There are two servers:
- Local Server
- behind a firewall (DSL Router)
- connected to microcontrollers (actors & sensors)
- Cloud Server
- sends commands to Local Servers
The idea is that the Cloud Server sends commands to the Local Server. E.g. to trigger an actor. If there was no firewall, the best way would be IMHO to have a REST API on the Local Server. Unfortunately configuring a NAT is not an option.
What is the simplest and most common way to solve this?