How to test the maximum load of a web application?

Question

PHP

Developed a web application (a system for conducting city quests), and the second year, I and several other event organizers use it. Normal load - 25-30 users at the same time.
Now there is an order for an event for 3,000 people.
Now the application is on a VPS (RAM 512 MB, CPU 2000 MHz, CPU cores - 1)
Runs on PHP, SQLITE is used as a database.
In what ways can you evaluate whether the application will "pull" or not such a number of users at the same time?
How are tests done to find weaknesses in the system?

Answer 1

If it will be 3000 people at the same time, then most likely (it’s hard to say without studying the application) you need a large and iron dedicated server with ssd, renting such a server (at least for 1 month) can be expensive, but the fee is fixed, while in the cloud it can wind up loads for a lot of money.
Use the tools that Victor Ablebeam advised , the testing algorithm usually looks something like this:
1 make templates that imitate user actions
2 set up monitoring of the VPS server
3 test
4 study the results
5 optimize the application and / or buy more power
6 if necessary, repeat points 3, 4, 5.

Answer 2

apache-utils ab
jmeter
Yandex.tank
In general, often everything depends on the application itself (what type of processes, what type of requests...).
Start with the simplest:ab -n 3000 -c 100 http://site.com/

Answer 3

https://www.joedog.org/siege-home/

Answer 4

It strongly depends on what kind of application, but my opinion is no, this is hardware at the level of an old smartphone.
As a piece of advice - try to deploy to the cloud and be able to dramatically increase the power of the hardware just for such cases.