Using Event Handlers

Event handlers process incoming messages from external systems and perform actions based on event details. Events can trigger various actions, such as:

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

Prerequisite

Integrate the required message broker with Orkes Conductor. Refer to the Integration Guides for detailed steps.

Event handler parameters

Configure these parameters for the Event Handler.

Parameter	Description	Required/ Optional
name	A unique name for the event handler.	Required.
description	A description of the event handler.	Optional.
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: 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.	Required.
condition	An ECMAScript (JavaScript) function to control message processing. The function should return true for the message to be processed. Learn more about filtering events.	Required.
evaluatorType	The type of evaluator for the condition. Supports `javascript’.	Required.
actions	An array of actions to perform. Each action requires specific input parameters. Supported actions include: complete_task terminate_workflow update_workflow_variables fail_task start_workflow	Required.
active	Whether the event handler is enabled. Set to true to enable the event handler or false to disable it.	Required.

Using conditions to filter events

Use the 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

Use ${$} to reference the entire payload.

Actions

Multiple actions can be triggered based on the events received. Below are the actions and their configuration details.

Complete Task​

The action to mark a task as completed. There are two methods for marking a task as complete:

• Using workflowId and TaskRefName.
• Using taskId.

Example Payload

Using workflowId and 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	Required/ Optional
actions. action	The action to be triggered on receiving events. Set this to complete_task.	Required.
actions. complete_task. workflowId	The ID of the workflow that contains the task to be completed.	Required if using workflowId and taskRefNamemethod.
actions. complete_task. taskRefName	The reference name of the task to be marked as completed.	Required if using workflowId and taskRefNamemethod.
actions. complete_task. taskId	The task execution ID of the task to be marked as completed.	Required if using taskIdmethod.
actions. complete_task. output	The output data to be sent along with the completion. Can be string, number, boolean, null, or object/array.	Optional.

Terminate Workflow​

The action to terminate 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	Required/ Optional
actions. action	The action to be triggered on receiving events. Set this to terminate_workflow.	Required.
actions. terminate_workflow. workflowId	The ID of the workflow to be terminated.	Required.
actions. terminate_workflow. terminationReason	The reason for terminating the workflow.	Required.

Update Variables​

The action to update 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	Required/ Optional
actions. action	The action to be triggered on receiving events. Set this to update_workflow_variables.	Required.
actions. update_workflow_variables. workflowId	The ID of the workflow whose variables need to be updated.	Required.
actions. update_workflow_variables. appendArray	If set to true, all list (array) variables in the workflow are appended with new values instead of being replaced. This can be used to collect data from a series of events into a single workflow.	Optional.
actions. update_workflow_variables. variables	The variables to be updated in the workflow. Can be string, number, boolean, null, or object/array.	Required.

Fail Task​

The action to mark a task as failed. There are two methods for marking a task as failed:

• Using workflowId and TaskRefName.
• Using taskId.

Example Payload

Using workflowId and 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	Required/ Optional
actions. action	The action to be triggered on receiving events. Set this to fail_task.	Required.
actions. complete_task. workflowId	The ID of the workflow that contains the task to be marked as failed.	Required if using workflowId and taskRefNamemethod.
actions. complete_task. taskRefName	The reference name of the task to be marked as failed.	Required if using workflowId and 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.	Optional.

Start Workflow

The action to start a new workflow instance.

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	Required/ Optional
actions. action	The action to be triggered on receiving events. Set this to start_workflow.	Required.
actions. start_workflow. name	The name of the workflow to be started.	Required.
actions. start_workflow. version	The version of the workflow to be started.	Required.
actions. start_workflow. correlationId	A unique identifier for the workflow execution, used to correlate the current workflow instance with other workflows.	Optional.
actions. start_workflow. idempotencyKey	A unique, user-generated key to prevent duplicate workflow executions. Idempotency data is retained for the life of the workflow execution.	Optional.
actions. start_workflow. idempotencyStrategy	The idempotency strategy for handling duplicate requests. Supported values: RETURN_EXISTING—Return the workflowId of the workflow instance with the same idempotency key. FAIL—Start a new workflow instance only if there are no workflow executions with the same idempotency key. FAIL_ON_RUNNING—Start a new workflow instance only if there are no RUNNING or PAUSED workflows with the same idempotency key. Completed workflows can run again.	Required if idempotencyKey is used.
actions. start_workflow. input	The input data to be passed to the new workflow. Can be string, number, boolean, null, or object/array.	Optional.
actions. start_workflow. taskToDomain	A mapping of task reference names to domain-specific values to route the task to defined workers.	Optional.

Event handler configuration

This is the JSON schema for an 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
 ],
"active": true
}

Configuring an event handler

Using Conductor UI

To configure an event handler:

1. Go to Definitions > Event Handler from the left menu on your Conductor cluster.
2. Click +Define event handler.
3. Configure the event handler parameters.
4. Select Save > Confirm Save.

note

The Event field dropdown lists only the integration added to your Conductor cluster. Select the required integration and append the topic/queue name. Failure to do so may result in execution errors, as the payload won't have a valid destination.

Using API

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"
}