The “upstream status 500” in Kong Gateway means that Kong successfully forwarded the client request to the upstream service (your backend/API), but the upstream service itself responded with a 500 Internal Server Error.

What this typically indicates:

• The issue is with the upstream service, not Kong.
• Kong acted as a proxy and did its job correctly; the 500 came from your backend application.

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Common causes on the upstream (backend) side:

1. Unhandled exceptions (e.g., null pointer, syntax errors).
2. Backend server crashed or restarted.
3. Database connection failures.
4. Application logic bug.
5. Timeouts or memory issues in the backend.

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How to troubleshoot:

1. Check upstream (backend) logs at the time of the 500.
2. Use curl directly on the backend API to verify behavior: curl -i http://<upstream_host>:<port>/<path>
3. Enable debug logging in Kong if you want to trace the request: kong reload exit --conf kong.conf --vv
4. Look in Kong logs:
   • /usr/local/kong/logs/error.log
   • See if Kong shows errors related to the upstream or if it just reports the 500.

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Helpful Kong log fields:

If using Splunk or another log aggregator:

• status: final status returned to client
• upstream_status: status from upstream (i.e. 500)
• upstream_uri: target path Kong used to reach the service
• latencies.proxy, latencies.kong, latencies.request: for performance analysis

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