Push Notifications
What are Push Notifications?
Push notifications are messages sent from a server to a user's device or browser, even when the application is not actively in use.
They are a core mechanism for re-engaging users, delivering real-time updates, and triggering return visits.
Push notifications are widely used in social applications, messaging platforms, and community-driven products.
Why push notifications matter
Most users are not constantly active in an app.
Push notifications bridge this gap by bringing users back when something important happens.
- Notify users of new messages
- Alert users to interactions (likes, comments)
- Drive re-engagement and retention
Push notifications are the trigger that brings users back into the product.
Types of push notifications
Push notifications vary based on platform and use case:
- Mobile push: sent to iOS and Android devices
- Web push: sent to browsers
- In-app notifications: displayed while the user is active
Each type has different delivery mechanisms and constraints.
How push notifications work
The push notification flow involves multiple systems:
- User action generates an event
- The event is processed by backend services
- A notification is created and queued
- The message is sent through platform gateways (APNs, FCM)
- The device receives and displays the notification
This process must be reliable and low latency.
Event-driven notification systems
Push notifications are typically built on event-driven architecture.
Examples:
- User receives a message → trigger notification
- User gets a like → trigger notification
- User is mentioned → trigger notification
Each event can trigger one or more notifications.
Real-time vs delayed notifications
Notifications can be delivered in different modes:
Real-time notifications:
- Triggered instantly
- Used for messages and urgent updates
Delayed or batched notifications:
- Grouped and sent periodically
- Used for digests or summaries
Choosing the right approach depends on user experience goals.
Integration with social systems
Push notifications are tightly integrated with core social infrastructure:
- Real-Time Messaging triggers message alerts
- Activity Feed interactions generate notifications
- Social Graph determines relevance
They act as the external layer that surfaces activity to users.
Notification ranking and prioritization
At scale, users can receive large volumes of notifications.
Systems must prioritize and rank notifications based on:
- Relevance
- Recency
- User preferences
This is often integrated with feed ranking systems.
Delivery challenges and reliability
Push notification systems must handle:
- Device-specific delivery constraints
- Network variability
- Rate limits from platform providers
Delivery is not always guaranteed, especially for background notifications.
Scaling notification systems
At scale, notification systems must process millions of events.
Key strategies include:
- Queue-based processing pipelines
- Batching and rate limiting
- Distributed delivery systems
Efficient scaling is critical for performance and cost control.
Common failure modes
- Notification spam leading to user fatigue
- Delayed delivery due to queue backlogs
- Dropped notifications from platform limits
- Poor targeting reducing relevance
These issues can negatively impact user experience.
Best practices for push notifications
- Send only high-value, relevant notifications
- Allow users to control notification preferences
- Use personalization to improve engagement
- Avoid excessive frequency
Well-designed notifications increase engagement without overwhelming users.
Build vs buy: notification infrastructure
Building a push notification system involves integrating multiple services and handling edge cases.
Building in-house
Requires managing queues, delivery pipelines, and platform integrations.
Using a Social SDK
Provides integrated notification systems connected to feeds and messaging.
See also: Social SDK
Why push notifications drive retention
Push notifications directly influence user behavior:
- Increase return frequency
- Re-engage inactive users
- Drive real-time interaction
They are one of the most effective tools for improving retention.
Push notifications are the bridge between user activity and user attention.
FAQs
They can be real-time, but delivery depends on platform constraints and network conditions.
No. Delivery depends on device state, permissions, and platform limitations.
Push notifications are sent to devices outside the app, while in-app notifications appear within the app.
By prioritizing relevance, limiting frequency, and allowing user preferences.