In addition to cloud connectivity, we've been using MQTT for IPC in our Linux IIoT gateways and touchscreen terminals and honestly it's been one of the better architectural decisions we've made. Implementing new components for specific customer use cases could not be easier and the component can be easily placed on the hardware or on cloud servers wherever it fits best.
I don't see how gRPC could be any worse than that.
(The previous iteration before MQTT used HTTP polling and callbacks worked on top of an SSH reverse tunnel abomination. Using MQTT for IPC was kind of an afterthought. The SSH Cthulhu is still in use for everyday remote management because you cannot do Ansible over MQTT, but we're slowly replacing it with Wireguard. I gotta admit that out of all VPN technologies we've experimented with, SSH transport has been the most reliable one in various hostile firewalled environments.)
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