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Event Routing

Event routing controls how events flow from EventSources through Sensors to Triggers. Argo Events provides powerful filtering, transformation, and multi-action capabilities. For the complete reference, see the official Sensors documentation.

Event Flow Architecture

Events pass through multiple stages, each providing opportunities to filter, transform, and route:

flowchart LR
    A[EventSource] --> B[EventBus]
    B --> C[Sensor Filter]
    C --> D{Match?}
    D -->|Yes| E[Transform]
    D -->|No| F[Drop]
    E --> G[Trigger]

    %% Ghostty Hardcore Theme
    style A fill:#fd971e,color:#1b1d1e
    style B fill:#515354,color:#f8f8f3
    style C fill:#f92572,color:#1b1d1e
    style E fill:#9e6ffe,color:#1b1d1e
    style G fill:#a7e22e,color:#1b1d1e
    style F fill:#75715e,color:#f8f8f3

Key decision points:

  1. EventSource: Receives raw events, normalizes format, publishes to EventBus
  2. Sensor Filter: Evaluates event data against filter expressions
  3. Transform: Modifies event payload before trigger execution
  4. Trigger: Executes action (workflow, HTTP request, Kubernetes resource)

Routing Patterns

Pattern Use Case Complexity
Simple Filtering Route events based on field values Low
Multi-Trigger Actions Execute multiple actions from one event Medium
Event Transformation Modify payloads before triggering Medium
Conditional Routing Complex decision trees High

Quick Example: Image Tag Filtering

Filter container registry events to only process production tags:

apiVersion: argoproj.io/v1alpha1
kind: Sensor
metadata:
  name: prod-image-filter
spec:
  dependencies:
    - name: image-push
      eventSourceName: container-registry
      eventName: push
      filters:
        data:
          - path: body.tag
            type: string
            value:
              - "v*"
              - "release-*"

This Sensor only triggers when images are pushed with tags starting with v or release-. Development tags like dev-123 or feature-xyz are silently dropped.

Filter Evaluation

Filters are evaluated in order. The first matching filter wins. If no filters match, the event is dropped without triggering any action. Use the Sensor troubleshooting guide to debug filter issues.

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