Implementing Service Level Objectives

Chapter 14. SLO Evolution

Alex Hidalgo

Service level objectives work best when you’re willing to let them change and grow as your service does. The reality is that your service will change over time, be it in terms of increased or decreased use, changes in the performance of your dependencies, the retirement of old hardware/introduction of new hardware, or shifting expectations of behavior from your users. When these things change, your SLOs should change with them.

Additionally, even if there are no drastic shifts, you’re not always going to be able to pick the correct targets—especially when you’re first starting out. Until you’ve been analyzing your measurements for some time, you can’t be entirely certain that the targets you’ve set for yourself are reasonable.

Finally, you can use aspirational SLOs when you know that your service is in a bad state and that your users are unhappy. Use SLOs to drive change! In these cases, you should be using the immediate error budget burn as a signal to your team and others that reliability work needs to be a focus. As you improve the reliability of your systems, you can make these targets more stringent in an iterative manner.

Revisiting your SLO definitions may sound like a simple process, but there is quite a lot to consider in order to do so in the most effective manner. There are many reasons why SLOs might have to change, and some of those reasons can’t be predicted. The discussions that surround the process of changing ...