Asserts has curated an assertion library pertaining to our SAAFE model. Internally they are a collection of Prometheus rules with user-configurable thresholds. We divide the threshold configuration into three sections and organize each section by assertion types

  • Request is about rate, latency, and error assertions

    • Each Anomaly is checked against a dynamic range that combines standard deviation and percentage change. Daily and weekly seasonalities are considered. A sparseness check is also implemented to reduce noise on sparse requests.

    • Each Breach is checked against a static threshold. ErrorLogSpike is also a breach assertion

    • Client Errors are treated as anomalies, so follow the anomaly algorithms mentioned above

    • Server Errors are tracked with an error budget approach, so they are controlled by fast-burn or slow-burn factors

  • The Resource section is about CPU, Memory, Disk, Network, etc

    • Each Saturation works with two static thresholds, one for warning and one for critical

    • Some resources like disk have rate metrics (bytes read/write), so we have ResourceRateAnomaly and ResourceRateBreach assertions. They follow the same approach as their request counterparts

  • The Health section is mostly about all the failure assertions in various domains. We organize the domain rules by groups. Within each group, the user can edit each individual rule.

Besides configuring all the default thresholds, the user can also configure individual thresholds on fine-grained levels. These levels are hierarchical. For requests, if you specify a threshold on job level, it applies to all the request types for that job. Similarly, if you specify a threshold on request_type level, it applies to all the request contexts for that request type and job.

For resources, the hierarchy starts with source, i.e., the exporter, then resource_type, and then container. An additional dimension is severity, which is independent of the granularity levels.


As we mentioned earlier, assertions are not alerts. If you want to get notified, you can add notification rules. Asserts uses Prometheus Alert Manager for notification internally, so we support all the receivers listed on its official page (Email, Pagerduty, Slack, etc.)

Notifications are organized into different sections, just like the thresholds, and the same hierarchical granularity levels apply. You can set notifications for an assertion whenever it fires or when it fires on a specific job or a job and request type. Free-form label conditions are also supported here.

There is also a quick shortcut from the Workbench to bring you to the notification settings with all the labels pre-populated.

SLO notifications can also be managed here.


Similar to notifications, you can also choose a subset of assertions to suppress, so they don’t fire. Suppressed assertions are ignored in Asserts processing. They will not be available in Top Insights, Graph, or the Workbench. Note this is very different from an assertion that fires but does not notify.

Bring your own

If you have your own rules, you can also bring them into the Asserts system by defining custom assertion rules. You can add them individually on the UI or upload a rule file.

Entity and Relation

A set of model rules defines Asserts' entity model. Thus, we can extend the model by including more custom rules. There are two model rules: entity rules and relationship rules, and both only rely on Prometheus metrics data. Asserts runs the specified queries and uses the context information in labels to build entities and relationships.

Our default entities rules are carefully curated to cover most scenarios, so we usually do not expect customers to supply additional ones. If you still want to augment the model, you can add your own model rules by uploading a rule file

For example, the kube_job_labels metric from KSM usually has a job_name label to indicate the k8s job name. We could define a Job entity using job_name as its identifier, but job_name often ends with a GUID, so it may not be the ideal name. In this particular case, the customer has a label label_framework_task_name that specifies the name of the framework task that creates all these k8s jobs. Using this task name instead of the job_name works better for them. Hence, they define the custom Job entity with the label_framework_task_name label.

In addition, our Asserts epbf probe also captures k8s job name as the client name in our ebpf connection metrics. We can join this metric with kube_job_labels to get the task name and in turn, establish the ROUTES relationship from each Job to all the Services it talks to.

Quite often, custom rules are about relationships between services. To eliminate the management hassle of custom relationship rules, the Asserts platform supports service calls defined by an asserts:relation:calls metric. For example, customers can add the following recording rule indicating that api-server service calls a shipping service based on the pattern uri=~"/shipping/.*" generated by their app, recorded with http_requests metric.

- record: asserts:relation:calls
  expr: sum by (job, namespace, asserts_env, asserts_site)
         (rate(http_requests{job="api-server", uri=~"/shipping/.*"}[5m]))
    dst_job: shipping
    dst_namespace: back-office

Note this rule is a custom metric, thus not a custom model rule. It should be added in the Bring your own section.


Relabelling rules are used for manipulating labels in the metrics ingestion. They can also be used to rename or drop metrics.

Adding new label

New label can be added with the following relabeling rule:

- target_label: "foo"
  replacement: "bar"

This relabeling rule adds {foo="bar"} label to all the incoming metrics. For example, metric{job="aa"} will be converted to metric{job="aa",foo="bar"}.

Updating existing label

Existing label can be updated with the relabeling rule mentioned above:

- target_label: "foo"
  replacement: "bar"

This rule rewrites metric{foo="aaaa"} with metric{foo="bar"}.

Rewriting existing label

The following relabeling rule can be used for removing port part from instance label:

- source_labels: [instance]
  regex: "([^:]+):.+"
  target_label: "instance"
  replacement: "$1"

This rule translates foo{instance="bar:123"} to foo{instance="bar"}.

How does it work: it extracts instance label value (see source_labels list above), applies the given regex to it, then generates replacement string ($1 is substituted by the part of instance label that is matched by regex part in the first parenthesis), and then puts the replacement string into target_label.

Updating metric name

*Metric name can be updated with the following relabeling rule:

- source_labels: [__name__]
  regex: "(.+)_suffix"
  target_label: "__name__"
  replacement: "prefix_$1"

This rule removes _suffix from metric name and adds prefix_ to it. For example, foo_suffix{bar="aaa"} metric would be substituted with prefix_foo{bar="aaa"} with this relabeling rule.

VictoriaMetrics provides additional action — replace_all, which can be used for replacing all the occurrences of the given pattern with something else. For example, the following relabeling rule substitutes all the . chars with _ chars in metric names:

- action: replace_all
  source_labels: [__name__]
  target_label: "__name__"
  regex: "\\."
  replacement: "_"

Graphite-like metric would be substituted with foo_bar_baz after applying this relabeling rule.

Removing unneeded labels

Sometimes it is needed to remove certain labels before storing metrics in Prometheus or VictoriaMetrics. This can be done with action: labeldrop. The name of the label to drop must be specified as a regular expression in regex . For example, the following relabeling rule drops all the label names starting with foo:

- action: labeldrop
  regex: "foo.+"

This relabeling rule transforms the following metric: metric{job="a",instance="xyz",foobar="baz",foox="aaa"} 123 into: metric{job="a",instance="xyz"} 123

Sometimes it is needed to drop all the labels except of a few label names matching the given regexp. This can be done with action: labelkeep. The following relabeling rule drops all the labels except of __name__ and labels ending with keepme:

- action: labelkeep
  regex: "__name__|.*keepme"

This means that metric{job="aa",foo="bar",letskeepme="aaa"} would be translated to metric{letskeepme="aaa"} with the given relabeling rule.

Removing the specific label value

The following rule removes foo="bar" label value:

- source_labels: [foo]
  regex: "bar"
  target_label: foo
  replacement: ""

For example, metric{foo="bar",baz="x"} becomes metric{baz="x"} after applying this relabeling rule, while metric{foo="xxx"} remains the same.

Removing unneeded metrics

Metrics can be dropped with action: drop. For example, the following relabeling rule drops metric if it contains instance label starting from foobar:

- action: drop
  source_labels: [instance]
  regex: "foobar.+"

This relabeling rule drops the following metrics: foo{instance="foobar1"} foo{instance="foobar2",job="xxx",aaa="bb"}

It doesn’t drop the following metrics: foo{instance="xxx"} foo{instance="abc",job="xyz"}

Sometimes it is easier to specify metrics that needs to be preserved instead of metrics that needs to be dropped. In this case action: keep must be used:

- action: keep
  source_labels: [job]
  regex: "foobar"

This relabeling rule preserves metrics with job label equal to foobar, while other metrics will be dropped.\

How to drop metrics if they contain certain values for multiple labels? Just enumerate these labels in source_labels and then specify the desired regex. Then source_labels contains multiple labels, they are concatenated with ; char before matching the provided regex. For example, the following relabeling rule would drop metric with {job="foo",instance="bar"} labels:

- action: drop
  source_labels: [job, instance]
  regex: "foo;bar"

Dropping metrics on certain condition

Sometimes it is necessary to drop a metric if it contains two labels with identical values. This can be done with drop_if_equal action, which is supported by VictoriaMetrics and vmagent. For example, the following relabeling rule would drop metric if it contains identical label values for real_port and needed_port:

- action: drop_if_equal
  source_labels: [real_port, needed_port]

The rule would drop the following metric: foo{real_port="123",needed_port="123"}

but would keep the following metric: foo{real_port="123",needed_port="456"}

VictoriaMetrics also provides* keep_if_equal* action, which drops metric if its source_labels aren’t equal. This may be useful for filtering out superfluous scrape targets detected by kubernetes_sd_config — see these docs for details.

Modifying label names

Sometimes it is necessary to modify label names. Then action: labelmap can be used for this. For example, the following relabeling rule substitutes foo_ prefix in all the label names with bar_ prefix:

- action: labelmap
  regex: "foo_(.+)"
  replacement: "bar_$1"

Note that the rule leaves the original label untouched in the metric. I.e. the following metric — aa{foo_xx="bb",job="qq"} — is translated to aa{foo_xx="bb",bar_xx="bb",job="qq"} by this relabeling rule.

VictoriaMetrics supports additional action — labelmap_all — which allows substituting specified patterns in label names. For example, the following relabeling rule would substitute all the chars with _ chars in all the label names:

- action: labelmap_all
  regex: "-"
  replacement: "_"

This rule translates foo{a-b="x",qwe-x-zz="aa"} with foo{a_b="x",qwe_x_zz="aa"}.

Constructing a label from multiple existing labels

Suppose a metric has host and port labels, while you need constructing address label with host:port contents. This can be done with the following relabeling rule:

- source_labels: [host, port]
  separator: ":"
  target_label: "address"

This relabeling rule joins host and port label values with : separator and stores the result at target_label.

Sometimes it is necessary to construct a label from parts of existing labels. For example, the url label with http://hostname/path value must be constructed from address and path labels, where address contains hostname:port. This can be done with the following relabeling rule:

- source_labels: [address, path]
  regex: "([^:]+):[^;]+;(.*)"
  replacement: "http://$1/$2"
  target_label: "url"

By default source_labels are joined with ; separator before applying regex to the resulting string. So the resulting string will contain address:port;path value. The given regex matches this string and extracts address and path parts into $1 and $2. Then these values are used for constructing replacement string in the form http://<address>/<path>. Then the resulting string is written into target_label.

Chaining relabeling rules

Relabeling rules can be chained. For example, the following rules add {foo="bar"} label and remove port from instance label:

- replacement: "bar"
  target_label: "foo"
- source_labels: [instance]
  regex: "([^:]+):.*"
  replacement: "$1"
  target_label: "instance"

Arbitrary number of relabeling rules can be chained.

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