define state monitor as a type

Signed-off-by: remzi <[email protected]>

README.md

@@ -224,7 +224,6 @@ bash build rucat_state_monitor.sh
 6. More resource clients: Yarn, Spark standalone, Spark local, rust shuttle etc.
 7. expose spark rpc port and web ui port
 8. Remove all unreachable code by using stronger type.
-9. Define state monitor as a type.
 
 ## Debug
 

rucat_state_monitor/src/config.rs

@@ -8,6 +8,11 @@ pub struct StateMonitorConfig {
     /// Time interval in second for checking engine state
     pub check_interval_secs: u8,
     /// Time interval in second for checking trigger state timeout
+    /// *Trigger* states are expected to exist only for a very short time,
+    /// and then be updated to *InProgress* or *Error* states. However, there is a possibility that
+    /// the state monitor is down when the engine is in *Trigger* state, so we need to set a timeout
+    /// to avoid the engine being stuck in *Trigger* state. State monitor will pick up those timed out engines
+    /// and retrigger them.
     pub trigger_state_timeout_secs: u16,
     pub database: DatabaseConfig,
 }