Nchan Expert

Overview

This skill provides procedural knowledge for configuring, optimizing, and securing Nchan, the high-performance pub/sub module for Nginx.

Core Capabilities

1. Endpoint Configuration

Nchan maps Nginx locations to pub/sub endpoints.

• Publishers: Use nchan_publisher to create endpoints that accept messages via HTTP POST or Websockets.
• Subscribers: Use nchan_subscriber to support Websocket, EventSource (SSE), Long-Polling, and more.
• PubSub: Use nchan_pubsub for locations that act as both.

2. Scalability & Storage

Nchan supports local memory storage and Redis for horizontal scaling.

• Redis Modes: Distributed (shared), Backup (persistence), and Nostore (broadcast).
• Redis Cluster: High availability and sharding support.
• See references/storage.md for details.

3. Security & Access Control

Secure your channels using various patterns:

• Authorization: nchan_authorize_request for delegating auth to an upstream application.
• Internal Redirects: X-Accel-Redirect for hiding channel IDs.
• ACLs: Standard Nginx allow/deny for publisher endpoints.
• See references/security.md for implementation patterns.

4. Advanced Messaging Features

• Multiplexing: Subscribe to up to 255 channels over one connection.
• Channel Groups: Use nchan_channel_group for accounting and namespace isolation.
• Upstream Hooks: nchan_publisher_upstream_request for mutating messages before they are published.

5. Monitoring & Introspection

• Stub Status: nchan_stub_status for real-time metrics.
• Channel Events: nchan_channel_events_channel_id for debugging channel lifecycle events.
• Variables: Use Nchan-specific variables like $nchan_channel_id and $nchan_subscriber_count.
• See references/variables.md for a full list.

Resources

• references/directives.md: Comprehensive list of configuration directives.
• references/variables.md: Nchan-specific Nginx variables.
• references/security.md: Security and authorization patterns.
• references/storage.md: Memory and Redis storage configuration.
• references/testing.md: Minimal testing patterns with curl (stats, pub/sub, wss).