Rightsizing

Most instance sizes are set once, at launch, from a guess made before real traffic existed — and then never revisited, because a running system that isn't on fire doesn't generate a reason to go back and check. The gap between provisioned and used capacity grows quietly for as long as nobody looks, and by the time someone does look it's often large enough to embarrass whoever picked the original size.

Rightsizing is not a one-time correction. Usage changes with every feature release, traffic pattern shift, and dependency change, so a size that was correct six months ago is a guess again today. The discipline is the measurement loop, not the resize itself.

Size from what the system actually uses, not from what someone guessed it might need.

1. Size from measured usage, never from instinct

"This feels like it needs 4 vCPUs" is not data. Pull actual CPU, memory, disk, and network utilization over a representative window before changing anything — a resize based on a hunch is just as likely to be wrong in the expensive direction as the cheap one.