What are your favorite software architecture patterns?

I recently discovered control loops as an architectural pattern, and it made me aware that there are probably more architectures that I’m not aware of. If you have a favorite architecture that you think more people should know about, post here. Here’s my submission as an example:

If you aren’t familiar, control loops manage some piece of state; each loop interval/iteration, they read the current state and the desired state, and if they diverge they try to bring the desired state back in line. Because they are so simple (and because the actual and desired states are typically stored externally) control loops are extremely robust and reliable—if implemented properly they can be killed at any time and when they restart they pick up right where they left off (“resumable”). They also provide fault tolerance / self-healing to a system—if the managed state changes for any reason (including errors), a control loop will try to bring it back to the desired state. If the reconciliation attempt fails, the control loop will retry at the next interval.

Some examples of control loops include systemd and other process managers (they watch processes and make sure the process is in the correct state), Kubernetes controllers (they watch Kubernetes resources and reconcile the actual resource state with the desired state), and embedded systems (which watch some external variable like the temperature of a room and try to reconcile it with the desired temperature e.g., by turning on the furnace or AC).