Push Notifications Deep Dive: FCM, APNs, OneSignal & Firebase Cloud Messaging

🔔 1. Push Notification Architecture Overview

• Client apps register with platform services (FCM/APNs) and receive device tokens.

• Backend servers send payloads to gateway endpoints, which route messages to devices.

• Topics & segments enable mass delivery without storing individual tokens.

📮 2. Firebase Cloud Messaging (FCM) for Android & iOS

• Data vs Notification payloads: data handled in background, notification auto‑displayed.

• High‑priority vs normal message priority.

• FCM HTTP v1 API with OAuth2 service accounts.

📱 3. Apple Push Notification Service (APNs)

• JWT‑based authentication with 10‑minute Expiration.

• Payload limits: 4 KB.

• Notification service extension for rich media.

🌐 4. OneSignal as Unified Layer

• Cross‑platform SDKs abstracting FCM & APNs.

• Segmentation, A/B testing, and automation.

• Web and email channel orchestration.

📊 5. Comparison Table:

🛠️ 6. Best Practices for Reliable Delivery

• Batch & collapse keys to avoid spamming.

• Use high priority only for time‑sensitive messages.

• Handle token refresh and invalidation (HTTP 410 for APNs).

• Localize content and respect quiet hours.

• Validate payload JSON with linters.

🔗 Reference Links:

• https://firebase.google.com/docs/cloud-messaging

• https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server

• https://documentation.onesignal.com/

🏷️ Hashtags: #pushnotifications #FCM #APNs #OneSignal #firebase #mobiledev #androiddev #iosdev #flutter #notificationengagement