Upgrading GitLab CE v12 to v18: The SSH Surprise That Almost Ruined Everything

Jan 15 · 10 min read · 40 hours. 24 upgrade steps. 100+ repositories. Zero data loss. I thought I was done. It was Monday morning, 9 AM. I'd been working since Friday night - a weekend marathon through 22 GitLab versions and 2 OS migrations. Every check passed: GitLab vers...