Comparison
AutoscalingvsCapacity planning
Autoscaling
the instance count goes up on its own when CPU crosses a threshold, and back down twenty minutes after the spike ends.
Adjusting capacity automatically from a signal such as utilisation or queue depth. It saves money on variable load and absorbs gradual growth. It is not fast: instances take time to start and warm, so autoscaling handles trends, not step changes — for those you need headroom or a queue.
Full entry →Capacity planning
you work out from load tests how much traffic one instance handles, and how many you need for Black Friday.
Determining the resources required to meet demand at a target latency, with headroom for failure and spikes. It requires a measured per-instance capacity, not an assumed one. Plan for the loss of a zone or a region as well as the peak, or your headroom disappears exactly when you need it.
Full entry →