Skip to content

Feature Flags

Home › Explanation › Continuous Delivery › Deployment › Feature Flags

How to implement, operate, and retire feature flags.

Flag Lifecycle

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

Creating a Flag

Step 1: Define the Flag

# flags.yaml
features:
  new-checkout:
    description: "New checkout flow with one-click purchase"
    owner: "checkout-team"
    created: "2024-01-15"
    cleanup_deadline: "2024-04-15"
    enabled: false

Step 2: Implement in Code

func processCheckout(user User) {
    if featureFlags.IsEnabled("new-checkout", user) {
        newCheckoutFlow(user)
    } else {
        legacyCheckoutFlow(user)
    }
}

Step 3: Deploy

Deploy with flag OFF. Code reaches production but feature is not active.

Enabling a Flag (Rollout)

Simple Boolean

new-checkout:
  enabled: true

Percentage Rollout

new-checkout:
  enabled: true
  rollout_percentage: 10  # Start with 10%

Increase gradually:

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

User-Targeted Rollout

new-checkout:
  enabled_for_users:
    - "beta@example.com"
    - "tester@example.com"
  enabled_for_groups:
    - "beta-testers"
    - "internal-users"

Time-Based Flag

black-friday-sale:
  enabled_after: "2024-11-29T00:00:00Z"
  enabled_before: "2024-12-02T00:00:00Z"

Monitoring Flags

Track key metrics per flag:

Metric Flag OFF Flag ON Action
Error rate 0.1% 0.5% Investigate
Latency P95 100ms 150ms Acceptable
Conversion 2.5% 2.8% Success!

Emergency Disable

When issues occur:

# Instant disable
curl -X PUT https://flags.example.com/api/flags/new-checkout \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"enabled": false}'

Or through UI dashboard.

Removing Flags

When to Remove

  • Feature stable for 30+ days
  • 100% rollout complete
  • No issues or rollbacks needed
  • Business metrics validated

Cleanup Steps

  1. Verify stability - No issues for 30 days
  2. Remove old code path - Delete legacy implementation
  3. Remove flag checks - Delete conditional logic
  4. Remove flag definition - Delete from configuration
  5. Deploy cleanup - Single commit removing all traces

Example Cleanup Commit

chore(checkout): remove new-checkout feature flag

Feature has been stable at 100% for 45 days.
Removing flag and legacy checkout code.

- Remove feature flag checks from checkout.go
- Delete legacy_checkout.go
- Remove flag from flags.yaml
- Update tests

Relates to #456

Flag Hygiene

Track Flag Age

Flag Created Age Status
new-checkout 2024-01-15 45 days Ready for cleanup
beta-dashboard 2024-02-01 30 days Monitoring
experiment-a 2023-10-01 120 days OVERDUE

Enforce Cleanup Deadlines

new-checkout:
  cleanup_deadline: "2024-04-15"
  owner: "checkout-team"

Alert when deadline approaches or passes.

Anti-Patterns to Avoid

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

Next Steps

Tutorials | How-to Guides | Explanation | Reference

You are here: Explanation — understanding-oriented discussion that clarifies concepts.