Use Message Service to trigger event-driven workflows - Container Service for Kubernetes

You can use Message Service queues to ingest events from different event sources and trigger workflows in workflow clusters. When an event occurs, such as an Object Storage Service (OSS) event or EventBridge event, the event is delivered to Message Service. Argo then automatically triggers a workflow based on the trigger condition that the event matches.

Prerequisites

Services are activated and features are enabled by performing the steps in the following topics:
- Enable eventing.
- Activate MNS and authorize RAM users to access MNS. Fees are charged for using Message Service. For more information about the billing of Message Service, see Pricing.
A workflow cluster is created and the Alibaba Cloud Argo CLI is downloaded by performing the steps in the following topics:

Step 1: Create an event bus

An event bus can be shared by event-driven workflows in the same namespace. You can use NATS or Message Service to create an event bus. If you already have an event bus, proceed to Step 2: Create an event source.

Use NATS

Create a file named event-bus.yaml. Sample code of the event bus:

apiVersion: argoproj.io/v1alpha1
kind: EventBus
metadata:
  name: default
spec:
  nats:
    native:
      replicas: 3
      auth: token

Run the following command to create an event bus:
```
kubectl apply -f event-bus.yaml
```
Note
After you run the command, an event bus pod is created in the default namespace. Perform the subsequent operations in the same namespace.
Run the following command to check whether the event bus pod runs as normal:
```
kubectl get pod
```

Use Message Service

Log on to the MNS console.
On the Topics page, create a topic named argoeventbus. On the Topic Details page, obtain the endpoint in the Endpoint section.
Log on to the RAM console as a RAM user who has administrative rights.
Create a Resource Access Management (RAM) user and grant the AliyunMNSFullAccess permission to the RAM user. Then, obtain the AccessKey ID and AccessKey secret of the RAM user.
For more information, see Create a RAM user, Grant permissions to a RAM user, Create an AccessKey pair, and View the information about AccessKey pairs of a RAM user.

Run the following command to create a Secret to store the AccessKey pair:

kubectl create secret generic mns-secret\
  --from-literal=accesskey=*** \
  --from-literal=secretkey=***

Create a file named event-bus-mns.yaml and set the parameters to the actual values.

topic: Replace the value with the name of the topic created in Step 2.
endpoint: Replace the value with the endpoint that you obtained in Step 2.

apiVersion: argoproj.io/v1alpha1
kind: EventBus
metadata:
  name: default
spec:
  alimns:
    accessKey:
      key: accesskey
      name: mns-secret
    secretKey:
      key: secretkey
      name: mns-secret
    topic: argoeventbus  # The name of the topic that you created. 
    endpoint: http://165***368.mns.<region>.aliyuncs.com  # The endpoint that you obtained.

Run the following command to apply the event-bus-mns.yaml file to create an event bus:
```
kubectl apply -f event-bus-mns.yaml
```

Step 2: Create an event source

Log on to the MNS console.
On the Queues page, create a queue named test-event-queue and obtain the endpoint in the Endpoint section of the Queue Details page.
Note
If you use Message Service to create the event bus, you can skip steps 3 to 5 and proceed to Step 6.
Log on to the RAM console as a RAM user who has administrative rights.
Create a RAM user and grant the AliyunMNSFullAccess permission to the RAM user. Then, obtain the AccessKey ID and AccessKey secret of the RAM user.
For more information, see Create a RAM user, Grant permissions to a RAM user, Create an AccessKey pair, and View the information about AccessKey pairs of a RAM user.

Run the following command to create a Secret to store the AccessKey pair:

kubectl create secret generic mns-secret\
  --from-literal=accesskey=*** \
  --from-literal=secretkey=***

Create a file named event-source.yaml and set the parameters to the actual values.

topic: Replace the value with the name of the topic that you created in Step 2.
endpoint: Replace the value with the endpoint that you obtained in Step 2.

apiVersion: argoproj.io/v1alpha1
kind: EventSource
metadata:
  name: ali-mns
spec:
  mns:
    example:
      jsonBody: true
      accessKey:
        key: accesskey
        name: mns-secret
      secretKey:
        key: secretkey
        name: mns-secret
      queue: test-event-queue # The name of the queue that you created. 
      waitTimeSeconds: 20
      endpoint: http://165***368.mns.<region>.aliyuncs.com # The endpoint that you obtained.

Run the following command to apply the event-source.yaml file to create an event source:
```
kubectl apply -f event-source.yaml
```
Run the following command to check whether the event source pod runs as normal:
```
kubectl get pod
```

Step 3: Create an event sensor

Create a file named event-sensor.yaml and nest the workflow definition in the event sensor. The following code block shows a sample event sensor:

View sample code

apiVersion: argoproj.io/v1alpha1
kind: Sensor
metadata:
  name: ali-mns
spec:
  template:
    serviceAccountName: default
  dependencies:
    - name: test-dep
      eventSourceName: ali-mns    # Match the name of the event source. 
      eventName: example          # Match the name of the event in the event source. 
  triggers:
    - template:
        name: mns-workflow
        k8s:
          operation: create
          source:
            resource:
              apiVersion: argoproj.io/v1alpha1    # Nest the workflow definition. 
              kind: Workflow
              metadata:
                generateName: ali-mns-workflow-
              spec:
                entrypoint: whalesay
                arguments:
                  parameters:        # Delivery the event content through parameters. 
                    - name: message
                      # this is the value that should be overridden
                      value: hello world
                templates:
                  - name: whalesay
                    inputs:
                      parameters:
                        - name: message
                    container:
                      image: docker/whalesay:latest
                      command: [cowsay]
                      args: ["{{inputs.parameters.message}}"]
          parameters:
            - src:        # Parse the event content and deliver it to the workflow. 
                dependencyName: test-dep
                dataKey: body
              dest: spec.arguments.parameters.0.value

Run the following command to apply the event-sensor.yaml file to create an event sensor:
```
kubectl apply -f event-sensor.yaml
```
Run the following command to check whether the event sensor pod runs as normal:
```
kubectl get pod
```

Note

A Message Service queue is automatically created after the event sensor is created if you use Message Service to create an event bus. The name of the queue is in the ackone-argowf-<namespace>-<sensor-name>-<sensor-uid> format.

Step 4: Send messages to Message Service to trigger the workflow

Log on to the MNS console.
On the Queues page, find the queue named test-event-queue and choose More > Send Messages in the Actions column of the queue.
On the Quick Experience page, enter the message content test trigger argo workflow and click Send Message.

Run the following command to query the status of the workflow in the workflow cluster:

argo list

Expected output:

NAME                     STATUS    AGE   DURATION   PRIORITY
ali-mns-workflow-5prz7   Running   6s    6s         0

Print the workflow log to view the message content.
```
argo logs ali-mns-workflow-5prz7
```
Important
- The workflow name in the command must be the same as the workflow name returned in the previous step. ali-mns-workflow-5prz7 is an example. Replace it with the actual name.
- The message content is encoded by using Base64.
Expected output:

Step 5: Delete event-related resources

Run the following commands to delete event-related resources.
- Delete the event sensor.
```
kubectl delete sensor ali-mns
```
- Delete the event source.
```
kubectl delete eventsource ali-mns
```
- Delete the event bus.
```
kubectl delete eventbus default
```
Run the following command to query the status of the pods. Make sure that all resources are deleted.
```
kubectl get pod
```