521 Web Server Is Down

521

Web Server Is Down

Example HTTP Response

HTTP Response

HTTP/1.1 521 Web Server Is Down
Server: cloudflare
Content-Type: text/html

<html><body>Web server is down</body></html>

Common Causes

Origin web server is not running (stopped/crashed)
Firewall blocking Cloudflare IP addresses
Origin listening on wrong port
Server overload causing service to stop
Origin IP address changed but Cloudflare DNS not updated
iptables or security group blocking Cloudflare

Technical Details

What does this mean?

Nobody's home! Cloudflare knocked on your server's door but it's locked up tight. Either the server shut down, went on vacation, or is hiding behind the curtains refusing to answer.

Technical Definition

The origin server refused the connection from Cloudflare. The origin's web server is not running or a firewall is blocking Cloudflare.

Code Snippets

Ready-to-use code for returning this HTTP status in your application:

Node.js

// Express.js
app.get('/example', (req, res) => {
  res.status(521).json({
    error: 'Web Server Is Down',
    message: 'Your error message here'
  });
});

// Native HTTP
const http = require('http');

http.createServer((req, res) => {
  res.writeHead(521, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({
    error: 'Web Server Is Down',
    message: 'Your error message here'
  }));
}).listen(3000);

Related Status Codes

🌉502Bad Gateway 🔧503Service Unavailable

521 Web Server Is Down FAQ

What causes a 521 Web Server Is Down error?

Origin web server is not running (stopped/crashed). Firewall blocking Cloudflare IP addresses. Origin listening on wrong port. Server overload causing service to stop. Origin IP address changed but Cloudflare DNS not updated. iptables or security group blocking Cloudflare.

// Express.js app.get('/example', (req, res) => { res.status(521).json({ error: 'Web Server Is Down', message: 'Your error message here' }); }); // Native HTTP const http = require('http'); http.createServer((req, res) => { res.writeHead(521, { 'Content-Type': 'application/json' }); res.end(JSON.stringify({ error: 'Web Server Is Down', message: 'Your error message here' })); }).listen(3000);

521 Web Server Is Down FAQ

What causes a 521 Web Server Is Down error?