It is not easy to calculate how many simulation servers are needed for a specific load test. How many servers are required depends on many factors, including:
We recommend making several test runs of your performance test. These test runs allow you to collect data that can be helpful in determining the configuration of your DevTest Server environment. Collecting metrics and monitoring memory and CPU usage is invaluable for estimating the number of virtual users you can use on a given simulator server.
The registry is lightweight and requires few computing resources. The registry can be run from virtually any computer in your network.
The coordinator server requires resources. Although the coordinator server does not require its own computer, installing it on a separate computer is a common practice. Follow this practice if you are collecting many metrics, requesting many reports, or both.
Simulator servers are used to simulate thousands of virtual users. We recommend running one simulator server per physical server. Technically, a single simulator server can be started with as many instances as you want. However, server memory size and speed typically limit the number of instances for each simulator. A good upper limit is around 250 virtual users.
Vertical or horizontal scaling can be used for sizing the server. In vertical scaling, you increase CPU speed and available memory, which are typically limited. In horizontal scaling, you add more servers. To increase the number of virtual users, horizontal scaling is recommended.
The number of instances per simulator depends on many factors. A simple rule is not available for calculating the maximum number of instances.
Network latency impacts load and performance. We recommend that the database is housed on a server within the same data center as the major DevTest components.
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