<< back to Guides

🚩 Deep Dive into Feature Flags

Feature flags (also known as feature toggles) allow teams to turn features on or off at runtime without deploying new code. They are critical for continuous delivery, experimentation, and safe deployments.

---

🎯 What Are Feature Flags?

Feature flags are conditional statements in code that control the availability of features.

if (featureFlags.newCheckoutFlow) {
  renderNewCheckout();
} else {
  renderOldCheckout();
}

---

🧰 Types of Feature Flags

1. Release Flags

Used to deploy incomplete or risky features safely.

• Enable a feature for internal users or beta testers.
• Gradually roll out a new feature to users.

2. Experiment Flags (A/B Testing)

Used to measure the performance or behavior of variants.

• Compare “Feature A” vs. “Feature B” in production.
• Integrates well with analytics tools.

3. Ops Flags

Enable or disable infrastructure or operational behavior.

• Toggle log levels, enable debug mode, etc.
• Control circuit breakers or database fallbacks.

4. Permission Flags

Used for role-based or user-specific access.

• Enable premium features for paid users only.
• Enable admin-only features.

5. Kill Switch Flags

Instantly disable broken or risky features.

• Emergency toggle to turn off a feature causing issues.

---

⚙️ How Feature Flags Work

Flags are typically defined in:

• Config files
• Environment variables
• Remote config services (LaunchDarkly, Unleash, Flagsmith)

They may be evaluated:

• At build-time (compile-time)
• At runtime (client/server-side)
• Based on context (user role, geolocation, etc.)

---

🌐 Architecture and Storage

Feature flags can be stored in:

• JSON/YAML files
• In-memory cache
• Remote config services with SDKs
• Feature management platforms

// Example: Remote flag check
const flag = await getFlag('newSearchBar');
if (flag.enabled) showNewSearch();

---

🧪 Best Practices

✅ Use descriptive flag names

• e.g., enableAdvancedFilters, not flag123

✅ Clean up stale flags

• Prevent "flag debt" (unused toggles that clutter code)

✅ Keep flag logic simple

• Avoid deeply nested conditions with multiple flags

✅ Audit flag usage

• Know who owns each flag and why it exists

✅ Test both sides of a flag

• Ensure feature on and off paths are covered

---

🔥 Anti-Patterns to Avoid

🚫 Using flags as permanent config

• Long-lived flags become hidden config values

🚫 Too many flags in the same module

• Leads to combinatorial explosion and logic complexity

🚫 Not versioning flags

• Changing meaning over time without tracking can cause regressions

---

🚀 Tools & Services

Tool	Type	Notes
LaunchDarkly	Commercial SaaS	Powerful targeting, auditing, SDK support
Unleash	Open-source	Self-hosted, SDKs in many languages
Flagsmith	Open-source + SaaS	Hybrid deployment support
ConfigCat	SaaS	Easy-to-use UI, targeting rules
Split.io	Commercial	A/B testing and flag management

---

👷 Use Cases

• Progressive delivery of features
• Canary releases with staged rollouts
• Blue/green deployments
• A/B testing and experimentation
• Hotfixes without deploying

---

📌 Summary

• Feature flags decouple deployment from release.
• They enable faster iteration, safer rollouts, and targeted experimentation.
• Clean-up and good governance are critical to avoiding tech debt.

<< back to Guides