Tips and Tricks #175: Implement Trunk-Based Development with Feature Flags

Ship code continuously while controlling feature rollout with runtime flags.

Code Snippet

# feature_flags.py
import os
from functools import wraps

class FeatureFlags:
    def __init__(self):
        self._flags = {
            "new_checkout": os.getenv("FF_NEW_CHECKOUT", "false") == "true",
            "dark_mode": os.getenv("FF_DARK_MODE", "false") == "true",
        }
    
    def is_enabled(self, flag: str) -> bool:
        return self._flags.get(flag, False)

flags = FeatureFlags()

# Usage in code
def get_checkout_page():
    if flags.is_enabled("new_checkout"):
        return render_new_checkout()
    return render_legacy_checkout()

Why This Helps

• Enables continuous deployment without feature branches
• Instant rollback by toggling flag
• Gradual rollout to percentage of users

How to Test

• Toggle flag and verify behavior change
• Test both code paths in CI

When to Use

Large features, risky changes, A/B testing, gradual rollouts.

Performance/Security Notes

Clean up old flags regularly. Consider using a feature flag service for complex scenarios.

References

• https://martinfowler.com/articles/feature-toggles.html

Try this tip in your next project and share your results in the comments!