Mastering Feature Flags: Best Practices and Implementation with Firebase Remote Config

Feature flags are a powerful tool that makes building and releasing mobile apps both safer and faster. Developers and teams can merge code faster and release more often, without having to worry about breaking something. Additionally, it allows the team to target specific users and to experiment via A/B testing.

We will take a closer look at what feature flags are, how they can help us, best practices, and how to start using them in your project by leveraging the Firebase Remote Config cloud service.

Transcript

1. Mastering Feature Flags Best Practices and Implementation with Firebase Remote Config Domen Lanišnik Android Engineer, Lyft
2. Agenda • Basics • Benefits and drawbacks • Best practices • Advanced uses • Getting started with Firebase Remote Config • Summary
3. What is a Feature Flag • Simple boolean variable • Control remotely whether a feature is enabled • No need to rebuild and re-release the app Feature Flag Turned OFF Feature Flag Turned ON
4. What is a Feature Flag if (isFeatureEnabled("shareFeatureEnabled")) { // show Share button } if (isFeatureEnabled("useNewComposeScreen")) { // open new Compose based screen } else { // open old View based screen }
5. Why Use Feature Flags • Protect against critical bugs or crashes • Decouple from the release process • Control which users get the feature • Avoid long-lived feature branches • Support one-time features • Run A/B experiments
6. What to Watch Out For • Overusing feature flags (complexity) • Dependant feature flags • Increased testing difficulty • Stale feature flags (tech debt)
7. Best Practices • Put new features under feature flags and ship early • Have a clear naming convention • Define ownership • Perform regular reviews for stale flags • Avoid dependent flags
8. Different Types of Feature Flags • Int, String, Double, Lists, Json, … • Allows for different configurations • Enables experimenting with different values
9. Kill Switches • Used for critical paths • Refreshed often • Disable an important feature in case of an issue • Should not be same as the main feature flag
10. A/B Testing • Divide the user base into two groups • Gather analytics and metrics • Decide whether to ship the new feature
11. How to Start Using Feature Flags • Implement your own feature management service • Use existing open-source libraries • Use a third-party feature management service
12. Firebase Remote Config • Cloud service for changing behavior and appearance of apps • Third-party feature management service • Offers everything out-of-the-box • Update values through console or backend APIs • Android, iOS, Flutter, Web, and Backend
13. Implementation Steps 1. Set up (new) Firebase Project 2. Integrate Firebase SDKs into your app 3. Configure the Remote Config object 4. Fetch and activate values 5. Read values from Remote Config backend 6. Listen for updates
14. 1. Set up a new Firebase Project
15. 1. Set up a new Firebase Project
16. 1. Set up a new Firebase Project
17. 1. Set up a new Firebase Project
18. 2. Integrate the SDK
19. 2. Integrate the SDK
20. 2. Integrate the SDK
21. 2. Integrate the SDK
22. 2. Integrate SDK dependencies { // Import the BoM for the Firebase platform implementation(platform("com.google.firebase:firebase-bom:32.3.1")) // Add the dependencies for the Remote Config and Analytics libraries implementation("com.google.firebase:firebase-config-ktx") implementation("com.google.firebase:firebase-analytics-ktx") }
23. 2. Integrate the SDK
24. 3. Create a new Feature Flag
25. 3. Create a new Feature Flag
26. 3. Create a new Feature Flag
27. 3. Create a new Feature Flag
28. 4. Initialize Remote Config class FeatureChecker { private val remoteConfig = FirebaseRemoteConfig.getInstance() init { val configSettings = remoteConfigSettings { minimumFetchIntervalInSeconds = 3600L } remoteConfig.setConfigSettingsAsync(configSettings) } }
29. 5. Set Default Values remoteConfig.setDefaultsAsync( mapOf( "detailsScreenEnabled" to false, "descriptionMaxLineCount" to 2L, "detailsNavigation" to "BOTTOM_SHEET" ) )
30. 6. Fetch Remote Values suspend fun fetchFeaturesConfig(): Boolean { return remoteConfig.fetchAndActivate().await() } • Blocking during app startup (splash screen) • Async and update immediately • Async and use new values next time
31. 7. Read Values fun isFeatureEnabled(featureFlagName: String): Boolean { return remoteConfig.getBoolean(featureFlagName) } fun getLongValue(key: String): Long { return remoteConfig.getLong(key) }
32. 6. Read Values class ViewModel(private val featureChecker: FeatureChecker) : ViewModel() { private val _detailsScreenEnabled: MutableStateFlow<Boolean> = MutableStateFlow(false) val detailsScreenEnabled: StateFlow<Boolean> = _detailsScreenEnabled init { viewModelScope.launch { _detailsScreenEnabled.update { featureChecker.isFeatureEnabled("detailsScreenEnabled") } } } }
33. 6. Using it in Compose with a ViewModel val detailScreenEnabled = viewModel.detailsScreenEnabled .collectAsState() .value if (detailsButtonEnabled) { IconButton( onClick = {}, ) { Icon( Icons.Default.ArrowForward, contentDescription = "Open details" ) } }
34. 8. Observe Updates in Real-Time • Receive new values as soon as published • Opens HTTP connection to Remote Config backend Source: https://firebase.google.com/docs/remote-config/real-time?platform=android
35. 8. Observe Updates in Real-Time suspend fun observeFeatureConfigChanges() = callbackFlow { firebaseRemoteConfig.addOnConfigUpdateListener(object : ConfigUpdateListener { override fun onUpdate(configUpdate: ConfigUpdate) { firebaseRemoteConfig.activate().addOnCompleteListener { trySend(configUpdate.updatedKeys) } } override fun onError(error: FirebaseRemoteConfigException) { close(error.cause) } }) awaitClose { } }
36. 8. Observe Updates in Real-Time featureChecker.observeFeatureConfigChanges() .filter { it.contains("detailsScreenEnabled") } .map { featureChecker.isFeatureEnabled("detailsScreenEnabled") } .collectLatest { featureEnabled -> _detailsScreenEnabled.update { featureEnabled } }
37. 7. Observe Updates in Real-Time
38. Conditions
42. Additional Capabilities • A/B experiments ◦ Used with Google Analytics • Personalization ◦ Uses ML to deliver custom experience to each user ◦ Automatically achieve maximum conversion ◦ Can be useful for showing ads, adjusting difficulty level in a game, …
43. Setting up an A/B Experiment • how to set up • how to target specific users • code examples
47. Firebase Remote Config Limitations • Free to use for unlimited daily active users • Maximum 2000 parameters • Parameter keys can be up to 256 characters long • Maximum 500 conditions • Throttling (default is 12 hours) • Up to 300 total A/B experiments (max 24 running)
48. Summary • Feature flags are a powerful tool • Make building and releasing mobile apps both safer and faster • Benefits outweigh the drawbacks • Stick to the best practices • Easy to get started with Firebase Remote Config
49. Thank you! domenlanisnik @DomenLanisnik @domen.lanisnik