Imagine we have a hosting containing:

* a search engine running on port 5678 (it's required this port it's open in order to work).
* nginx running on port 80.

When a user connects to our website and search something on it, he is only connecting through port 80, but never through 5678. We can check this running "netstat -an".

**So my question is**: If the client it's never connecting directly with the search engine's port, why we need to keep it open?