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Why Am I Getting “Misdirected Request” Errors on Nginx Recently?

The “421 Misdirected Request” error on Nginx has become more common due to changes in modern SSL handling, HTTP/2 protocol behavior, and stricter browser enforcement. Here’s a breakdown of what’s causing it and how to prevent it.

🔍 Common Causes (Updated for 2024–2025)

• HTTP/2 and SNI Conflicts: Modern browsers require precise Server Name Indication (SNI) during SSL handshakes. Without this, upstream servers may reject connections.
• Multiple SSL Domains on Same IP: If server blocks aren’t properly set up for each domain, the wrong SSL cert might respond, triggering a 421 error.
• Let’s Encrypt Renewals: Recently renewed certificates can behave differently, especially if wildcard domains or SANs are involved.
• Improper Proxy Settings: Missing these two lines in your proxy config can cause SSL handshake issues:

  proxy_ssl_server_name on;
  proxy_ssl_name $host;

• Mismatch Between Host Header and Server Block: If the requested domain doesn’t match any server_name, Nginx may route traffic incorrectly.
• Backend or Upstream Server Changes: New security updates or server behaviors may now enforce stricter SSL/SNI matching rules.

✅ How to Prevent “Misdirected Request” Errors

• Always include:

  proxy_ssl_server_name on;
  proxy_ssl_name $host;

  when proxying HTTPS traffic.
• Ensure every domain has a properly defined server_name and SSL certificate.
• Avoid mixing HTTP/2 and HTTP/1.1 in complex reverse proxy setups unless intentional.
• Double-check Let’s Encrypt renewals to ensure the cert still matches upstream expectations.
• Use nginx -t or nginx -T to validate configuration.

Pro Tip: Log errors with error_log /var/log/nginx/error.log notice; for deeper insights into proxy issues.