APNS

APNs stands for Apple Push Notification service, a cloud-based delivery system created by Apple to enable third-party apps to deliver short messages to Apple devices. It provides a persistent, bidirectional channel from devices to Apple servers, allowing apps to receive notifications even when not running. On registration, an app on iOS, iPadOS, watchOS, macOS, or tvOS obtains a device token from APNs, which uniquely identifies the app instance on that device. The app’s backend stores this token and uses it to target push notifications to that device. Notifications can be sent via the modern HTTP/2-based APNs provider API or, in older setups, via a certificate- or token-based legacy protocol.

Delivery flow: the app server authenticates with APNs using a provider method (certificate or token with a private key) and sends a payload addressed to the device token. APNs routes the notification to the appropriate device when online; if the device is offline, APNs may queue and deliver later. Payloads can update app icons (badge), play a sound, or deliver content-available messages for background updates. Developers can specify a priority to influence delivery timing.

Security and management: Communications with APNs are over TLS. Provider authentication uses a signed token or certificate; tokens can be rotated. APNs supports separate development (sandbox) and production environments.

Limitations: APNs does not guarantee delivery or ordering, and delivery depends on device state, network conditions, and user settings. APNs remains the primary mechanism for push notifications in the Apple ecosystem, enabling apps to engage users with timely updates.