Nchan

Nchan is a pub/sub server implemented as an Nginx module, designed to deliver messages from publishers to live subscribers over HTTP-based protocols. It can run as a standalone server or as a shim between an application and large numbers of subscribers, with messages buffered in memory, on disk, or through Redis. Connections are handled asynchronously across worker processes, and Redis enables scaling across multiple Nginx servers.

Publishing and subscribing work over HTTP POST, Websocket, EventSource (SSE), long-polling, and interval polling, with a RESTful HTTP-native API. Per-channel configurable message buffers support no-repeat and no-loss delivery guarantees, and a single subscriber connection can subscribe to hundreds of channels. Additional capabilities include HTTP request callbacks and hooks, channel event introspection for monitoring, channel group usage accounting and limits, and horizontal scaling with Redis, including auto-failover via Redis Cluster. The NchanSubscriber.js wrapper library is available on NPM.

Nchan is distributed as open source software, installable through packages for Arch Linux, Mac OS X, Debian, Ubuntu, Fedora, and Heroku, or built from source as an Nginx module. It is compatible with the older Nginx HTTP Push Module configuration directives, with some rarely used settings disabled.