Type-safe feature flagging in openfeature: Lessons learned from using feature flags at google

Featureflags?

• Idea: Change the behaviour of an application without rebuilding it
• Goal: Control rollout, reduce risk, experiment (a/b)
• At google: A huge number of feature flags (150k+) but that’s because people forget to turn them off

Where does the flag come from

• Lifecycle of a flag: Create, Manage, Deprecate, Delete -> But will it be created frist in code or in the service
• Classic implementation: Just a if/else that uses a function to get the flag
• Problem: What if the flag names missmatch between the code and flag ser -> Muliple sources of truth
• Solution: Require use of auto-generated flag bindings (codegen from the management system) to mitigate typos, etc.

OpenFeature

• Goal: Vendor agnostic, standardized, open source
• Basic setup: Register provider (once per app), create a client, use client to get flags
• CLI: Integrate into management system, keep a local manifest of all flags and generate code (generates the client)
• Now: Just call the client’s method instead of hard-coding feature flag names