Building a Realtime Websocket API in Phoenix
summary
Built a realtime WebSocket API with Phoenix and Elixir where the server is the authoritative timer and each user gets an OTP process as the timer, tracked and rehydrated on restart, using a GraphQL connect mutation that returns a token and WS URL, custom JSON messages shaped as [model, action] with timestamped tick events every second, tests verifying the OTP timer state and throughput with Blaze, removed Phoenix channel internals to simplify clients, heartbeat and reconnect logic handle intermittent drops and the cross‑device sync works.
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chapters (25)
- 0:00Introduction
- 1:05Talk overview
- 3:54Websockets for Pomodoro
- 6:08What is websocket
- 10:26Websockets vs HTTP
- 11:28Phoenix and Elixir
- 13:13OTP and hot code reload
- 14:20Realtime API inspiration
- 15:03GraphQL API setup
- 20:51Phoenix websocket OTP
- 21:34Phoenix channels
- 25:26Custom websocket API
- 26:08Message structure
- 27:13Timer start events
- 30:01Broadcasting events
- 32:53Implementation flow
- 33:59Q&A Elixir ecosystem
- 36:32Q&A language servers
- 36:53Q&A resilience
- 38:38Q&A message ordering
- 39:53Q&A client support
- 40:55Q&A message frequency
- 42:25Q&A reconnecting heartbeats
- 44:08Q&A timing precision
- 44:52Q&A multi-server sync
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