Ten Notes on Feature Flags

Naming things well saved us more time than any framework migration. Most production incidents start as a small assumption nobody wrote down. We measured first, and the bottleneck was not where anyone expected.

Lessons

Latency percentiles tell a story that averages politely hide. Small pull requests get real reviews, large ones get approvals. The rollback plan should exist before the rollout plan is approved.

Most production incidents start as a small assumption nobody wrote down. We measured first, and the bottleneck was not where anyone expected.

Trade-offs

Logs answer questions you knew to ask; traces answer the ones you did not. Every retry needs a budget, otherwise it is just a slower outage. We wrote the migration twice: once to learn, once to ship. The best architecture diagram is the one the new hire can redraw from memory.

• Write the failure mode down before writing code
• Delete dead code the same week
• Keep migrations reversible
• Alert on symptoms, not causes

We measured first, and the bottleneck was not where anyone expected. Every retry needs a budget, otherwise it is just a slower outage.

Getting started

Caches are easy to add and surprisingly hard to remove. Our on-call rotation improved the day we deleted half of the alerts. Feature flags are debt with an expiration date you must actually enforce.

Naming things well saved us more time than any framework migration. Latency percentiles tell a story that averages politely hide.

Our on-call rotation improved the day we deleted half of the alerts. Logs answer questions you knew to ask; traces answer the ones you did not.