on S1 I've the datapoint STM32_1_OnOff used to start/stop the algorithm on STM32_1, a publisher expose it to M,
the same for S2 where I've the datapoint STM32_2_OnOff,
so M can see the state of STM32_1 and of STM32_2
but to start/stop the algorithm on STM32_1 from M I have 2 way:
Directly from M to STM32_1 using a Modbus datasource, this solution is direct but no security (M is on the cloud ) and some interference using 2 master (M and S1) for the same slave (STM32_1)
Pass through S1 with a publisher and use two different datapoint STM32_1_OnOff and STM32_1_OnOffFromMaster, this solution is undirect but is secure and just one master
I'll try to complete implementation of solution 2) as you suggest.