CWM supports the Kafka broker and the AMQP and HTTP protocols for handling events. Events can be either consumed by a workflow running inside CWM (incoming events forwarded by a broker) or produced by a running workflow and forwarded to an external system (outgoing events received by a broker).

Note	It is important to remember that CWM doesn't act as an event broker itself. It provides a means to connect to external brokers to forward messages and events.

For the consume event type, CWM connects to a Kafka broker and listens for a specific event type on a topic. Once an event of the specific type registers to the right topic, CWM retrieves the event data and forwards it to the running workflow. The workflow then executes actions defined inside the Event State and/or runs another workflow execution (if selected).

For the produce event type, a running workflow produces a single event or a set of events which CWM then forwards to the broker and they get published in the right topic.

The Kafka broker will accept every event message format supported by the language-specific SDK as long as a valid content-type is sent. See this Github link for lists of supported formats: https://github.com/cloudevents/spec?tab=readme-ov-file.

For the consume event type, CWM connects to an AMQP broker and listens for a specific event type on a queue. Similarly to the Kafka broker, when an event of the specific type registers to the right queue, CWM retrieves the event data and forwards it to the running workflow. The workflow then executes actions defined inside the Event State and/or runs another workflow execution (if selected).

For the produce event type, a running workflow produces a single event or a set of events which CWM then forwards to the broker and they get published in the right queue.

AMQP brokers will accept every event message format supported by the specific SDK as long as a valid content-type is sent. The lists of supported event formats are available here: https://github.com/cloudevents/spec?tab=readme-ov-file.

For the consume event type, CWM exposes an HTTP endpoint that listens for any incoming events. If an event of a specific type comes, it is forwarded to the running workflow that waits for this event type.

Note	When events are consumed, CWM functions as the destination HTTP server. Therefore, the URL of the CWM server is what you effectively provide as the resource for the given HTTP event type.

Event messages need to be HTTP POST requests, and the message body needs to be in JSON format representing a Cloud Event:

 { "specversion": "1.0", 
"id": "2763482-4-324-32-4", 
"type": "com.github.pull_request.opened", 
"source": "/sensors/tn-1234567/alerts", 
"datacontenttype": "text/xml", 
"data": "<test=\"xml\"/>", 
"contextAttrName": "contextAttrValue" } 

For produce events, a workflow produces an event in the Cloud Event format and CWM forwards it as an HTTP POST request to an HTTP endpoint exposed by an external system. The HTTP endpoint address is a concatenation of the host URL defined in the Resource configuration in CWM and the End point field of the Event definition inside the workflow definition. Inside the resource configuration, you can change the request method to PUT or other, and add key and value pairs as header (in JSON format):

The following topics cover the details of event configuration.

In event configuration, secrets store credentials needed to enable connection to a broker or endpoint exposed by a third-party service that sends or receives events. This includes basic authentication: username and password. The Secret ID that you provide when creating a secret will be referenced when creating a resource, so you need to add a secret beforehand. For details, see Step 1: Create a Kafka secret.

The resource is where you provide all the connection details (including the secret) needed to reach an event broker or endpoint exposed by a third party service. Depending on the broker/protocol you want to use, you can choose among three default event resource types

• system.event.amqp.v1.0.0

• system.event.kafka.v1.0.0

• system.event.http.v1.0.0

Notice that there is a different set of configuration fields for each of them

• For AMQP, provide the ServerDSN in the following format amqp //localhost 5723.

• For Kafka:

  • KafkaVersion: Enter your Kafka version. The standard way to check the Kafka version is to run bin/kafka topics.sh version in a terminal.

  • Brokers: Enter your Kafka broker addresses in the following format ["localhost 9092", "192.168.10.9 9092"].

  • OtherSettings: An editable list with default Kafka setting values. You can modify the values as needed. For details, see the "Kafka Other Settings" table below.

• For HTTP:

  • Produce event types: Fill in the URL field and optionally, Method and Headers (for example, Client ID header name and value as a JSON object).

    Note	The URL needs to be the address of the destination HTTP server, but without the URL path. You will enter the URL path as the End point when configuring the event type.

  • Consume event types: Fill in the URL field with the server URL of your CWM instance, for example, 192.168.10.9 9092.

    Note	Remember to provide the URL of your CWM instance without the URL path (/event/http). You will enter the URL path as the End point when configuring the event type.

To create a new event type, you need to have a resource and secret added to CWM.

The following fields are available when adding an event type:

• Event type name: the name of your event type. It's later referred to inside the workflow definition.

• Resource: a list of resources previously added to CWM.

  • Event source: a fully user-defined entry that will be referenced in the workflow definition. Required for produce event kind.

  • End point: the name of Kafka topic (event stream), AMQP endpoint (terminus), or HTTP URL (Host) path.

    Note	For the HTTP consume event type, provide /event/http as your End point.

  • Select kind: a list consisting of two options: consume or produce event kind.

    Note	The both option is not yet supported for CWM.

  • Start listener (only for consume kind): check it to start listening for the defined event type.

  • Run job (only for consume kind): tick this checkbox if you want to trigger a workflow upon receiving the event. Then select the desired workflow from the list.

Event messages must follow the Cloud Events specification format. A minimum viable event message following the specification will contain the following parameters:

{
  "specversion": "1.0",
  "id": "00001",
  "type": "com.github.pull_request.opened",
  "source": "/sensors/tn-1234567/alerts"
}   

The message can carry additional parameters, such as "datacontenttype", "data", and a correlation context attribute name (contextAttrName in this example) :

  {
  "specversion": "1.0",
  "id": "2763482-4-324-32-4",
  "type": "com.github.pull_request.opened",
  "source": "/sensors/tn-1234567/alerts",
  "datacontenttype": "text/xml",
  "data": "<test data=\"xml\"/>",
  "contextAttrName": "contextAttrValue"
}    

In the workflow definition, there are two major syntactical elements that you use to handle the events for which the workflow will be waiting. These are:

• The Event definition: Used to define the event type and its properties. For example:

{
   "name": "applicant-info",
   "type": "org.application.info",
   "source": "applicationssource",
   "correlation": [
    {
      "contextAttrName": "applicantId"
    }
   ]
}

• The Event state: Used to define actions to be taken when the event occurs. For example:

{
"name": "MonitorVitals",
"type": "event",
"onEvents": [
        {
          "actions": [
            {
              "functionRef": {
                "refName": "uppercase",
                "arguments": {
                  "input": {
                    "in": "patient ${ .patient } has high temperature"
                  }
                }
              }
            }
          ],
          "eventRefs": [
            "HighBodyTemperature"
          ]
        }
      ]
}

Now that we have the event type added, we can create a workflow that registers for this event type and executes an action when the event is received by CWM. To do so, we'll need to:

1. Define the event using an Event definition.

2. Specify the Event state

3. Define the actions to be taken when the event occurs.

As an example, let's take a scenario where a router overheating alarm (an inbound event) triggers a single workflow event state and defines two remediation actions to be executed in response to that state.

{
    "id": "HighRouterTempWorkflow",
    "name": "Router Overheating Alarm Workflow",
    "start": "RemediateHighTemp",
    "events": [
        {
            "kind": "consumed",
            "name": "HighRouterTemp",
            "type": "HighRouterTemp",
            "source": "monitoring.app"
        }
    ],
    "states": [
        {
            "end": {
                "terminate": true
            },
            "name": "RemediateHighTemp",
            "type": "event",
            "onEvents": [
                {
                    "actions": [
                        {
                            "functionRef": {
                                "refName": "DispatchTech",
                                "contextAttributes": {
                                    "RouterIP": "${ .RouterIP }"
                                },
                                "resultEventTimeout": "PT30M"
                            }
                        }
                    ],
                    "eventRefs": [
                        "HighRouterTemp"
                    ]
                },
                {
                    "actions": [
                        {
                            "functionRef": {
                                "refName": "MoveTraffic",
                                "contextAttributes": {
                                    "RouterIP": "${ .RouterIP }"
                                },
                                "resultEventTimeout": "PT30M"
                            }
                        }
                    ],
                    "timeouts": {
                        "actionExecTimeout": "PT60M"
                    }
                }
            ]
        }
    ],
    "version": "1.0.0",
    "description": "Remediate router overheating",
    "specVersion": "0.8"
}

Note	This example is not a complete workflow. It is an example of how to define an event inside a workflow, set a simple state, and then define actions to take in response to that single state. A realistic workflow can define many more states and actions to take in response to each of those states.