Capacity planning is an important task when trying to anticipate resources and scaling factors for our applications.

The usl4j library offers us an easy abstraction for Neil J. Gunther’s Universal Scalability Law and allows us to build up a predictive model based on the parameters throughput, latency and concurrent operations.

With a basic input set of two of these parameters, we are able to predict how these values change if we change one input parameter so that we can build our infrastructure or systems according to our SLAs.

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When implementing distributed systems, client-server architectures and simple applications with network related functionalities, everything is fine when we’re in the development or in the testing stage because the network is reliable and the communicating systems are not as stressed as they are in production.

But to sleep well we want to validate how resilient we have implemented our systems, how they behave when the network fails, the latency rises, the bandwidth is limited, connections time out and so on.

In the following tutorial I will demonstrate how to set up a testing environment to simulate different classical network problems with a tool named Toxiproxy and I will show how to integrate it with the well known Java testing stack with Maven and JUnit.

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