Summary - Event Handlers

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Link

• https://netflix.github.io/conductor/events/

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Introduction

• Eventing in Conductor provides for loose coupling between workflows and support for producing and consuming events from external systems.
• This includes:
  • Being able to produce an event (message) in an external system like SQS or internal to Conductor.
  • Start a workflow when a specific event occurs that matches the provided criteria.
• Conductor provides SUB_WORKFLOW task that can be used to embed a workflow inside parent workflow.
• Eventing supports provides similar capability without explicitly adding dependencies and provides fire-and-forget style integrations.

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Event Task

• Event task provides ability to publish an event (message) to either Conductor or an external eventing system like SQS.
• Event tasks are useful for creating event based dependencies for workflows and tasks.

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Event Handler

• Event handlers are listeners registered that executes an action when a matching event occurs.
• The supported actions are:
  • Start a Workflow
  • Fail a Task
  • Complete a Task
• Event Handlers can be configured to listen to Conductor Events or an external event like SQS.

Configuration

• Event Handlers are configured via /event/ APIs.

Structure

{
  "name" : "descriptive unique name",
  "event": "event_type:event_location",
  "condition": "boolean condition",
  "actions": ["see examples below"]
}

Condition

• Condition is an expression that MUST evaluate to a boolean value.
• A Javascript like syntax is supported that can be used to evaluate condition based on the payload.
• Actions are executed only when the condition evaluates to true.

Example

• Given the following payload in the message:

  {
  "fileType": "AUDIO",
  "version": 3,
  "metadata": {
     length: 300,
     codec: "aac"
  }
  }

Expression	Result
$.version > 1	TRUE
$.version > 10	FALSE
$.metadata.length == 300	TRUE

Actions

• Start a Workflow

  {
  "action": "start_workflow",
  "start_workflow": {
      "name": "WORKFLOW_NAME",
      "version": <optional>
      "input": {
          "param1": "${param1}" 
      }
  }
  }

• Complete Task

  {
  "action": "complete_task",
  "complete_task": {
    "workflowId": "${source.externalId.workflowId}",
    "taskRefName": "task_1",
    "output": {
      "response": "${source.result}"
    }
  },
  "expandInlineJSON": true
  }

• Fail Task

  {
  "action": "fail_task",
  "fail_task": {
    "workflowId": "${source.externalId.workflowId}",
    "taskRefName": "task_1",
    "output": {
      "response": "${source.result}"
    }
  },
  "expandInlineJSON": true
  }

• Input for starting a workflow

• output when completing / failing task follows the same expressions used for wiring workflow inputs.

• Expanding stringified JSON elements in payload

• expandInlineJSON property, when set to true will expand the inlined stringified JSON elements in the payload to JSON documents and replace the string value with JSON document.

• This feature allows such elements to be used with JSON path expressions.

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Extending

• Provide the implementation of EventQueueProvider.
• SQS Queue Provider: SQSEventQueueProvider.java

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Check It

• RabbitMQ ?
  • This could be possible and also simple
  • Extends EventQueueProvider and implements RabbitMQEventQueueProvider
  • How to add rabbitmq event to structure?
  • How to extend location to support multiple queues?
• Condition
  • How Condition works?