Understanding what you are buying.
CPU
Measured in cores or virtual cores. Your allocation is reserved, though the underlying physical CPU is shared at the hardware level.
More cores help with concurrent requests and parallel work. They do not make a single slow query faster.
MEMORY
RAM allocated to your machine. This is usually the constraint that bites first.
When memory runs out, the system kills processes to survive. Your database is frequently the casualty, which manifests as the site suddenly failing.
DISK
Storage, and its type matters. SSD or NVMe storage is substantially faster than mechanical disks for database-heavy work.
BANDWIDTH
Data transfer per month. Most sites use far less than they expect.
WHAT TO SIZE FOR
Memory first, then disk type, then CPU. Most VPS performance complaints trace to insufficient memory rather than CPU.
CHECKING YOUR USAGE
Once running, monitor actual usage over a few weeks rather than guessing. It is easy to over-buy and equally easy to under-buy.
