How to Build an Activity Feed: Architecture and Tradeoffs

Modern activity feeds in applications have evolved from simple reverse-chronological lists to complex systems that enhance user interaction with features like likes, threads, GIFs, replies, and read receipts. Building an efficient activity feed today involves creating a scalable architecture that supports real-time updates and never loses messages, typically facilitated by a combination of an activity store, aggregation logic, and a read state tailored per user. The architecture comprises several layers: an append-only activity store that serves as the source of truth, an aggregator that groups similar activities to reduce redundancy, and a read state that tracks what users have seen. Filtering and feed views allow users to slice the activity stream based on their interests, and real-time updates ensure users are notified promptly of new activities. The UI layer is crucial for user comprehension, requiring thoughtful rendering of activities and aggregates. While some teams may opt to build a custom solution, others might leverage a hosted feeds API like Stream Feeds to handle the infrastructure, allowing them to focus on unique product requirements such as the activity model and user interface.