How to resume a workflow execution?

I'm pretty new to workflow concepts and trying to implement few long running processes. I'm trying to understand two things.

**Resuming the workflow**
I want the workflow to be triggered by an event or a set of events. The events are received from the messaging system. I can read the messages and feed it into the workflow to start it but once it is waiting (like stored the state on the provider). At this stage I want certain conditions to be set in the storage to be able trigger the next stage:

a. Does a workflow constantly monitors the intermediate saved state for the changes?
b. Should I insert some event and trigger the event to resume the workflow?
c. Or there is some other way to handle this case ?

**Scalability in cloud**
My Second problem is related to scalability in cloud based system:
Can I run a group of workflow (think of a cluster) in kubernetes to scale it or a provider works with a single workflow engine?