Maintenance Mode

GitLab (fewer requirements)
GitLab (maintenance mode allows read access)
Minimum hardware requirements: 4 vCPU and 4 GB RAM support up to 500 users. No specific recommendation for disk size.
GitLab has a maintenance mode, which blocks all external actions that change its internal state. There are three ways to enable maintenance mode: web UI, API and Rails console.
Supporting up to 3000 users, requires 8 vCPUs, 48 GB RAM, 300 GB attached storage, 200 GB root storage.
GitHub has a maintenance mode, takes the GitHub Enterprise Server instance offline and users can’t access it. Use the Management Console.