GitLab SSH Access Configuration

[Mihai]

Overview:
This document describes the full process of configuring SSH access for a GitLab instance running inside a Docker container, behind an ISP router with dynamic IP, using Cloudflare DNS and a Cloudflare Tunnel for HTTPS.

Environment:

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GitLab Docker Image      | gitlab/gitlab-ce:18.10.0-ce.0
Container IP             | 172.0.1.10 (cloudflare_tunnel network)
Docker Host LAN IP       | 192.168.1.70
GitLab HTTPS URL         | https://gitlab.url.tld
SSH Subdomain            | ssh.gitlab.url.tld
ISP DDNS Hostname        | your-ddns-hostname.go.ro
SSH Port                 | 2224
Network                  | Behind ISP NAT router, dynamic public IP

Problem:
Git clone via SSH was not working. The GitLab container was only accessible via HTTPS through a Cloudflare Tunnel. Cloudflare Tunnel does not proxy raw TCP/SSH traffic, so SSH connections were timing out.

Root Causes:

• 1. expose in docker-compose.yml does not bind ports to the host - ports is required.

• 2. Cloudflare proxied DNS routes SSH traffic through Cloudflare, which drops raw TCP.

• 3. No ISP router port forwarding rule existed for port 2224.

• 4. Port mapping 2224:22 (GitLab SSH listens on port 22 inside the container)

Solution: Bypass Cloudflare for SSH
Use a dedicated subdomain ssh.code.scripting.ro with DNS only (no Cloudflare proxy), pointing to the real public IP via the ISP's DDNS hostname. SSH traffic goes directly to the server, bypassing Cloudflare entirely.

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Client
  └── ssh.gitlab.url.tld (CNAME → your-ddns-hostname.go.ro, DNS only)
        └── public IP (86.254.30.0) - YOUR ROUTER PUBLIC IP
              └── ISP Router (port forward 2224 → 192.168.1.70)
                    └── Docker host :2224
                          └── GitLab container :22

• Step 1 — Fix docker-compose.yml

Replace expose with ports and fix the port mapping:

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services:
  code:
    image: 'gitlab/gitlab-ce:18.10.0-ce.0'
    restart: always
    hostname: 'gitlab.url.tld'
    container_name: gitlab.url.tld
    tty: true
    environment:
      TZ: Europe/Bucharest
    ulimits:
      sigpending: 62793
      nproc: 131072
      nofile: 60000
      core: 0
    expose:
      - 443
    ports:
      - "2224:22"       # host:2224 → container:22 (GitLab SSH)
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - /apps/docker/docker-containers/gitlab.url.tld/config:/etc/gitlab
      - /apps/docker/docker-containers/gitlab.url.tld/logs:/var/log/gitlab
      - /apps/docker/docker-containers/gitlab.url.tld/data:/var/opt/gitlab
      - /apps/docker/docker-containers/gitlab.url.tld/hosts:/etc/hosts
      - /apps/docker/docker-containers/gitlab.url.tld/scripts-boot:/root/scripts-boot
    mac_address: 00:00:00:00:00:02
    networks:
      cloudflare_tunnel:
        ipv4_address: 172.0.1.10
    shm_size: '1024m'

networks:
  cloudflare_tunnel:
    external: true

volumes:
  code:
    driver: local

Restart the container:

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docker compose down && docker compose up -d

• Step 2 — Configure Cloudflare DNS

Add a CNAME record pointing ssh.gitlab.url.tld to the ISP DDNS hostname:

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Name               | Type  | Value                    | Proxy Status
ssh.gitlab.url.tld | CNAME | your-ddns-hostname.go.ro | ⬜ DNS only

Important: Proxy status must be DNS only (grey cloud). If proxied, Cloudflare will block raw TCP/SSH traffic.

• Step 3 — ISP Router Port Forwarding

Log into the ISP router and add a port forwarding rule:

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Name         | GitLab SSH
Protocol     | TCP
WAN Port     | 2224
LAN Host IP  | 192.168.1.70 (Docker host)
LAN Port     | 2224

• Step 4 — Configure gitlab.rb

Edit: gitlab.rb and modify the following fields:

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external_url 'https://gitlab.url.tld'
# SSH configuration
gitlab_rails['gitlab_shell_ssh_host'] = 'ssh.gitlab.url.tld'
gitlab_rails['gitlab_shell_ssh_port'] = 2224

Reconfigure GitLab:

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docker exec -it container_name gitlab-ctl reconfigure

Restart GitLab:

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docker exec -it container_name gitlab-ctl restart

Refresh the GitLab page and check Clone with SSH.