Render 500 JSON output when invoking REST API calls and render 500 HTML output when accessing UI

Hi,

I am running the nginx version: nginx/1.22 as a reverse proxy server and
apache httpd version 2.4.55 as web server on CentOS Linux release 7.9.2009
(Core). Drupal CMS version is 9.5.3 which is a php framework, MySQL DB
version is 8.0.32

User -> https://develop.mydomain.com/user/login
User -> Nginx Reverse Proxy -> Apache Web server -> PHP-FPM -> MySQL DB

1. If MySQL DB is down, then

Render 500 JSON output to REST API Calls for Internal Server error
(https://develop.mydomain.com/apis)
Render 500 html output to UI for Internal Server error (
https://develop.mydomain.com/apis/)

2. PHP-FPM Service is down, then

Render 502 JSON output to REST API Calls for bad gateway
(https://develop.mydomain.com/apis)

Render 502 html output to UI for bad gateway
(https://develop.mydomain.com/apis)

UI Dashboard :- https://develop.mydomain.com/user/login
REST API Call :- https://develop.mydomain.com/apis

Please guide me. Thanks in advance.

Best Regards,

Kaushal