502 Bad Gateway Error

Verify the upstream server (your app server) is running and responding correctly.

# Check if the upstream server is running
curl -I http://localhost:3000/health
# Should return 200 OK

# Check application process
systemctl status myapp
# or
pm2 status

Ensure the proxy_pass directive points to the correct upstream address and port.

server {
  location / {
    proxy_pass http://localhost:3000;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host $host;
    # Increase timeout if needed
    proxy_read_timeout 60s;
  }
}

Ensure the proxy server can reach the upstream server through any firewalls or security groups.

# Test connectivity from proxy to upstream
telnet upstream-server 3000
# or
nc -zv upstream-server 3000