Not suitable for server mode

[jimlius]

Putting the program on a cloud server to listen to local devices cannot read the device's data because the cloud uses a listening mode. When the device connects, it actively sends a Modbus command to read the value of the specified address, but the corresponding command API cannot be found

[steveohara]

I'm not really sure what the context is here. I assume you mean that you are running a Slave on a port (your choosing) and that your Cloud provider is waiting for actual connections before it connects. This shouldn't have any effect on j2mod.
The Slave binds to 0.0.0.0 (all adapters) so perhaps this is a firewall, LB, security group issue? There's certainly nothing preventing j2mod from running on Cloud servers.