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Context Filter

Context filter is applied to the event context. A CloudEvent from Webhook event-source has payload structure as:

{
    "context": {
      "type": "type_of_event_source",
      "specversion": "cloud_events_version",
      "source": "name_of_the_event_source",
      "id": "unique_event_id",
      "time": "event_time",
      "datacontenttype": "type_of_data",
      "subject": "name_of_the_configuration_within_event_source"
    },
    "data": {
      "header": {},
      "body": {},
    }
}

Fields

Context filter has following fields:

filters:
  context:
    type: event_type
    subject: event_subject
    source: event_source
    datacontenttype: event_data_content_type

You can also specify id, specversion and time fields in the YAML manifest, but they are ignored in filtering.

Note It could be useless to build a context filter based on datacontenttype, source and subject as currently they come fixed from event-source:

  • datacontenttype is always application/json
  • source corresponds to eventSourceName specified in the Sensor YAML manifest
  • subject corresponds to eventName specified in the Sensor YAML manifest

How it works

Specify one or more of the available context fields:

apiVersion: argoproj.io/v1alpha1
kind: Sensor
metadata:
  name: with-ctx-filter
spec:
  template:
    serviceAccountName: operate-workflow-sa
  dependencies:
    - name: test-dep
      eventSourceName: webhook
      eventName: example
      filters:
        context:
          source: custom-webhook

Practical example

  1. Create a webhook event-source

    kubectl -n argo-events apply -f https://raw.githubusercontent.com/argoproj/argo-events/stable/examples/event-sources/webhook.yaml

  2. Create a webhook sensor with context filter

    kubectl -n argo-events apply -f https://raw.githubusercontent.com/argoproj/argo-events/stable/examples/sensors/filter-with-context.yaml

  3. Send an HTTP request to event-source

    curl -d '{"message":"this is my first webhook"}' -H "Content-Type: application/json" -X POST http://localhost:12000/example

  4. You will notice in sensor logs that the event is invalid as the sensor expects custom-webhook as the value of the source

Further examples

You can find some examples here.

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