It's available on GitHub at https://github.com/dwwoelfel/latch

It has a self-hosted UI that reads and writes directly to Google storage and a nodejs client that subscribes to flag changes via Google Pub/Sub.

I made a short video walkthrough to help give a feel for the UI:

https://www.youtube.com/watch?v=GKDekwvPTD4

In the past I've stored feature flags directly in the database, but I wanted something that was more consistent between environments. I also want to be able to use feature flags to trigger db failover during upgrades, so storing them in the db was out.

I've also used two of the main SaaS services at a previous company, which made me wary of lock-in and performance issues.

Google Storage turned out to be well-suited for feature flags. It has a pub/sub integration where changes to a bucket trigger notifications in pub/sub. It has object versioning, which I use to display a flag history. It has an increasing "generation" id for each file, which I use to prevent race conditions and ensure that I'm not making changes based on stale information.

I'm pretty happy with the UI. I built a Relay-compatible GraphQL interface over Google Storage and the UI uses that to read and write from storage using OAuth credentials. If I want to give someone access to the feature flags, I just have to manage their permissions to the bucket.