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Advanced trigger filters

The advanced trigger filters give you advanced options for more precise event routing. You can filter events by exact matches, prefixes, or suffixes, as well as by CloudEvent extensions. This added control makes it easier to fine-tune how events flow ensuring that only relevant events trigger specific actions.

Advanced trigger filters feature is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

Advanced trigger filters overview

The advanced trigger filters feature adds a new filters field to triggers that aligns with the filters API field defined in the CloudEvents Subscriptions API. You can specify filter expressions, where each expression evaluates to true or false for each event.

The following example shows a trigger using the advanced filters field:

apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: my-service-trigger
spec:
  broker: default
  filters:
    - cesql: "source LIKE '%commerce%' AND type IN ('order.created', 'order.updated', 'order.canceled')"
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: my-service

The filters field contains an array of filter expressions, each evaluating to either true or false. If any expression evaluates to false, the event is not sent to the subscriber. Each filter expression uses a specific dialect that determines the type of filter and the set of allowed additional properties within the expression.

Supported filter dialects

You can use dialects to define flexible filter expressions to target specific events.

The advanced trigger filters support the following dialects that offer different ways to match and filter events:

  • exact

  • prefix

  • suffix

  • all

  • any

  • not

  • cesql

Each dialect provides a different method for filtering events based on a specific criteria, enabling precise event selection for processing.

exact filter dialect

The exact dialect filters events by comparing a string value of the CloudEvent attribute to exactly match the specified string. The comparison is case sensitive. If the attribute is not a string, the filter converts the attribute to its string representation before comparing it to the specified value.

Example of the exact filter dialect
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  ...
spec:
  ...
  filters:
    - exact:
        type: com.github.push

prefix filter dialect

The prefix dialect filters events by comparing a string value of the CloudEvent attribute that starts with the specified string. This comparison is case sensitive. If the attribute is not a string, the filter converts the attribute to its string representation before matching it against the specified value.

Example of the prefix filter dialect
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  ...
spec:
  ...
  filters:
    - prefix:
        type: com.github.

suffix filter dialect

The suffix dialect filters events by comparing a string value of the CloudEvent attribute that ends with the specified string. This comparison is case-sensitive. If the attribute is not a string, the filter converts the attribute to its string representation before matching it to the specified value.

Example of the suffix filter dialect
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  ...
spec:
  ...
  filters:
    - suffix:
        type: .created

all filter dialect

The all filter dialect needs that all nested filter expressions evaluate to true to process the event. If any of the nested expressions return false, the event is not sent to the subscriber.

Example of the all filter dialect
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  ...
spec:
  ...
  filters:
    - all:
        - exact:
            type: com.github.push
        - exact:
            subject: https://github.com/cloudevents/spec

any filter dialect

The any filter dialect requires at least one of the nested filter expressions to evaluate to true. If none of the nested expressions return true, the event is not sent to the subscriber.

Example of the any filter dialect
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  ...
spec:
  ...
  filters:
    - any:
        - exact:
            type: com.github.push
        - exact:
            subject: https://github.com/cloudevents/spec

not filter dialect

The not filter dialect requires that the nested filter expression evaluates to false for the event to be processed. If the nested expression evaluates to true, the event is not sent to the subscriber.

Example of the not filter dialect
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  ...
spec:
  ...
  filters:
    - not:
        exact:
          type: com.github.push

cesql filter dialect

CloudEvents SQL expressions (cesql) allow computing values and matching of CloudEvent attributes against complex expressions that lean on the syntax of Structured Query Language (SQL) WHERE clauses.

The cesql filter dialect uses CloudEvents SQL expressions to filter events. The provided CESQL expression must evaluate to true for the event to be processed.

Example of the cesql filter dialect
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  ...
spec:
  ...
  filters:
    - cesql: "source LIKE '%commerce%' AND type IN ('order.created', 'order.updated', 'order.canceled')"

For more information about the syntax and the features of the cesql filter dialect, see CloudEvents SQL Expression Language.

Conflict with the existing filter field

You can use the filters and the existing filter field at the same time. If you enable the new new-trigger-filters feature and an object contains both filter and filters, the filters field overrides. This setup allows you to test the new filters field while maintaining support for existing filters. You can gradually introduce the new field into existing trigger objects.

Example of filters field overriding the filter field:
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: my-service-trigger
spec:
  broker: default
  # Existing filter field. This will be ignored when the new filters field is present.
  filter:
    attributes:
      type: dev.knative.foo.bar
      myextension: my-extension-value
  # New filters field. This takes precedence over the old filter field.
  filters:
    - cesql: "type = 'dev.knative.foo.bar' AND myextension = 'my-extension-value'"
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: my-service