How to fix UNAVAILABLE: The service is currently unavailable in Firebase

// Node.js / JavaScript example
async function firestoreQueryWithRetry(query, maxRetries = 3) {
  for (let attempt = 1; attempt <= maxRetries; attempt++) {
    try {
      return await query();
    } catch (error) {
      if (error.code === 'unavailable' && attempt < maxRetries) {
        // Exponential backoff: 1s, 2s, 4s, etc.
        const delayMs = Math.pow(2, attempt - 1) * 1000;
        console.log(`Retrying in ${delayMs}ms (attempt ${attempt}/${maxRetries})`);
        await new Promise(resolve => setTimeout(resolve, delayMs));
      } else {
        throw error; // Max retries or different error
      }
    }
  }
}

// Usage
const result = await firestoreQueryWithRetry(() =>
  db.collection('users').doc('userId').get()
);

// Flutter / Dart example
Future<T> retryWithBackoff<T>(Future<T> Function() operation, {int maxRetries = 3}) async {
  for (int attempt = 1; attempt <= maxRetries; attempt++) {
    try {
      return await operation();
    } catch (e) {
      if (e is FirebaseException && e.code == 'unavailable' && attempt < maxRetries) {
        final delayMs = (pow(2, attempt - 1) * 1000).toInt();
        print('Retrying in ${delayMs}ms (attempt $attempt/$maxRetries)');
        await Future.delayed(Duration(milliseconds: delayMs));
      } else {
        rethrow;
      }
    }
  }
}

// Usage
final doc = await retryWithBackoff(() =>
  FirebaseFirestore.instance.collection('users').doc('userId').get()
);

// Android / Kotlin example
suspend fun <T> firestoreQueryWithRetry(
  maxRetries: Int = 3,
  query: suspend () -> T
): T {
  repeat(maxRetries) { attempt ->
    try {
      return query()
    } catch (e: FirebaseFirestoreException) {
      if (e.code == FirebaseFirestoreException.Code.UNAVAILABLE && attempt < maxRetries - 1) {
        val delayMs = (2.0.pow(attempt.toDouble()) * 1000).toLong()
        Log.d("Firestore", "Retrying in ${delayMs}ms (attempt ${attempt + 1}/$maxRetries)")
        delay(delayMs)
      } else {
        throw e
      }
    }
  }
  throw IllegalStateException("Retry loop failed")
}

// Usage
val doc = firestoreQueryWithRetry {
  FirebaseFirestore.getInstance()
    .collection("users")
    .document("userId")
    .get()
    .await()
}

// Check if browser is online
if (!navigator.onLine) {
  console.error('Device is offline');
  // Show user an offline message
}

// Listen for connection changes
window.addEventListener('online', () => {
  console.log('Connection restored, retrying...');
  // Retry your operation
});

window.addEventListener('offline', () => {
  console.log('Connection lost');
});

# Verify network connectivity
ping google.com

# Check DNS resolution
nslookup firebaseio.com

# Verify no proxies/firewalls blocking Firebase
curl -v https://firestore.googleapis.com/

# Remove or check the emulator host variable
echo $FIRESTORE_EMULATOR_HOST

# If set, verify the emulator is actually running on that host:port
# Default is usually localhost:8080
nc -zv localhost 8080

# If emulator is NOT running, either start it:
firebase emulators:start

# Or unset the environment variable for production:
unset FIRESTORE_EMULATOR_HOST

// Check environment
if (process.env.FIRESTORE_EMULATOR_HOST) {
  console.warn('Using Firestore emulator at', process.env.FIRESTORE_EMULATOR_HOST);
  // Only should be true in development/testing
}

# Check the detailed deployment logs
firebase deploy --only functions --debug

# Deploy to a specific region if having issues
firebase deploy --only functions --region us-central1

# If deployment keeps failing, try again after a few minutes
# or check the Cloud Service Health dashboard

# JavaScript/Node.js - update Firebase SDK
npm install --save firebase@latest
npm install --save firebase-admin@latest

# Flutter - update cloud_firestore
flutter pub upgrade cloud_firestore

# Android - update via Gradle or Android Studio dependency management
# Check build.gradle for com.google.firebase:firebase-firestore version

# iOS - update via CocoaPods
pod update Firebase

npm list grpc @grpc/grpc-js

# Modern versions should use @grpc/grpc-js (not the older 'grpc' package)
# Update if needed:
npm install --save @grpc/grpc-js