Use case
Assumptions
Let’s say that your application consists of multiple web servers distributed across five regions in the US, and you need to monitor them together. Traditionally, you would create a separate SLO for each of them and observe how they burn their error budgets independently. However, this wouldn’t give you a holistic view of the entire application’s health.
Overview
You can capture the above-mentioned scenario within a single SLO. To define a composite SLO, you can add multiple objectives with different metrics—in our example, each objective would have a query pointing to a node in a different region. The objectives reflect those aspects of your system that contribute to the state of your composite SLO.
Next, you can set targets for every defined objective. In addition to the error budgets for each objective, Nobl9 generates a composite error budget that will burn depending on the condition of the underlying objectives. Thanks to that, you can think of a composite SLO as an SLO made up of multiple SLIs contributing to a single error budget.
Conclusions
After you create a composite SLO by following the steps described in the Create composite SLOs in the UI section, you will be able to observe an additional error budget in the SLO grid view. This allows you to quickly understand the health of the part of your system that you want to keep an eye on. If any of the underlying SLO objectives starts to burn its error budget, the Composite error budget will also burn.
With the composite SLO’s details view, you can:
- Identify when, exactly, the whole customer experience begins to suffer
- Tell at a glance if you should worry or if it’s just a performance hiccup that can be absorbed by your error budget
