<p>I use k8s nginx ingress controller before my backend, having two instances. When web-cleint sends quite big request to ingress - nginx for POST/PUT/GET request always returns 400 Bad request. Btw, no another explanation or details for this error, or at least it is logged in some place where I cannot find it or identify that  my problem is.</p>
<p>After googling I figured out the recipe to fix this: apply <code>large_client_header_buffers</code> with increased value: that's exactly what I did - now my buffer size is <code>4 256k</code>. But no effect , I still get this error.</p>
<p>Pls give me any idea how to procede this problem</p>

<p>So answer is: nginx is not guilty in described behaviour.
After thoroughly investigation of log of java-app which stands behind nginx this exception was noticed</p>
<pre><code>[INFO ] 2021-05-10 16:20:56.354 --- [io-10104-exec-4] org.apache.juli.logging.DirectJDKLog     : Error parsing HTTP request header
Note: further occurrences of HTTP request parsing errors will be logged at DEBUG level.
 
java.lang.IllegalArgumentException: Request header is too large 
</code></pre>
<p>And because of this detail - <code>Note: further occurrences of HTTP request parsing errors will be logged at DEBUG level.</code> - it was too fleeting to be catch up during fluent observation of log.</p>
<p>Summing up solution was to increase SpringBoot property <code>server.max-http-header-size</code> to to more proper value. Default value was 8 Kb.</p>
