Push notifications in apps: Architecture, APNs & FCM explained

Push notifications have long been an integral part of modern app architectures. They make it possible to reach users specifically and in real time — whether for reactivation, for relevant system information or to trigger individual events. Used correctly, push messages not only improve user loyalty, but also the efficiency of app communication. But behind the seemingly simple function lies a complex technical system.

In this article, we look at push notifications from a developer perspective: from architecture to integration to best practices for iOS, Android, and cross-platform apps.

How do push notifications work technically?

Push notifications are based on an event-driven model. Instead of the app regularly asking the server for new data (polling), the device actively receives a message from the system as soon as an event requires it. This mechanism reduces energy consumption and ensures greater efficiency in communication between server and device.

The basic architecture is as follows:

1. The app registers with the respective operating system (iOS or Android) for push notifications.
2. The system issues a device token that uniquely identifies the device.
3. The app sends this token to its own backend.
4. As soon as a message is to be sent, the backend transfers the message text and token to the push service (e.g. FCM or APNs).
5. The push service takes over delivery to the respective device.

Push messages can be visible (notification), but can also be processed invisibly in the background (silent push), for example to synchronize data or prepare updates.

Comparing push systems: Android vs. iPhone

iPhone push notifications (APNs)

The push notification on the iPhone is handled via the Apple Push Notification Service (APNs). This uses a token-based system, in which each device receives a unique token that is used for delivery. In contrast to Android, iOS requires an explicit opt-in — no push message may be received without the user's active consent.

Communication with APNs is carried out using an encrypted HTTP/2 protocol. Developers must configure an appropriate certificate or JWT to send messages. The maximum payload size is 4 KB. In addition to classic notifications, Apple also allows so-called “silent pushes”, which do not display a notification but trigger background processes — for example to update data.

Push notifications on the iPhone are subject to strict system policies. If the function is misused — for example due to too many or irrelevant messages — many users deactivate it directly in the system settings. Developers should therefore not only implement in a technically clean manner, but also pay attention to clear added value.

Push messages on Android devices (FCM)

Push messages on Android run on Firebase Cloud Messaging (FCM), Google's official messaging service. Integration is relatively uncomplicated: The Firebase SDK handles token management, delivery and, optionally, topic messaging.

A big difference to iOS: Android does not require an explicit opt-in for push notifications — at least technically. However, from a UX perspective, it is advisable to transparently inform users what pushes are used for. Android allows fine-grained control over which types of messages are sent and how they are displayed via notification channels.

Android is often more reliable when it comes to delivery, especially in the background. However, restrictions may occur as a result of aggressive energy optimization by individual manufacturers. In such cases, manual whitelisting of the app or targeted workarounds at code level is worthwhile.

Client-side integration: Tokens, States & UX

Client-side integration starts with a permission prompt. This is optional for Android, but mandatory for iOS. Developers should choose the ideal time to query — not directly at app launch, but context-based, for example after onboarding or with a feature that clearly explains why pushes are helpful.

After approval has been given, the device token is generated and must be securely transferred to the app backend. This is usually done via a secure HTTPS connection and is linked to the user account there.

The decisive factor is how the app reacts to notifications:

• In the foreground: Push is often not automatically displayed — developers must adapt the UI themselves.
• In the background: The operating system automatically displays the notification.
• When the app is closed: The system service takes over completely.

Android also requires the definition of notification channels, iOS uses notification categories. Both help to implement user preferences in a technically correct way.

Backend architecture: delivery, error handling & segmentation

A stable push system requires a robust backend. The following aspects should be considered:

Token management

Device tokens have a limited validity period and are subject to change. If there are error codes such as invalidRegistration or NotRegistered, tokens should be removed from the database. Automated routines help clean up outdated tokens regularly.

Retry mechanisms

Deliveries can fail — for example, if the network connection is poor or notifications are disabled. A retry system with exponential backoff avoids unnecessary server load and increases the success rate.

Segmentation & Targeting

Pushes should never be sent “to everyone.” Instead: segment users, personalize content, incorporate context. This significantly increases relevance and interaction rate.

Such a setup is particularly important in the Cross platform app developmentbecause it ensures consistent results across multiple platforms.

Activate privacy & push notification: What developers need to know

Even though the topic is often pushed back to the product team, developers share responsibility when it comes to data protection and user control. With iOS, push notifications can only be activated with consent. Android technically allows more — but the GDPR also applies here.

That's why:

• Clean document push opt-in (consent management)
• Don't transfer sensitive data in the payload
• When deactivated: delete tokens on the server side
• No secret “silent tracking pushes”

The technical focus must be coordinated with ethical handling and legal compliance.

Best practices for developers

Efficient push communication is not the result of technology alone. Successful systems consider:

• Event-based triggers instead of static schedules
• throttling to avoid spam effects
• fallbacks Like in-app messages in case of lack of permission
• Monitoring about opening rates, delivery time and errors
• A/B testingto optimize content, timing, and frequency

For a well-thought-out architecture that combines technology and user experience, a specialized App development agency strategic and technical support.

Conclusion: Push messages as the key to user loyalty

Push notifications are much more than just an additional feature — they're a powerful element of any app strategy. Those who implement them in a technically clean manner, integrate them into an intelligent backend and use them context-sensitively can sustainably improve retention, conversion and engagement.

Developers should not dismiss push as a “marketing thing,” but as an architectural element with direct influence on UX and product impact.

FAQ — Technically speaking