Spawning multiple droplets (microservices) accessible by IP address, how to secure traffic by SSL?

Hello, I have the solution that creates and destroys droplets whenever needed - multiple $5 instances that live for a couple of hours max. When these droplets are created - the application installed there immediately notifies my “service discovery” about their IP addresses. My admin/master application can query service discovery - obtain their IP and send them a task to perform.

Service discovery and master application are accessible by domains/subdomains, and these have their Let’s encrypt certificate set.

The problem is - how my master application can speak to these droplets in a secure way. The IP constantly changes as droplets are destroyed and recreated (from snapshot).

Do I need to write a script that creates a self-signed certificate during power up?

I’m aware of private IPs, but worker droplets can be created in different data centers.

Appreciate ideas