Finite State Machines (FSM)
It is an abstract machine that can be in exactly one of a finite number of states at any given time. A state machine is just a specification of how to handle events. It consists of a set of states, one of which is the current state. For each state, we list the events that are significant to that state. For each of those events, we define the new current state of the system.
Let see with an example
Devops: Stable (DB down) --> Critical (DB up) --> Stable (N/w down) --> Warning (N/w up) --> Stable
Here we have defined the states Stable, Critical, Warning and events DB down, DB up, and N/W down. In this case, we have a stable state so whenever our database goes down or the network goes down the state changes to critical/warning. We can link some logic with these states to perform any action for transition.
This logic can help in designing a good program around a problem statement that will have less coupled code and easy to maintain. Cheers!