The stress test is fun. In the first place it seems that the objective is to check whether the system is functioning under a given load. In reality, it is common for the system to operate under a given load, but somehow fail when the load is large enough. I call it "hitting the wall" or "bonking". There may be exceptions, but there is almost always a “wall”. The goal of these stress tests is to target where the wall is, and then determine how to push it further.
A stress test plan should be developed early in the project, as this often helps clarify expectations. Two seconds for a web page request, is that a miserable failure or a smashing success? Are 500 simultaneous users enough? It depends, of course, but you have to know the answer when designing the php website development system that meets the demand. The stress test must be realistic enough to be useful. It's not really possible to easily simulate 500 erratic and unpredictable humans using a system simultaneously, but you can at least create 500 simulations and try to model some of what those humans might do.
In a stress test, start with a light load and load in certain dimensions, such as entry rate or entry size, until you "hit the wall." If the wall is too close to meet your needs, target the resource that is the bottleneck (there is usually a dominant one). Is it memory, processor, I / O, network, bandwidth, or data contention? Next, determine how you can move the wall. Note that moving the wall, that is, increasing the maximum load that the system can support, may not help or could adversely affect the performance of a lightly loaded system. Usually, heavy load performance is more important than light load performance.