traefik.http.middlewares.n8n.headers.forceSTSHeader=true
      - traefik.http.middlewares.n8n.headers.SSLHost=${DOMAIN_NAME}
      - traefik.http.middlewares.n8n.headers.STSIncludeSubdomains=true
      - traefik.http.middlewares.n8n.headers.STSPreload=true
      - traefik.http.routers.n8n.middlewares=n8n@docker
    environment:
      - N8N_HOST=${DOMAIN_NAME}
      - N8N_PORT=5678
      - N8N_PROTOCOL=https
      - NODE_ENV=production
      - WEBHOOK_URL=https://${DOMAIN_NAME}
      - GENERIC_TIMEZONE=${GENERIC_TIMEZONE}
      - N8N_LOG_LEVEL=debug
    volumes:
      - n8n_data:/home/node/.n8n

Does anyone have the same issue?

[Romain_LEGUAY]

I found the issue: The problem is on Gitlab configuration side. By default, Gitlab does not accept webhooks from local network. You can activate it from the Gitlab Administration side like this: Admin → Settings → Network → Outbound Requests → Allow requests to the local network from hooks and services
The explination can be found here