Notification Feeds

Whether it's new matches in a dating app or student responses in a learning management system, users rely on notification feeds to track relevant activity.

What Are Notification Feeds?

A notification feed is a dedicated, persistent stream within an application designed to display all personalized updates, alerts, and other user-relevant activities. These feeds give developers full end-to-end control for relaying information to users.

For example, social media platforms like Instagram often have notification feeds so users can keep track of likes, comments, DMs, and more. They are often used alongside content-focused feeds, such as activity feeds that distribute user-generated content.

How Do Notification Feeds Work?

Let's take a look at the underlying steps in the notification feed pipeline.

Event Generation and Ingestion

They start with events that trigger the rest of the pipeline. These events are captured by the backend infrastructure and subsequently pushed into the notification system.

Triggering events usually fall under user actions (such as likes, follows, or comments) or system updates (like payment processing or a shipment arriving).

Large-scale systems heavily rely on message queuing or streaming platforms, such as Kafka and RabbitMQ, to manage massive volumes of incoming events. These systems keep ingestion reliable, guaranteeing that no information is lost when properly configured.

Feed Construction and Data Modeling

After events are ingested, the system stores the individual notifications. These become the building blocks to construct feeds for each user based on relevance or chronological order.

To keep everything searchable and logged, notifications are enriched with metadata like user IDs, content references, and priority levels. This metadata allows advanced filtering and grouping.

Optimized databases and caching layers, such as Redis and Memcached, make it possible for feeds to update and quickly display their contents. This architectural choice increases read/write throughput. 

Personalization and Relevance

After feeds are constructed, product and engineering teams fine-tune them to improve the user experience.

Most feeds aggregate notifications to combat user fatigue. This involves grouping similar alerts together. For example, a notification feed can include a single entry like, "20+ people liked your post" rather than separate notifications for every individual like.

Developers also employ techniques to prioritize information within the feed based on user relevance. For example, a system might assign higher priority to a chat message than a promotional notification, placing it first in the feed.

Scalability and Reliability

Effective notification systems are built to handle increases in user activity and consistently deliver updates with low latency. This is achieved in part through an architectural pattern known as fan-out that sends the notifications to multiple endpoints from a single source.

Notification feeds often use one or a combination of two fan-out models:

• Fan-out on write (push-based): Notifications are immediately written to the individual feeds of all relevant users at the moment of creation. This offers fast-read performance, but it's costly and complex to manage as volume increases.

• Fan-out on read (pull-based): Notifications are dynamically retrieved, aggregated, and constructed when the user opens their feed. This provides greater flexibility and is simpler on the write side, but can lead to slower read times.

Regardless of the model, maintaining performance also relies on strategies like caching, database sharding, and robust distributed queues. Additionally, fault tolerance mechanisms are put into place throughout the system to reliably prevent any message or lost event.

Notification Feed Use Cases

This type of feed is used in many different types of applications, including:

Social Media and Chat Messaging Apps

Notification feeds supply updates on user-to-user interaction.

These feeds immediately validate and reward user behavior, creating a powerful engagement loop.

Alerts cover: 

• Direct interactions, such as likes, reactions, comments, replies, livestreams, and mentions

• Network growth and performance notifications about new followers, accepted friend requests, post impressions, and more

This system is designed to keep users active in their social graph and encourage them to return to post or interact in other ways, as seen on platforms (like Instagram, X, and Facebook) and chat apps (like Discord and Messenger).

Productivity and Workflow Management

For enterprise, project management, and developer tools, these feeds become part of the workflow management process. They keep team members aligned on progress and pending tasks.

Feed items can be: 

• Alerts for assignments, such as when a user is directly tasked with an issue or ticket

• Collaboration updates, like when a team member replies to a thread or uploads a file

• Status changes for pull requests, task completion, and more

On platforms like Slack, Trello, and GitHub, the goal is to reduce the in-app inbox clutter by centralizing action items and ensuring rapid responses to important updates.

eCommerce and Service Updates

Notification feeds become a channel for customer service, promotion, and transactional transparency in eCommerce and service applications. They provide timely, non-intrusive status updates that build customer confidence in the app.

Examples include: 

• Transactional status alerts confirming order placements, shipment tracking updates, and delivery confirmations

• Financial and account security, such as messages regarding large transactions or new device logins

• Personalized promotions like price drops on saved items

This use case is widely applicable across:

• Marketplace apps, like SheIn and Amazon

• Personal banking and other fintech apps

• Ride share and delivery service apps, including Uber and DoorDash

Best Practices for Implementation 

Consider implementing the following best practices when building or updating your feeds:

Rank by Relevance

Ranking by individualized relevance provides the most valuable information to each user first.

Sender affinity (relationship strength) and past user behavior are just some of the factors you can use to implement a personalized ranking function.

For instance, if a social app user ignores most activity feed notifications but almost always clicks on livestream announcements from a specific account, your feed can place those announcements at the top of the feed.

Keep Notifications Concise and Actionable

Notification content should be:

• Concise: Users will ignore overly long messages, so adhere to strict character limits. You should also create standardized, localized templates for different languages.

• Actionable: Give users something to do with each item, like "You have five new followers. Click here to view them." or "Tap to try our new selfie filters."

Moderate Proactively

Without moderation, harmful content like harassment, spam, or illegal activity can creep into your feeds. You can increase user trust and protect yourself from potential legal issues by accounting for this in your moderation policy.

One method is to use an automated filtering system that discards events based on policy standards. You can get users involved by implementing a report feature that escalates to human moderators if any violations sneak through.

Measure and Iterate Continuously 

Your feed's first version won't be perfect and should be revisited regularly.

You can track user engagement metrics (like taps by notification or activity type) or performance stats (such as load time) to gauge what works and what needs improvement.

Use A/B testing to validate changes to ranking algorithms, aggregation logic, and other feed components.

Secure and Optimize the Pipeline

Your feeds can break in two ways: 

• Malicious attacks: Denial of service, injection attempts, and other exploits can bring down your feed or harm users. Follow secure coding practices like input validation and output encoding to minimize the chances of this happening.

• Capacity overload: Unexpected surges in legitimate traffic or system-generated events can also lead to downtime. Select the appropriate fan-out strategy based on an assessment of latency requirements and anticipated event volume. You should also implement rate limiting.

Frequently Asked Questions