- name
- WebSocket
- description
- Implement reliable WebSocket connections with proper reconnection, heartbeats, and scaling.
- metadata
- {"clawdbot":{"emoji":"🔌","os":["linux","darwin","win32"]}}
Reconnection (Always Forget)
- Connections drop silently—TCP FIN may never arrive; don't assume
onclose fires - Exponential backoff: 1s, 2s, 4s, 8s... cap at 30s—prevents thundering herd on server recovery
- Add jitter:
delay * (0.5 + Math.random())—prevents synchronized reconnection storms - Track reconnection state—queue messages during reconnect, replay after
- Max retry limit then surface error to user—don't retry forever silently
Heartbeats (Critical)
- Ping/pong frames at protocol level—browser doesn't expose; use application-level ping
- Send ping every 30s, expect pong within 10s—no pong = connection dead, reconnect
- Server should ping too—detects dead clients, cleans up resources
- Idle timeout in proxies (60-120s typical)—heartbeat must be more frequent
- Don't rely on TCP keepalive—too infrequent, not reliable through proxies
Connection State
readyState: 0=CONNECTING, 1=OPEN, 2=CLOSING, 3=CLOSED—check before sending- Buffer messages while CONNECTING—send after OPEN
bufferedAmount shows queued bytes—pause sending if backpressure building- Multiple tabs = multiple connections—coordinate via BroadcastChannel or SharedWorker
Authentication
- Token in URL query:
wss://host/ws?token=xxx—simple but logged in access logs - First message auth: connect, send token, wait for ack—cleaner but more round trips
- Cookie auth: works if same origin—but no custom headers in WebSocket
- Reauthenticate after reconnect—don't assume previous session valid
Scaling Challenges
- WebSocket connections are stateful—can't round-robin between servers
- Sticky sessions: route by client ID to same server—or use Redis pub/sub for broadcast
- Each connection holds memory—thousands of connections = significant RAM
- Graceful shutdown: send close frame, wait for clients to reconnect elsewhere
Nginx/Proxy Config
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_read_timeout 3600s;
- Without these headers, upgrade fails—connection closes immediately
proxy_read_timeout must exceed your ping interval—default 60s too short- Load balancer health checks: separate HTTP endpoint, not WebSocket
Close Codes
- 1000: normal closure; 1001: going away (page close)
- 1006: abnormal (no close frame received)—usually network issue
- 1008: policy violation; 1011: server error
- 4000-4999: application-defined—use for auth failure, rate limit, etc.
- Always send close code and reason—helps debugging
Message Handling
- Text frames for JSON; binary frames for blobs/protobuf—don't mix without framing
- No guaranteed message boundaries in TCP—but WebSocket handles framing for you
- Order preserved per connection—messages arrive in send order
- Large messages may fragment—library handles reassembly; set max message size server-side
Security
- Validate Origin header on handshake—prevent cross-site WebSocket hijacking
- Same-origin policy doesn't apply—any page can connect to your WebSocket server
- Rate limit per connection—one client can flood with messages
- Validate every message—malicious clients can send anything after connecting
Common Mistakes
- No heartbeat—connection appears alive but is dead; messages go nowhere
- Reconnect without backoff—hammers server during outage, prolongs recovery
- Storing state only in connection—lost on reconnect; persist critical state externally
- Huge messages—blocks event loop; stream large data via chunking
- Not handling
bufferedAmount—memory grows unbounded if client slower than server
