Occurrences error budget calculation method
The Occurrences method of error budget calculation counts good attempts (for example, requests that are within defined boundaries) against the count of all attempts (i.e., all requests, including requests that perform outside of the defined boundaries).
This method is well suited to measuring recent user experience. Since there are fewer total attempts during low-traffic periods, it automatically adjusts to lower traffic volumes.
Target
Target is used to calculate your error budget. If you want something to be reliable 95% of the time (or in other words, have at most a 5% failure rate over the defined time window), then your target should be set at 95%. This is the reliability target for the service level objective (SLO).
For the Occurrences method, the target defines the percentage of good events to total events that meet the defined target.
Values
Values are the values gathered from the metric source to compare. For example, if Values less than 200 is the objective for a good experience, values below 200 are considered good.
Use case example
Let’s say that you’re looking at traffic on a website that fluctuates throughout the day. During peak load, the service’s performance deteriorates, and some requests fail. There’s also a small performance hiccup during the release due to startup costs, although maintenance is usually planned during low-traffic hours.
Which error budget calculation should you choose - Occurrences or Time Slices?
The Occurrences budgeting method is better suited to this situation. Since total attempts are fewer during low-traffic periods, it automatically adjusts to lower traffic volumes. This method is straightforward and automatically weights impact by the total number of requests served, so it will give an accurate reflection of when your customers’ experience is actually affected.