Nginx / PHP-FPM random post body content in response - php

Question

I have a problem with my NginX / php-fpm / Laravel stack.
The content of post body randomly appear in the response, producing invalid JSON.
Request example :
POST / HTTP/1.1
Accept: application/json
Content-Type: application/x-www-form-urlencoded; charset=utf-8
Host: host
Connection: close
User-Agent: Paw/3.2.1 (Macintosh; OS X/11.2.1) GCDHTTPRequest
Content-Length: 9
test=test
The Response :
HTTP/1.1 500 Internal Server Error
Server: nginx/1.14.0 (Ubuntu)
Content-Type: application/json
Transfer-Encoding: chunked
Connection: close
Cache-Control: no-cache, private
Date: Tue, 16 Feb 2021 07:46:25 GMT
test=test{"error_message":"The POST method is not supported for this route."}
The error is normal (there is no POST route for this uri). But as you can see, the post body appear in the response. (randomly, 1 out of 5 times the request works fine)
It doesn't come from the Laravel stack, I tested it by setting a var_dump / die on top of the index.php (before Laravel loads) and the same problem happens.
Any insights ?
Thank you.
Ah maybe my NginX config :
server {
access_log /var/log/nginx/access;
error_log /var/log/nginx/error;
root /root/devs/peps/www/public;
index index.php index.html index.htm index.nginx-debian.html;
server_name server_name;
underscores_in_headers on;
location / {
try_files $uri $uri/ /index.php?$query_string;
}
location ~ \.php$ {
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_index index.php;
include fastcgi_params;
fastcgi_param SCRIPT_FILENAME /var/www/html/public$fastcgi_script_name;
fastcgi_param PATH_INFO $fastcgi_path_info;
fastcgi_pass 127.0.0.1:9002;
}
listen [::]:443 ssl;
listen 443 ssl;
ssl_certificate [path to cert]
ssl_certificate_key [path to privkey]
}

Answer 1

I had the same issue and resolved it by disabling nginx caching:
location / {
proxy_no_cache 1;
proxy_cache_bypass 1;
#.......
}