Using PromQL

The Prometheus Query Language (PromQL) is the defacto standard for querying Prometheus metric data. PromQL is designed to allow the user to select and aggregate time-series data.

Sysdig Monitor's PromQL support includes all of the features, functions, and aggregations in standard open-source PromQL. The PromQL language is documented at Prometheus Query Basics.

For new functionalities released as part of agent v10.0.0, see Integrate Prometheus Metrics.

Construct a PromQL Query

In the Dashboard Panel, select the PromQL type to query data using PromQL.

Display: Specify a meaningful display name for the legend. The text you enter replaces the metric name displayed in the legend. The default legend title is the metric name.
Query: Enter a PromQL query directly. For example:
```
sum(rate(promraw_go_memstats_heap_released_bytes_total[5m])) by(kubernetes_cluster_name)
```
Specify the following:
- Metrics: Search the desired metric. The field supports auto-complete. Enter the text and the rest of the text you type is predicted so you can filter the metric easily. In the example: promraw_go_memstats_heap_released_bytes_total.
- Segmentation: This is the process of categorizing aggregated data with labels to provide precise control over the data. Choose an appropriate value for segmenting the aggregated PromQL data. In this example, kubernetes_cluster_name.
The PromQL query field supports the following variables. Both the variables are replaced in the UI in real-time.
- $__range: A built-in variable. It represents the time range currently selected in the time navigation. In the Live mode, the value is constantly updated to reflect the new time range.
- $__interval: A built-in variable. It represents a time interval and is automatically configured based on the time range.
Unit and Y-Axes: Specify the unit of scale and display format.
Compare To: (Form-Based) Allows you to compare the current value to historical values. Not supported if Segmentation is specified.
Axes: Determine scale, unit, display format, and gauge for the Y-axes.
Legend: Determine the position of the legend in the Dashboard.
Panel: Specify a name and add details about the panel.
See Create a New Panel for details.

Applying a Dashboard Scope to a PromQL Query

The dashboard scope is automatically applied only to form-based panels. To scope a panel built from a PromQL query, you must use a scope variable within the query. The variable will take the value of the referenced scope parameter, and the PromQL panel will change accordingly.

There are two predefined variables available:

$__interval represents the time interval defined based on the time range. This will help to adapt the time range for different operations, such as rate and avg_over_time, and prevent displaying empty graphs due to the change in the granularity of the data.
$__range represents the time interval defined for the dashboard. This is used to adapt operations like calculating average for a time frame selected.

The following examples show how to use scope variables within PromQL queries.

CPU Used Percent

The following query returns the CPU used percent for all the hosts, regardless of the scope configured at the dashboard level, with a mobile average depending on the time span defined.

avg_over_time(sysdig_host_cpu_used_percent[$__interval])

To scope this query, you must set up an appropriate scope variable. A key step is to provide a variable name that is referenced as part of the query.

In this example, hostname is used as the variable name. The host can then be referenced using $hostname as follows:

avg_over_time(sysdig_host_cpu_used_percent{host_name=$hostname}[$__interval])

Depending on the operator specified while configuring scope values, you might need to use a different operator within the query. If you are not using the correct operator for the scope type, the system will perform the query but will show a warning as the results may not be the expected ones.

Scope Operator	PromQL Filter Operator	Example
is foo is not foo	`=` : Select labels that are exactly equal to the provided string. `!=` : Select labels that are not equal to the provided string.	sysdig_host_cpu_used_percent{host_name=$hostname}
in foo,bar not in foo,bar	`=~`: Select labels that regex-match the provided string. `!~` : Select labels that do not regex-match the provided string.	sysdig_host_cpu_used_percent{host_name=~$hostname}

Enrich Metrics with Labels

Running PromQL queries in Sysdig Monitor by default returns only a minimum set of labels. To enrich the return results of PromQL queries with additional labels, such as Kubernetes cluster name, you need to use a vector matching operation. The vector matching operation in Prometheus is similar to the SQL-like join operation.

Info Metrics

Prometheus returns different information metrics that have a value of 1 with several labels. The information that the info metrics return might not be useful as it is. However, joining the labels of an info metric with a non-info metric can provide useful information, such as the value of metric X across an infrastructure/application/deployment.

Vector Matching Operation

The vector matching operation is similar to an SQL join. You use a vector matching operation to build a PromQL query that can return metrics with information from your infrastructure. Vector matching helps filter and enrich labels, usually adding information labels to the metrics you are trying to visualize.

See Mapping Between Classic Metrics and PromQL Metrics for a list of info metrics.

Example 1: Return a Metric Filtered by Cluster

This example shows a metric returned by an application, say myapp_guage, running on Kubernetes. The query attempts at getting an aggregated value of a cluster, by having one cluster selected in the scope. We assume that previously you have set a $cluster variable in your scope.

To do so, run the following query to return the myapp_guage metrics:

sum (myapp_gauge * on (container_id) kube_pod_container_info{cluster=$cluster})

The query performs the following operations, not necessarily in this order:

The kube_pod_container_info info metrics is filtered, selecting only those timeseries and the associated cluster values you want to see. The selection is based on the cluster label.
The myapp_gauge metric is matched with the kube_pod_container_info metric where the container_id label has the same value, multiplying both the values. Because the info metric has the value 1, multiplying the values doesn't change the result. As the info metric has already been filtered by a cluster, only those values associated with the cluster will be kept.
The resultant timeseries with the value of myapp_gauge are then aggregated with the sum function and the result is returned.

Example 2: Calculate the GC Latency

This example shows calculating the GC latency in a go application deployed on a specific Kubernetes namespace.

To calculate the GC latency, run the following query:

go_gc_duration_seconds * on (container_id,host_mac) group_left(pod,namespace) kube_pod_container_info{namespace=~$namespace}

The query is performing the following operations:

The kube_pod_container_info info metrics are filtered based on the namespace variable.
The metrics associated with go_gc_duration_seconds is matched in a many-to-one way with the filtered kube_pod_container_info .
The pod and namespace labels are added from the kube_pod_container_info metric to the result. The query keeps only those metrics that have the matching container_id and host_mac labels on both sides.
The values are multiplied and the resulting metrics are returned. The new metrics will only have the values associated with go_gc_duration_seconds because the info metric value is always 1.

You can use any Prometheus metric in the query. For example, the query above can be rewritten for a sample Apache metric as follows:

appinfo_apache_net_bytes * on (container_id) group_left(pod, namespace) kube_pod_container_info{namespace=~$namespace}

Example 3: Calculate Average CPU Used Percent in AWS Hosts

This example shows the average CPU used percent per AWS account and region, having the hosts filtered by account and region.

avg by(region,account_id) (sysdig_host_cpu_used_percent  * on (host_mac) group_left(region,account_id) sysdig_cloud_provider_info{account_id=~$AWS_account, region=~$AWS_region})

The query performs the following operations:

Filters the sysdig_cloud_provider_info metric based on the account_id and region labels that come from the dashboard scope as variables.
Matches the sysdig_host_cpu_used_percent metrics with sysdig_cloud_provider_info. Only those metrics with the same host_mac label on both sides are extracted, adding region and account_id labels to the resulting metrics.
Calculates the average of the new metrics by account_id and region.

Formatting

Sysdig Monitor supports percentages only as 0-100 values. In calculated ratios, you can skip multiplying the whole query times 100 by selecting percentage as a 0-1 value.