5xx Server ErrorHTTP Status Code Reference

HTTP 502 Bad Gateway— What It Means, Causes & How to Fix It

The server, while acting as a gateway or proxy, received an invalid response from the upstream server. This often indicates a problem with the backend server, not the gateway itself.

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Common Causes

  • Backend server is down or unreachable
  • Upstream server returned an invalid or malformed response
  • Network issues between the proxy/load balancer and backend
  • Backend server crashed or is being restarted

How to Fix

  1. 1Check if the backend server is running and healthy
  2. 2Review proxy/load balancer logs for connection errors
  3. 3Verify network connectivity between proxy and upstream
  4. 4Restart the backend server if it's unresponsive

Example

HTTP 502 Bad Gateway
GET /app HTTP/1.1 → Nginx (proxy)
→ Nginx tries to reach backend at port 3000
→ Backend is down
→ 502 Bad Gateway

Related Server Error Codes

500

Internal Server Error

501

Not Implemented

503

Service Unavailable

504

Gateway Timeout

505

HTTP Version Not Supported

506

Variant Also Negotiates

507

Insufficient Storage

508

Loop Detected

510

Not Extended

511

Network Authentication Required

Commonly Referenced Status Codes

The most frequently searched HTTP status codes

200OK201Created204No Content301Moved Permanently302Found400Bad Request401Unauthorized403Forbidden404Not Found422Unprocessable Content429Too Many Requests500Internal Server Error503Service Unavailable504Gateway Timeout

Related Tools

HTTP Status LookupAPI Request BuildercURL GeneratorHTTP Header ViewerHTTP Header DiffRedirect Checker