How to configure ISPConfig to open a site from a neighboring server without ISPConfig?

Question

linux

Given: Local network, with an external IP, two servers, one of them has ISPConfig 3 installed and sites in PHP, the second one has Redmine and git.
HTTP requests on the router are forwarded to the server with ISPConfig, and all sites work fine from it.
Question: How can I use ISPConfig to open Redmine from the second server at its own web address?
As far as I understand, it is necessary to create a DNS zone in ISPConfig and register an A-record. I did it, but something tells me it's wrong. I would not want to put ISPConfig on both servers and create a multiserver.

Answer 1

Is ISPConfig the NS server for your domain (this.dom)?
Do your users get your domain's DNS responses through ISPConfig? That is, it is used by your users as a DNS server?
If not , then add an A-record "redmine.this.dom" on the DNS server used by the users.
If so , point "redmine.this.dom" to the Redmine IP address available to your users.
Then configure Redmine's (nginx?) web server to accept connections by domain name instead of IP address.
kosatchev : Yeah! This means that your users connect to you over the internet using public DNS, and your ISPConfig is not an NS server for them.
You don't need to create A-records on ISPConfig. You can nail "A my-redmine.com 192.168.0.22" and "redmine.this.dom 192.168.0.22".
Create a redmine.this.dom A-record at the domain registrar in your domain management pointing it to your router.
If you do not have another external IP address for Redmine, then you will need nginx (or another web router) on the router, which can show the user a different page depending on the request - this.dom or redmine.this.dom.
If it is not possible to install nginx on a router, buy an inexpensive VPS from any cloud provider for $3-5 per month and set up nginx on it.