Comparison
Desired statevsReconciliation loop
Desired state
you said three replicas, and every time someone deletes one a fourth appears without anybody being asked.
The recorded intent a controller works towards, held in the control plane rather than in anyone's head. Because it is authoritative, manual changes to the running system are not changes at all — they are deviations that will be undone, sometimes within seconds. This is the single most common shock for someone arriving from virtual machines, where what you did by hand stayed done.
Full entry →Reconciliation loop
something reads the difference between what you asked for and what exists, takes one step to close it, and then does it all again forever.
The pattern every controller implements: observe actual state, compare to desired state, act, repeat. It is level-triggered rather than edge-triggered — it looks at where things are, not at what event just happened — which is why a missed message or a crashed controller is self-healing rather than fatal. It also explains the characteristic feel of these systems: nothing fails outright, things simply stay wrong while something retries, so timeouts and events matter more than error codes.
Full entry →