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Feature Flags

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Feature flags control when features become available to users. Code is deployed with features disabled, then enabled gradually via runtime configuration.

This is a Stage 12 (Release Toggling) concern - distinct from deployment (Stage 10).

Flag Lifecycle

Phase Duration Actions
Create Day 0 Add flag, deploy code with feature OFF
Enable Days 1-14 Gradual rollout (10% → 50% → 100%)
Stabilize Days 15-30 Monitor, collect feedback
Remove Days 30-90 Delete flag and old code paths

Rollout Strategies

Percentage rollout:

Day Percentage Validation
1 10% Monitor errors
3 25% Check business metrics
7 50% Validate performance
14 100% Full rollout

User-targeted: Enable for specific users, groups, or beta testers.

Time-based: Enable during specific time windows (e.g., Black Friday sale).

Disabling Features

When issues occur, disable instantly via API or dashboard. This is not a rollback - the code remains deployed, only the feature is turned off.

Action What happens Time
Disable flag Feature hidden from users Seconds
Deployment rollback Previous code version restored Minutes

Removing Flags

When: Feature stable 30+ days, 100% rollout complete, no issues.

Steps:

  1. Verify stability (30 days, no issues)
  2. Remove old code path
  3. Remove flag checks
  4. Remove flag definition
  5. Deploy cleanup

Flag Hygiene

Anti-Pattern Problem Solution
Nested flags Complex logic Flatten or combine
Permanent flags Technical debt Enforce cleanup deadlines
Missing owners Nobody responsible Require owner in definition
No monitoring Can't detect issues Add metrics per flag

External Resources

Next Steps

Tutorials | How-to Guides | Explanation | Reference

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