We often get messages asking how many vCPUs needed for load testing. For example:
I want to do a load test with 500k users. I’m trying to decide how many vCPUs I would need for this, and therefore which plan to go for with Redline13. Please could you advise me on how many users you’d recommend per vCPU.
For some background, AWS talks about Optimizing CPU Options.
Most test usage for vCPUs is dependent on your test and performance of your endpoints. We suggest running your test on a single server, something like a m5.xLarge, which has 4 vCPUs, or m5.2xLarge, which has 8 vCPUs. From here you could get a sense of how many vCPUs you might need once you do the math.
The actual response time of your endpoints can also impact the load test. If your endpoint takes 500ms vs 333ms means you will need more concurrent virtual users to simulate the load.
Check your agents CPU in the test results page. If you scroll down we show agent metrics.
Here is a good example where the test only hits about 10% CPU – we could have added many more users to this test.
Here is an example where the agent was overloaded
As a corollary, sometimes people ask about AWS EC2 Instance Types and what will work best for your load test. Read here for more information. Additionally, you may also be interested in reading a related post about AWS cost estimation.
You can try your own test, with different vCPUs, for free with RedLine13 here. And you’ll find that it’s not that hard to figure out how many vCPUs needed for Load Testing.