Using Feature Flags to Avoid Downtime During Migrations

At AWS re:Invent 2021, LaunchDarkly engineers Mike Zorn and Justin Caballero presented techniques for painless migration using feature flags. They demonstrated how to convert a streaming event architecture and migrate production databases with zero downtime through gradual, reversible, and verifiable processes controlled by feature flags. The talk covered two examples of larger migrations undertaken at LaunchDarkly: the migration of a high-throughput data processing system and the migration of their core data store. Feature flags were used to change runtime behavior without any other modification, allowing for low latency updates and enabling additional use cases such as monitoring fidelity changes and handling migrations safely while mitigating risks.