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How to Fix WebSocket Connection Closed Unexpectedly Error

DodaTech Updated 2026-06-24 3 min read

In this tutorial, you'll learn about How to Fix WebSocket Connection Closed Unexpectedly Error. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

Your WebSocket client receives:

WebSocket connection to 'wss://example.com/socket' failed: Connection closed unexpectedly

Or:

WebSocket onclose event: code 1006, reason: Abnormal Closure

The WebSocket connection was terminated unexpectedly. This can happen due to proxy timeouts, network issues, or server-side disconnections.

Quick Fix

1. Implement automatic reconnection

Add reconnection logic to handle unexpected closures:

// WebSocket with auto-reconnect
class ReconnectingWebSocket {
  constructor(url, options = {}) {
    this.url = url
    this.reconnectInterval = options.reconnectInterval || 3000
    this.maxRetries = options.maxRetries || 10
    this.retries = 0
    this.connect()
  }

  connect() {
    this.ws = new WebSocket(this.url)

    this.ws.onopen = () => {
      this.retries = 0
      console.log('WebSocket connected')
    }

    this.ws.onclose = (event) => {
      if (this.retries < this.maxRetries) {
        setTimeout(() => {
          this.retries++
          this.connect()
        }, this.reconnectInterval * Math.pow(1.5, this.retries))
      }
    }

    this.ws.onerror = (error) => {
      console.error('WebSocket error:', error)
    }
  }

  send(data) {
    if (this.ws.readyState === WebSocket.OPEN) {
      this.ws.send(data)
    }
  }
}

2. Fix proxy timeouts

Proxies and load balancers close idle WebSocket connections:

# Nginx โ€” increase proxy timeout for WebSocket
location /socket/ {
    proxy_pass http://backend:3000;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_read_timeout 86400s;  # 24 hours for <a href="/apis/websocket/">Websocket</a>
    proxy_send_timeout 86400s;
}

3. Implement heartbeat/ping-pong

Keep the connection alive with periodic pings:

// Server-side heartbeat (Node.js with ws)
const WebSocket = require('ws')
const wss = new WebSocket.Server({ port: 8080 })

wss.on('connection', (ws) => {
  ws.isAlive = true
  ws.on('pong', () => { ws.isAlive = true })

  const interval = setInterval(() => {
    if (!ws.isAlive) {
      ws.terminate()
      return
    }
    ws.isAlive = false
    ws.ping()
  }, 30000)

  ws.on('close', () => clearInterval(interval))
})

4. Use WSS (secure WebSocket) in production

Always use wss:// instead of ws:// in production to prevent middleboxes from closing the connection:

// Wrong โ€” unencrypted WebSocket
const ws = new WebSocket('ws://api.example.com/socket')

// Right โ€” encrypted WebSocket
const ws = new <a href="/apis/websocket/">Websocket</a>('wss://api.example.com/socket')

5. Check the WebSocket close code

ws.onclose = (event) => {
  console.log(`Close code: ${event.code}, reason: ${event.reason}`)

  // Common codes:
  // 1000: Normal closure
  // 1001: Going away (server restart)
  // 1006: Abnormal closure (no close frame)
  // 1009: Message too big
  // 1011: Unexpected server error
}

Prevention

  • Always implement reconnection with exponential backoff.
  • Use heartbeats (ping/pong) to keep idle connections alive.
  • Configure proxy timeouts to allow long-lived WebSocket connections.
  • Use WSS to prevent interference from network intermediaries.
  • Monitor WebSocket disconnect rates for early problem detection.

Common Mistakes with WebSocket close

  1. Misunderstanding that String is [Char] with poor performance for large text operations
  2. Using foldl instead of foldl' causing stack overflow on large lists
  3. Forgetting deriving (Show, Eq) on custom data types needed for debugging

These mistakes appear frequently in real-world API code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

### What does WebSocket close code 1006 mean?

Code 1006 means the connection closed abnormally without a close frame. This is the most common error code and usually indicates a network issue, proxy timeout, or server crash.

Why does my WebSocket disconnect after 60 seconds?

Many proxies and load balancers have a 60-second idle timeout. If no data is sent for 60 seconds, the proxy closes the connection. Implement ping/pong to keep it alive.

Can I use WebSocket behind a CDN?

Most CDNs support WebSocket, but you must enable it explicitly. Cloudflare requires "WebSockets" to be enabled in the dashboard. Other CDNs may have specific configuration requirements.

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