@startuml

"AMQP Bus" -> "Watcher Applier" : launch_action_plan(action_plan.uuid)
"Watcher Applier" -> "Watcher Database" : action_plan.state=ONGOING
"Watcher Applier" -[#blue]> "AMQP Bus" : notify action plan state = ONGOING
"Watcher Applier" -> "Watcher Database" : get_action_list(action_plan.uuid)
"Watcher Applier" <-- "Watcher Database" : actions
loop for each action of the action flow
create Action
"Watcher Applier" -> Action : instantiate Action object with target resource id\n and input parameters
"Watcher Applier" -> Action : validate_parameters()
"Watcher Applier" <-- Action : OK
"Watcher Applier" -[#blue]> "AMQP Bus" : notify action state = ONGOING
"Watcher Applier" -> Action : preconditions()
"Watcher Applier" <-- Action : OK
"Watcher Applier" -> Action : execute()
alt action is "migrate instance"
Action -> "Nova API" : migrate(instance_id, dest_host_id)
Action <-- "Nova API" : OK
else action is "disable hypervisor"
Action -> "Nova API" : host-update(host_id, maintenance=true)
Action <-- "Nova API" : OK
end
"Watcher Applier" <-- Action : OK
"Watcher Applier" -> "Watcher Database" : action.state=SUCCEEDED
"Watcher Applier" -[#blue]> "AMQP Bus" : notify action state = SUCCEEDED
end
"Watcher Applier" -> "Watcher Database" : action_plan.state=SUCCEEDED
"Watcher Applier" -[#blue]> "AMQP Bus" : notify action plan state = SUCCEEDED

@enduml