Offline-First Mobile Architecture: Building Apps That Work Without Internet

Why Offline-First?

Mobile users expect apps to work everywhere: underground, in rural areas, on flights. Offline-first architecture ensures your app degrades gracefully when connectivity is lost.

Architecture Components

1. Local Database

We use Realm for local storage because of its reactive queries and conflict resolution support.

const realm = await Realm.open({ schema: [TaskSchema, UserSchema] });

// Write locally. Instant, no network required
realm.write(() => {
  realm.create("Task", { id: uuid(), title: "New Task", synced: false });
});

// Read locally. Instant, no loading states
const tasks = realm.objects("Task").filtered("synced == false");

2. Sync Engine

A background sync engine pushes local changes to the server and pulls remote changes when connectivity returns.

class SyncEngine {
  async syncPendingChanges() {
    const pending = await this.localDb.getUnsynced();
    for (const item of pending) {
      try {
        await this.api.push(item);
        await this.localDb.markSynced(item.id);
      } catch (error) {
        this.queueForRetry(item);
      }
    }
  }
}

3. Conflict Resolution

Testing Offline Behavior

• Airplane mode testing on real devices
• Network throttling simulation
• Sync conflict scenario testing
• Data integrity verification after sync