How to correctly calculate the required capacity of a web server?

Question

System administration

Are there any formulas or tables? What to read on this topic?

Answer 1

1. Conduct 5-10 tests on reference data on any server (preferably with a similar software configuration) with the desired configuration: urls, number of simultaneous connections with known input parameters (by frequency of requests, types, etc.) under load for an extended period of time (~30 minutes each) and watch the memory and CPU usage.
2. After each test, upload the entire site from scratch: database, files, clear all caches.
3. Based on the data obtained, you approximate and draw up a graph of the growth in resource consumption with an increase in the input load.
4. After that, based on the estimated traffic parameters (number of requests per day), calculate the required server configuration (based on the resulting graph, the speed of one CPU thread, the number of CPU threads and the average processing time of a public web request to the resource ).
Thus, get 80-85% accuracy from the real one.
Then, add to this a power margin of 33% (1/3) and get the desired value.

Answer 2

No.
Web servers can carry VERY DIFFERENT software, while operating in VERY DIFFERENT MODES.
Recommendations exist only for individual components, for example, purely for MySQL, without taking into account business logic software.
As a basis, you can take the requirements that are in the documentation for the software that you use.
As a rule, this is at the very beginning of the documentation section.
And secondly:
Modern VPS can change their tariff (and available resources) without reinstalling the service.
You start with the cheapest plan, if you have problems with not having enough resources - just increase the plan (this usually requires a VPS restart, but not always).

Answer 3

find it out nowhere
empirically,
because theoretical calculations in processor cycles and bytes are very complex and require a lot of time and money, and testing will take an hour of everything and for free