Centrifugo introduction
Centrifugo is an open-source real-time messaging server. Centrifugo can instantly deliver messages to application online users connected over supported transports – WebSocket, HTTP-streaming, Server-Sent Events (SSE), WebTransport, GRPC. Centrifugo is built around channel concept – clients subscribe to channels to receive publications, different subscriptions are multiplexed over a single connection to the server. So Centrifugo is a user-facing PUB/SUB server, with many additional features around this core concept.
Centrifugo is language-agnostic and can be used to build chat apps, live comments, multiplayer games, real-time data visualizations, collaborative tools, AI streaming responses, etc., in combination with any backend and frontend. It is well suited for modern architectures and allows decoupling of business logic from the real-time transport layer.
Centrifugo provides channel history with automatic stream recovery on reconnect, online presence to see who is currently subscribed to a channel, and delta compression to reduce bandwidth usage.
Centrifugo scales horizontally, allowing multiple Centrifugo nodes in a cluster to load balance client connections. A message published to any Centrifugo node in this setup will be delivered to online subscribers connected to other nodes. This is achieved through an integration with a set of high-performance PUB/SUB brokers capable of handling millions of concurrent channels.
Several official SDKs for browser and mobile development wrap the bidirectional client-to-server protocol, offering a straightforward API for real-time subscriptions multiplexed over a single connection. These SDKs handle reconnects, manage ping-pong, timeouts, and deal with other complexities of working with real-time connections. Additionally, Centrifugo supports a unidirectional approach for simple use cases with no SDK dependency.
By real-time, we refer to a soft real-time system. This means there are no strict latency timing constraints. Centrifugo does its best to minimize delivery delays, but due to factors like network latencies, garbage collection cycles, and so on, those can't be guaranteed.
Background and motivation
Centrifugo was born more than a decade ago to help applications whose server-side code was written in a language or framework lacking built-in concurrency support. In such cases, managing persistent connections can be a real headache, usually resolvable only by altering the technology stack and investing time in developing a production-ready solution.
For instance, frameworks like Django, Flask, Yii, Laravel, Ruby on Rails, and others offer limited or suboptimal support for handling numerous persistent connections for real-time messaging tasks.
Here, Centrifugo provides a straightforward and non-obtrusive way to introduce real-time updates and manage many persistent connections without radical changes in the application backend architecture. Developers can continue to work on the application's backend using their preferred language or framework, and keep the existing architecture. Just let Centrifugo deal with persistent connections and be the real-time messaging transport layer.
These days, Centrifugo offers advanced and unique features that can significantly simplify a developer's workload and save months (if not years) of development time, even if the application's backend is built with an asynchronous concurrent language or framework. The documentation uncovers features step by step.
Centrifugo fits well with modern architectures and can serve as a universal real-time component, regardless of the application's technology stack. It stands as a powerful self-hosted alternative to cloud solutions like Pusher, Ably, or PubNub. Moreover, due to its self-hosted nature, Centrifugo may offer deeper integration of real-time connection management with your application backend.
Beyond PUB/SUB
While Centrifugo started as a PUB/SUB server for delivering messages to channels, it has evolved beyond that. Features like map subscriptions and shared poll subscriptions introduce real-time state synchronization — where Centrifugo manages not just message delivery, but the state itself.
With map subscriptions, channels maintain a live key-value state that is automatically synchronized to all subscribers. Clients receive the current state on subscribe, catch up efficiently on reconnect, and get incremental updates in real-time. Coupled with PostgreSQL integration, your application can publish state changes transactionally — within the same database transaction as your business logic — eliminating the dual-write problem entirely. For applications that already own state in their own database and want Centrifugo to only deliver change events, the PostgreSQL stream broker paired with the getState callback on stream subscriptions covers that pattern.
This shifts Centrifugo from a transport layer into a real-time data synchronization platform — applications can rely on Centrifugo not just to push events, but to keep distributed clients in sync with shared, mutable state.