Self-made certificate between servers. How?

Question

Nginx

There are several cloud VDS. The service on https is spinning on them (all http are redirected to it). The banner system works on another server (another hoster, another domain, no SSL).
Task:
What is the best way to organize https between the service and the banner system?
1) buy on domain banner system SSL?
2) to organize it all on self-signed certificates? (describe pitfalls)
Thank you.

Answer 1

If you communicate with yourself, then it doesn't matter. The level of encryption does not depend on the signing of the certificate.

Answer 2

If communication is between sevys, then raise the certification authority on the server, certify the certificates, add them to the trusted ones on each server and do not forget to add the certification authority

Answer 3

Buy a certificate
If "Organize it all on self-signed certificates?" browsers will block the connection to this server, warning that the connection is untrusted