Why a Simple Nginx Change Made All Gateway Requests Return 400 (And How to Fix It)

A production incident caused by replacing two Nginx reverse proxies introduced an upstream name with an underscore, resulting in invalid Host headers and 400 Bad Request responses from Spring Cloud Gateway; the article details the step‑by‑step investigation, evidence from logs, tcpdump, and code, and presents configuration fixes to restore normal operation.

HTTP 400Host headerNginx

0 likes · 15 min read

Why a Simple Nginx Change Made All Gateway Requests Return 400 (And How to Fix It)

Java Captain

Jul 7, 2019 · Backend Development

Root Cause Analysis of HTTP 400 Errors After Spring Boot and Tomcat Upgrade Due to Nginx Host Header Handling

The article investigates why upgrading Spring Boot (and Tomcat) caused massive HTTP 400 errors in production, traces the issue to Nginx forwarding a Host header with an underscore, explains Tomcat's stricter RFC‑compliant validation introduced in version 8.5.31, and provides reproducible steps and remediation guidance.

BackendHTTP 400distributed-tracing

0 likes · 7 min read

Root Cause Analysis of HTTP 400 Errors After Spring Boot and Tomcat Upgrade Due to Nginx Host Header Handling