Remote Config: dynamic parameters for mobile apps without resubmission

You have a critical bug in your app: authorization is broken on iOS 17.2. The fix is ready in code, but the build goes through review for 2 days, and App Store takes another day. Dynamic Config disables the problematic feature in 10 minutes without a release. We've implemented it in 20+ projects with up to 10 million users: from fintech to marketplaces. In practice, a config service cuts reaction time for urgent changes from 3 days to 10 minutes — 432 times faster. Savings on hotfixes reach 90%, and release cycle costs are reduced by 30%. For example, in a project with 5 million users, proper configuration saved significant emergency fix expenses.

Remote Config delivers configuration parameters to a mobile app without updates via App Store or Google Play. Unlike Feature Toggles, which control turning features on/off, dynamic configuration handles numeric, string, and JSON parameters. For instance, a Feature Toggle enables a new feed algorithm, while Remote Config sets the number of posts (5, 10, 15) and text length. Our experience ensures you avoid typical pitfalls: exceeding the Firebase quota (10,000 fetches/day), incorrect defaults, or leaking sensitive data.

Remote Config: dynamic mobile app parameters — why and how?

Remote Config lets you change parameters without a release, critical for A/B tests, hotfixes, and adapting to different markets. Unlike Feature Toggles, it works with any data type: numbers, strings, JSON. This gives flexibility: you can change API limits, server URLs, texts, colors, and even entire UI blocks.

How to set up Firebase Remote Config?

Step 1. Integrate the SDK — dynamic remote config

iOS:

let remoteConfig = RemoteConfig.remoteConfig()
let settings = RemoteConfigSettings()
settings.minimumFetchInterval = isDebug ? 0 : 3600
remoteConfig.configSettings = settings

Android (Kotlin):

val remoteConfig = Firebase.remoteConfig
remoteConfig.setDefaultsAsync(R.xml.remote_config_defaults)

Firebase documentation recommends a minimum fetch interval of 3600 seconds for production builds.

Step 2. Set default values

This is not optional. If Remote Config is unavailable (first launch without a network, Firebase outage), the app works with defaults. Without explicitly defined defaults, the SDK returns empty strings and zeros. api_timeout_seconds = 0 — every request immediately times out. Defaults on iOS are in RemoteConfigDefaults.plist, on Android in res/xml/remote_config_defaults.xml. When adding a new parameter, the default is added simultaneously.

Step 3. Fetch + Activate

remoteConfig.fetchAndActivate { status, error in
    let timeout = remoteConfig["api_timeout_seconds"].numberValue.intValue
}

remoteConfig.fetchAndActivate().addOnCompleteListener { task ->
    val maxRetries = remoteConfig.getLong("max_auth_retries").toInt()
}

How to avoid typical Remote Config mistakes?

Defaults are a safety net in case of network failure or server error. Store them in the repository and update them with the code. In one project, the client forgot to set a default for api_timeout_seconds — after the update all requests timed out. We fixed it in an hour, but lost 15% of active users. 100% of projects with Remote Config must have defaults for every parameter. Another common mistake is exceeding the Firebase quota: the free tier is 10,000 fetches per day. Increase the fetch interval to 12 hours in production, use caching (UserDefaults/SharedPreferences). For A/B tests, consider a custom server or a paid plan. Proper configuration saves up to 100,000 fetches per month (10% of the free plan quota).

Remote Config readiness checklist:

• All parameters have defaults
• Fetch interval set: production ≥ 3600 sec, debug = 0
• Client-side caching implemented
• Targeting conditions correct (version, country, percentage)
• Load testing performed (simulate offline)
• Documentation for adding new parameters

Conditions

Remote Config supports targeting by: app version, country/region, device language, random user percentage. This allows:

• Enable a new CDN endpoint only for European users
• Show a special configuration for beta testers (app version contains "beta")
• Gradually roll out a new feed algorithm to 10% of users

Comparison: Firebase Remote Config vs custom config service

Remote Config vs Feature Toggles: what's the difference?

In practice, they are combined: Feature Toggles enable a new module, Remote Config sets its configuration.

When is a custom Remote Config service needed?

Firebase isn't always suitable: you can't send user data to Google, you need custom targeting conditions, or require integration with a corporate IAM system. A minimal architecture includes an API endpoint GET /api/config?appVersion=X&platform=ios&region=eu, Redis for caching, PostgreSQL for storing parameters, and a webhook for instant invalidation. An admin UI lets non-technical staff change values. Contact us for an assessment — we'll select the optimal solution for your infrastructure.

What is included in Remote Config integration work

• Audit of current parameters and strategy selection (Firebase / custom)
• SDK setup, defaults, targeting conditions
• API development (if custom) and admin panel
• Deployment, monitoring, team training
• Documentation for adding new parameters
• 3‑month warranty on correct configuration operation

Get an individual Remote Config implementation plan tailored to your app. Request a consultation — we'll analyze your current configuration and suggest the best solution. Leave a request — we'll contact you within 24 hours to discuss details.

Mobile App Architecture

The app is built in a single ViewController with 2000 lines. Network calls, business logic, UI updates—all in one place. Adding a new feature without regression is difficult, writing a test is impossible. This isn’t “bad code”—it’s a lack of architecture. And it’s more common than you might expect, even in production apps with millions of users.

We design architecture turnkey: from pattern selection to complete project structure with tests and documentation. In 7–10 days you get clean, modular code ready for scaling.

Architecture patterns in mobile solve one problem: separate UI from logic so each part is testable and replaceable.

MVVM: Basic Pattern

Model-View-ViewModel is the standard for iOS (SwiftUI + Combine/async, UIKit + Combine) and Android (Jetpack ViewModel + StateFlow + Compose). The ViewModel holds UI state and business logic. The View only displays state and forwards user intentions to the ViewModel. The Model represents data and its source.

Key rule: ViewModel knows nothing about UIKit or Android View classes. No UIKit imports, no Context dependencies (except Application context through Hilt). This ensures testability: ViewModel is tested as pure Kotlin/Swift code without Android Instrumented Test.

MVVM covers 70% of needs. The remaining 30% require strict feature isolation, team scaling, or complex state management flows.

Clean Architecture: When MVVM Isn’t Enough

Adds layers on top of MVVM:

• Domain layer — business logic, platform-independent. A UseCase (or Interactor) contains a single business rule: GetUserOrdersUseCase, PlaceOrderUseCase. Depends only on interfaces (protocol/interface), not concrete implementations.
• Data layer — repository implementations. OrderRepositoryImpl implements OrderRepository from domain. Knows about Retrofit, Room, UserDefaults. The ViewModel doesn’t know where data comes from—network or cache.
• Presentation layer — ViewModel + View. Knows about Domain, not Data.

Dependency rule: dependencies point inward only. Domain depends on nothing. Data and Presentation depend on Domain.

Presentation → Domain ← Data

This allows swapping implementations: tests use an in-memory repository instead of network, the interface remains the same.

Practical caveat: Clean Architecture adds files and layers. For small apps, this is overhead. It’s justified starting from ~15 features and teams of 3+ developers.

BLoC for Flutter: Predictable State Flow

BLoC (Business Logic Component) is the standard pattern in the Flutter community. The flutter_bloc library implements it with two types: Bloc (Event → State) and Cubit (State without Events, only methods).

Bloc processes Event and emits a new State via on<EventType> handlers. State is immutable—a new object for each change. BlocBuilder re-renders only the part of the tree where state changed.

// Event
abstract class CartEvent {}
class AddItemToCart extends CartEvent {
  final String productId;
  AddItemToCart(this.productId);
}

// State
abstract class CartState {}
class CartLoaded extends CartState {
  final List<CartItem> items;
  CartLoaded(this.items);
}

// Bloc
class CartBloc extends Bloc<CartEvent, CartState> {
  CartBloc(this._cartRepository) : super(CartLoaded([])) {
    on<AddItemToCart>(_onAddItem);
  }

  Future<void> _onAddItem(AddItemToCart event, Emitter<CartState> emit) async {
    final current = state as CartLoaded;
    final updated = await _cartRepository.addItem(event.productId);
    emit(CartLoaded(updated));
  }
}

The advantage of BLoC is testability. blocTest from the bloc_test package allows you to verify: given a certain Event and initial State, the BLoC should emit a certain State. No UI, no mocks for the Flutter framework.

VIPER: For Large iOS Projects

VIPER (View, Interactor, Presenter, Entity, Router) is the strictest separation of responsibilities for iOS. Each component has a protocol and concrete implementation.

• View — UI only, delegates everything to Presenter
• Interactor — business logic, network and data operations
• Presenter — mediator between View and Interactor, formats data for View
• Entity — data models (pure structures)
• Router — navigation between modules

Each module (screen or feature) is a separate VIPER module. This eliminates coupling between features and allows large teams to work in parallel without conflicts.

The cost: many files, many protocols. Boilerplate is generated via Sourcery or custom Xcode templates. VIPER is justified for apps with 10+ developers and 50+ screens.

TCA (The Composable Architecture)

TCA by Point-Free is a more modern alternative to VIPER for iOS/macOS. Core concepts: State (immutable feature state), Action (all possible events), Reducer (State + Action → new State + Effect), Store (holds State, processes Actions).

Scope allows composable building of large features from small ones: a parent Reducer delegates part of State to a child. Each feature is tested in isolation via TestStore with precise control over Effects.

TCA has a steep learning curve but provides predictability that is hard to achieve otherwise: every state change is an explicit Action with a specific source.

Which Pattern to Choose for Your Project?

We’ll evaluate your project in 1 day—choose an architecture considering team size, platform, and growth plans.

There is no universal answer. Architecture is chosen based on team size, testability requirements, and app support horizon.

What Components Are Included in Our Architecture Work?

• Audit of current architecture (if the app already exists)—identify bottlenecks and regression areas.
• Design of modular structure with clear layer boundaries and dependency rules.
• Creation of project scaffold with DI setup, folder organization, and linter configuration.
• Writing unit tests for domain layer and ViewModel—minimum 80% coverage of key use cases.
• Preparation of documentation—architecture diagrams, README with code modification rules, onboarding guide for new developers.
• Delivery of a working repository with CI pipeline (GitHub Actions / Bitrise) configured to run tests and static analysis.

All this is included in the design cost. Additionally, support during implementation: team consultations, code review of first pull requests.

How Does Lack of Architecture Affect Development Speed?

Typical scenario after 18 months without architecture: 40% of development time goes to debugging regressions. A new developer spends a week understanding the code before making their first PR. Tests aren’t written “because it’s hard to mock.” Adding a new feature requires understanding half the codebase.

Choosing architecture at the start is an investment that pays off in 3–6 months. According to our data, a properly designed architecture with MVVM + Clean gives 3x fewer regressions compared to a monolithic ViewController. And the cost of implementation is recouped in 2–3 sprints.

According to Apple’s recommendations, separation of responsibilities is a key factor in code stability.

Why Trust Our Team with Architecture?

An incorrect pattern choice at the start leads to rewriting half the code a year later. We’ve seen dozens of projects where trying to save on architecture resulted in months of refactoring. With over 10 years of commercial development experience and work on apps from 1 to 50 developers, we help avoid common mistakes:

• Overengineering for a simple MVP (we assign MVVM, not VIPER).
• Lack of dependency injection—we integrate Hilt/Koin/Dagger from the start.
• Ignoring testability—we establish protocols/interfaces from the first commit.

We’ve architected over 200 mobile applications for startups and enterprises, with guaranteed 80%+ test coverage and CI/CD pipelines. Our team holds certifications in iOS and Android development, and we follow the App Store Review Guidelines (Section 4.2/5.1) to ensure smooth store approvals.

Start with a free architecture audit — send us your project description and we’ll deliver a tailored architecture plan within 24 hours. Reach out via Telegram or email to get started.