502 Bad Gateway Checklist

Problem

The final response code for the site is 502 Bad Gateway.

Symptoms

• HTTP Check shows a final status code of 502.
• The edge is reachable, but the actual application response is not valid.
• The failure is intermittent or concentrated on particular routes.

Top 3 Causes

1. The upstream service is unhealthy - The origin app is down or returns invalid responses.
2. Proxy-to-upstream connectivity is broken - Ports, sockets, health checks, or internal routing are wrong.
3. DNS or target routing is incorrect - The proxy forwards requests to the wrong environment or stale upstream.

Diagnose with DechoNet

• HTTP Check to inspect the final code and response path.
• Port Check to verify the expected upstream port is reachable.
• DNS Lookup to confirm the hostname resolves to the intended origin or proxy target.

Resolution Checklist

• Confirm the upstream application is healthy and actually running.
• Review reverse proxy upstream address, port, and health check configuration.
• Verify the origin port is open and reachable within the internal network path.
• Check that the proxy is not targeting an old deployment or the wrong host.
• Re-run HTTP Check and confirm the final response no longer returns 502.

When to Escalate

• Escalate if a managed load balancer or platform ingress controls the upstream path.
• If 502 errors are intermittent, investigate scaling behavior, saturation, and keepalive or timeout settings.