1.2.3 Closed Loop Versus Open Loop
Open loop systems have many disadvantages due to their lack of feedback from the system. With feedback in a closed loop system, we can more closely manage the state of the system relative to desired goals, such as staying within an SLA or providing an appropriate end-user experience. Closed loop systems provide several advantages over open loop systems:
Disturbance rejection from unforeseen increases in user load.
Predictable per
formance with uncertain service models when a user does not know exactly how the service scales relative to user workload.
Improved reference tracking where resource allocation can closely track what is needed to
provide SLA compliance without overprovisioning.
Closed loop systems are recommended because of these benefits.