Action Cable

Action Cable is a WebSocket framework built into Rails that enables real-time server→client communication.

Server (Channel): Subscribe to channels in ChatChannel with stream_from "chat_room_1" in the subscribed method, and broadcast received data with ActionCable.server.broadcast.

Client (JavaScript): Subscribe to channels with consumer.subscriptions.create, and reflect received data in the DOM via the received callback.

Combined with Turbo Stream, real-time DOM updates are possible without JavaScript. Use Turbo::StreamsChannel.broadcast_append_to to add/modify/delete DOM elements directly from the server.

WebSocket Use Case: Real-time Speech-to-Text (STT)

WebSocket is key for real-time speech recognition (STT). Services like Deepgram and Azure Speech open a WebSocket connection and stream audio in 100-200ms chunks, returning interim and final results in real-time.

REST API approach (Groq Whisper): Cut recordings into 4-second segments sent via HTTP POST → 4-5 second delay, context loss
WebSocket approach (Deepgram/Azure): Continuous audio chunk streaming → 0.3-1 second delay, context preserved

Notes for WebSocket in Rails

1. Production adapter required

• Development: async adapter (default, single process)

• Production: must use redis or solid_cable adapter

• Rails 8: Solid Cable (DB-based) available — production without Redis

2. Nginx/Reverse proxy configuration

• WebSocket requires HTTP Upgrade handshake — separate Nginx config required

3. Authentication & Security

• Authenticate in ApplicationCable::Connection with cookies.encrypted[:user_id]

• config.action_cable.allowed_request_origins — required domain allowlist

• Production: must use wss:// (TLS)

4. Connection management & memory

• Each WebSocket connection occupies server memory persistently

• Clean up resources in Channel unsubscribed callback

5. Horizontal scaling

• Multi-server: Redis Pub/Sub for cross-server message sync

• Load balancer: Sticky Session required

• Large scale: Consider AnyCable — Go/Rust based, 10x performance vs Ruby, Action Cable API compatible

6. Testing

• ActionCable::Channel::TestCase for Channel unit tests

• assert_broadcast_on / assert_has_stream for broadcast verification

• Integration tests: Capybara + JS driver (System Test) for WebSocket behavior