Service level objectives inputs and outputs

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Service Level Objective(s) (SLOs) is a complex term that describes various components of a complex system. This document aims to clarify the inputs and outputs of reliability approaches based on SLOs and how these values are presented in Nobl9. For meaningful comparisons between outputs, they must use the same inputs.

SLO inputs

For correct SLO performance, the following inputs are required:

Service level indicators (SLIs): Metrics that can be used to determine if a system is currently performing in an acceptable state (or not).
Service level objective target: A percentage indicating the desired good state based on SLI status for events or time.
Time window type and duration: The evaluation period for SLIs against the defined SLO target.
Error budget calculation method: To determine your SLO status, two budgeting methods can be applied—event-based or time-based.

SLO outputs

Using a calculation pipeline, based on the four inputs described above, Nobl9 produces the following measures:

Burn rate: The rate at which your service consumes its error budget, calculated as the ratio between observed bad events and allowed bad events within the defined error budget time window. A burn rate value can provide the following insights:
- 1 indicates consumption at the expected pace
- Below 1 suggest budget conservation
- Above 1 signal accelerated budget depletion that may lead to exhaustion
Reliability burn down: The percentage of the time a system has been in a good state, evaluated against the error budget time window.
Remaining error budget: The ratio between the error budget consumed and total error budget multiplied by 100% for clarity:
- Error budget consumed—the difference between the reliability burn down and your SLO target.
- Total error budget—the margin between perfect reliability (100%) and your SLO target.
- For example, when your SLO target is 90% and reliability burn down is 95%, your remaining error budget be as follows: (95%-90%)/(100%-90%)*100=50%

SLO output comparison

To understand your system's performance, you can only compare these outputs if they are calculated using the same inputs.

Nobl9 outputs

On the grid view, Nobl9 displays:

The reliability burn down as a line chart
The remaining error budget in time and a percentage
The burn rate as a natural number

Your SLO details display three charts.

Service level indicator displays incoming SLI data—downsampled or raw. Hover over the chart to know the exact value at any point in time:

In ratio SLOs, SLI chart displays the blue delta line representing the difference between a numerator and denominator.

In threshold SLOs, SLI charts display the SLO target line as follows:

For the ≤ and ≥ target operators, the line is solid
For the < and > target operators, the line is dotted

threshold SLI charts — Threshold SLI charts

Reliability burn down shows the exact reliability burn down value on hover. The dotted line represents your SLO target:

replay source config — Reliability burn down chart

Error budget burn rate also shows the exact value on hover. The dotted line represents 1—the 100% burn rate.

Zooming SLI charts

When zooming in or out of an SLI chart, displayed values may change with the zoom level.

This occurs with sum aggregation on non-incremental ratio SLIs (the Events mode), where values represent the sum of data points per time interval:

Zoom in: Narrower intervals contain fewer data points, resulting in smaller values
Zoom out: Wider intervals capture more data points, producing larger values

Similar behavior can occur with rate aggregation (Events/sec mode) on uneven data streams, where each value is the sum divided by the interval's seconds.

This is how different zoom levels show the same data with different aggregation granularity.