Nginx 503 Reverse Proxy Investigation

Context

A QA environment behind an Nginx reverse proxy began returning 503s on a subset of routes.

Problem

The 503 came from Nginx, but the failure could have been Nginx config, upstream service health, or the network path between them. Each layer needed to be ruled in or out.

My role

Investigator: walked the request from edge to upstream and isolated the failing component.

Technical actions

1. [01] Reviewed Nginx access and error logs for the 503 pattern.
2. [02] Validated upstream service health and the proxy_pass target.
3. [03] Checked connectivity and resolution between Nginx and the upstream.

Operational impact

503 traced to its real layer instead of being patched at the wrong one.

What this demonstrates

• Comfort reading reverse-proxy failures end-to-end instead of guessing.