How does stress test execute?

A stress test starts with a load test, and then additional activity is gradually increased until something breaks. An alternative type of stress test is a load test with sudden bursts of additional activity. The sudden bursts of activity generate substantial activity as sessions and connections are established, where as a gradual ramp-up in activity pushes various values past fixed system limitations.
Ideally, stress tests should incorporate two runs, one with burst type activity and the other with gradual ramp-up to ensure that the system under test will not fail catastrophically under excessive load. System reliability under severe load should not be negotiable and stress testing will identify reliability issues that arise under severe levels of load.
An alternative, or supplemental stress test is commonly referred to as a spike test, where a single short burst of concurrent activity is applied to a system. Such tests are typical of simulating extreme activity where a count down situation exists. For example, a system that will not take orders for a new product until a particular date and time. If demand is very strong, then many users will be poised to use the system the moment the count down ends, creating a spike of concurrent requests and load.