Building Microservices: Designing Fine-Grained Systems

by Sam Newman

Response time/latency How long should various operations take? It can be useful here to measure this with different numbers of users to understand how increasing load will impact the response time. Given the nature of networks, you’ll always have outliers, so setting targets for a given percentile of the responses monitored can be useful. The target should also include the number of concurrent connections/users you will expect your software to handle. So you might say, “We expect the website to have a 90th-percentile response time of 2 seconds when handling 200 concurrent connections per second.” Availability Can you expect a service to be down? Is this considered a 24/7 service? Some people like to look at periods of acceptable downtime when measuring availability, but how useful is this to someone calling your service? I should either be able to rely on your service responding or not. Measuring periods of downtime is really more useful from a historical reporting angle. Durability of data How much data loss is acceptable? How long should data be kept for? This is highly likely to change on a case-by-case basis. For example, you might choose to keep user session logs for a year or less to save space, but your financial transaction records might need to be kept for many years. Once you have these requirements in place, you’ll want a way to systematically measure them on an ongoing basis. You may decide to make use of performance tests, for example, to ensure your system me...

Cross functional requirements