share data between server applications

You could do it in different ways.

1. You could create some API endpoints so the apps could communicate with each other;
2. You could whitelist each servers IP address and use multiple database connections to grab (and maybe cache, if possible) data to be used as needed;

Personally, independently of the type of information stored on each server, I'd go with option 1 and standardize the communications via an API.

EXACTLY! i want to create some api for applications so they could communicate to each other, but you think is it enough to limit IP whitelist and SSL for security?

how hide apis from anyone except this server application (and only my applications on the servers)?

i think i should create second application on the completely different server (server X), and if server A needs some data from server B, server A send request to server X and server X get needed data from server B and passes them tho server A. has this way any additional benefits?

and how i should use token or key or any thing else so servers recognize/validate requests?

ressan.ir
CI is nice