Event Handler

An event handler processes incoming messages and performs actions based on the event's details. Events can trigger various actions, such as:

• Complete Task
• Terminate Workflow
• Update Variables
• Fail Task
• Start Workflow

Event Handler Configuration

Prerequisite

Ensure the necessary message broker is integrated with Orkes Conductor to receive events.

Once the integration is complete, the next step is to configure an event handler.

To configure via UI:

1. Navigate to Event Handler from the left menu on your Orkes Conductor cluster.
2. Click + Define event handler from the top-right corner.
3. Enter the following parameters:

Parameter	Description
name	The name of the event handler.
description	A description of the event handler.
event	The event queue sink in the format: Type : Config Name : Queue/Topic Name. Where, Type - The message broker type where the payload is being received. Supported types include: amqp sqs azure kafka nats gcppubsub ibm_mq Config Name - The integration name added to the cluster. Queue/Topic Name - The name of the queue or topic where the payload is being received. The UI drop-down lists only the integration added to your Orkes Conductor cluster. Select the required integration and ensure you append the topic/queue name. Failure to do so may result in execution errors, as the payload won't have a valid destination.
condition	ECMAScript (JavaScript) function to control message processing. The function should return true for the message to be processed.
evaluatorType	The type of evaluator for the condition. Set to javascript by default.
actions	Array of actions to perform. Each action requires specific input parameters. Supported actions: complete_task terminate_workflow update_workflow_variables fail_task start_workflow
active	Set to true to enable the event handler or false to disable it.

This is the JSON schema for the event handler.

{
 "name": "sample-event-handler",
 "description": "Sample event handler",
 "event": "message-type:integration-name:queue/topic-name",
 "evaluatorType": "javascript",
 "condition": "true",
 "actions": [
  // action payload
 ]
}

To configure an event handler via the API, use the POST /api/event endpoint with the following JSON payload:

{
 "name": "<NAME of the EVENT HANDLER>",
 "event": "<MESSAGE_TYPE>:<CONFIG_NAME>:<QUEUE_OR_TOPIC_NAME>",
 "condition": "true",
 "actions": [
   {
     "action": "<ACTION>",
     <ACTION INPUT PARAMS>, //Input Params based on the action
     "expandInlineJSON": false
   }
 ],
 "active": true,
 "evaluatorType": "javascript",
 "createdBy": "john.doe@acme.com"
}

Using Conditions to Filter Events

You can use ECMAScript expressions to filter events based on their payload.

Example Payload

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

The following expressions can be used in condition with the indicated results:

Expression	Result
$.version > 1	true
$.version > 10	false
$.metadata.length == 300	true

note

To reference the entire payload, use ${$}.

Actions

Based on the events received, several actions can be triggered in Orkes Conductor.

Complete Task​

Marks a task as completed. It can be done using two methods:

• Using workflowId + TaskRefName
• Using taskId

Example Payload

Using workflowId + TaskRefName

{
 "name": "sample-event-handler",
 "description": "Sample event handler",
 "event": "kafka:sampleConfig:sampleName",
 "evaluatorType": "javascript",
 "condition": "true",
 "actions": [
   {
     "action": "complete_task",
     "expandInlineJSON": false,
     "complete_task": {
       "workflowId": "${workflowId}",
       "taskRefName": "${taskReferenceName}",
       "output": {
         "ket": "value"
       }
     }
   }
 ]
}

Using taskId

{
 "name": "sample-event-handler",
 "description": "Sample event handler",
 "event": "kafka:sampleConfig:sampleName",
 "evaluatorType": "javascript",
 "condition": "true",
 "actions": [
   {
     "action": "complete_task",
     "expandInlineJSON": false,
     "complete_task": {
       "taskId": "${taskId}",
       "output": {
         "key": "value"
       }
     }
   }
 ]
}

Parameter	Description
actions.action	Specifies the action to be triggered on receiving events. Set this to complete_task.
actions.complete_task.workflowId	The ID of the workflow that contains the task to be completed (required if using workflowId + taskRefName method).
actions.complete_task.taskRefName	The reference name of the task to be marked as completed (required if using workflowId + taskRefName method).
actions.complete_task.taskId	The task execution ID of the task to be marked as completed (required if using taskId method).
actions.complete_task.output	The output data to be sent along with the completion. Can be string, number, boolean, null, or object/array.

Terminate Workflow​

Terminates a running workflow.

Example Payload

{
 "name": "sample-event-handler",
 "description": "Sample event handler",
 "event": "kafka:sampleConfig:sampleName",
 "evaluatorType": "javascript",
 "condition": "true",
 "actions": [
   {
     "action": "terminate_workflow",
     "expandInlineJSON": false,
     "terminate_workflow": {
       "workflowId": "${event.payload.workflowId)",
       "terminationReason": "A termination reason"
     }
   }
 ]
}

Parameter	Description
actions.action	Specifies the action to be triggered on receiving events. Set this to terminate_workflow.
actions.terminate_workflow.workflowId	The ID of the workflow to be terminated.
actions.terminate_workflow.terminationReason	The reason for terminating the workflow.

Update Variables​

Updates variables in a running workflow. Useful for controlling inputs in a long-running workflow.

Example Payload

{
 "name": "sample-event-handler",
 "description": "Sample event handler",
 "event": "kafka:sampleConfig:sampleName",
 "evaluatorType": "javascript",
 "condition": "true",
 "actions": [
   {
     "action": "update_workflow_variables",
     "expandInlineJSON": false,
     "update_workflow_variables": {
       "workflowId": "${targetWorkflowId}",
       "appendArray": true,
       "variables": {
         "key": "value"
       }
     }
   }
 ]
}

Parameter	Description
actions.action	Specifies the action to be triggered on receiving events. Set this to update_workflow_variables.
actions.update_workflow_variables.workflowId	The ID of the workflow whose variables need to be updated.
actions.update_workflow_variables.appendArray	If true, all list (array) variables in the workflow will be treated as append instead of replace. This can be used to collect data from a series of events into a single workflow.
actions.update_workflow_variables.variables	The variables to be updated in the workflow. Can be string, number, boolean, null, or object/array.

Fail Task​

Marks a task as failed. It can be done using two methods:

• Using workflowId + TaskRefName
• Using taskId

Example Payload

Using workflowId + TaskRefName

{
 "name": "sample-event-handler",
 "description": "Sample event handler",
 "event": "kafka:sampleConfig:sampleName",
 "evaluatorType": "javascript",
 "condition": "true",
 "actions": [
   {
     "action": "fail_task",
     "expandInlineJSON": false,
     "fail_task": {
       "workflowId": "${workflowId}",
       "taskRefName": "${taskReferenceName}",
       "output": {
         "key": "value"
       }
     }
   }
 ]
}

Using taskId

{
 "name": "sample-event-handler",
 "description": "Sample event handler",
 "event": "kafka:sampleConfig:sampleName",
 "evaluatorType": "javascript",
 "condition": "true",
 "actions": [
   {
     "action": "fail_task",
     "expandInlineJSON": false,
     "fail_task": {
       "taskId": "${taskId}",
       "output": {
         "key": "value"
       }
     }
   }
 ]
}

Parameter	Description
actions.action	Specifies the action to be triggered on receiving events. Set this to fail_task.
actions.complete_task.workflowId	The ID of the workflow that contains the task to be failed (required if using workflowId + taskRefNamemethod).
actions.complete_task.taskRefName	The reference name of the task to be marked as failed (required if using workflowId + taskRefNamemethod).
actions.complete_task.taskId	The task execution ID of the task to be marked as failed (required if using taskId method).
actions.complete_task.output	The output data to be sent along with the completion. Can be string, number, boolean, null, or object/array.

Start Workflow

Starts a new instance of a workflow.

Example Payload

{
 "name": "sample-event-handler",
 "description": "Sample event handler",
 "event": "kafka:sampleConfig:sampleName",
 "evaluatorType": "javascript",
 "condition": "true",
 "actions": [
   {
     "action": "start_workflow",
     "start_workflow": {
       "name": "workflow-name",
       "version": "1",
       "correlationId": "1234",
       "idempotencyKey": "xxxxxx",
       "input": {
         "key": "value"
       },
       "taskToDomain": {
         "key": "value"
       },
       "idempotencyStrategy": "RETURN_EXISTING"
     },
     "expandInlineJSON": false
   }
 ]
}

Parameter	Description
actions.action	Specifies the action to be triggered on receiving events. Set this to start_workflow.
actions.start_workflow.name	The name of the workflow to be started.
actions.start_workflow.version	The version of the workflow to be started.
actions.start_workflow.correlationId	A unique identifier for the workflow execution, used for correlating related workflows.
actions.start_workflow.idempotencyKey	A unique key to prevent conflicts with other workflow instances.
actions.start_workflow.idempotencyStrategy	The idempotency strategy determines how to handle duplicate requests: RETURN_EXISTING will return the existing workflow if one with the same idempotency key exists, while FAIL will reject the request if a workflow with that idempotency key has already been triggered.
actions.start_workflow.input	The input data to be passed to the new workflow. Can be string, number, boolean, null, or object/array.
actions.start_workflow.taskToDomain	A mapping of task reference names to domain-specific values. This can be used to define task-specific data or configurations.