A release platform on a fork of Unleash
A fork of Unleash that became a bank's release platform: seven teams at the start, about fifty by the end.
Unleash out of the box covers flag switching and gradual rollouts. What isn't in the box starts right after: who is allowed to touch a flag in production, how you describe a segment more complex than «ten percent of users», and what a team does when it doesn't want to write polling and caching again in every service. The SDK came out of that last question.
Technically not much of it was hard. Getting people to agree was. The first seven teams came on their own, they wanted gradual rollouts. The rest followed once the pipeline started asking why a change was shipping without a flag, and the DORA dashboard showed whose change failure rate was higher than the team next door.
Backstage went on top: a service catalogue, CI/CD status and DORA metrics in one place. Leadership stopped asking for reports and started opening a dashboard. That was most of the point. Onboarding a new engineer dropped to about two working days.
The code was the easy part. Flag hygiene is the hard one, and it is the thing nobody warns you about: teams add flags happily and never delete them, and a year later you're reading conditionals nobody can explain. If I built it again, every temporary flag would have an owner and an expiry date from day one, and the platform would nag people about the expired ones.