1. select a cloud server for MQTT broker, suggest to use Linux server by Amazon AWS or Alibaba cloud.
2. install MQTT broker applicatoin to your server, such as mosquito or EMQ X, chose open source type.
3. allow MQTT ports by cloud server's security group.
4. start MQTT service.
5. set controller's network setting for MQTT Server Domain/IP address, port.
6. use MQTTBox debug tool to send command remote control relay for a testing.
MQTTBox debug tool download:
https://www.kincony.com/download/client_MQTTBox-win.zip
EMQ X: https://www.emqx.com/en/downloads?product=broker