Comparison
Capacity planningvsCone of uncertainty
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 →Cone of uncertainty
you were asked for a date before anyone had opened the vendor's documentation, and gave one.
The observation that estimates are wildest at the start of a project and narrow as work is done and unknowns are resolved. It is a reason to give ranges rather than points early, and to re-estimate as evidence arrives rather than defending the first number. The practical use in a conversation is to say where on the cone you are: an estimate made before a spike and one made after are different kinds of claim.
Full entry →