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Trigger a Microservice with an Event

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Trigger a Microservice with an Event
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Trigger a Microservice with an Event

Jamie Cawley
Jamie Cawley
May 21, 2021
Created by
Jamie Cawley
October 8, 2020
Intermediate
20 min.
SAP BTP, Kyma runtime, Intermediate, SAP Business Technology Platform, Tutorial, Cloud
Trigger a microservice to run when an event is published into the Kyma runtime.

You will learn

  • How to trigger a microservice with an event
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Prerequisites

This tutorial relies on the Commerce mock application to publish events into the Kyma runtime. After binding the Commerce mock application to the dev Namespace, we will create a service instance of the SAP Commerce Cloud - Events. The service instance will allow for any microservice or lambda function within the dev Namespace to subscribe to these events by defining an event subscription. The subscription pairs an event source, the Commerce mock application, and the event type, order.created, to a subscriber which in this case will be the Go MSSQL API microservice.

Step 1: Clone the Git repository
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  1. Copy the repository URL.

In your browser, navigate to kyma-runtime-extension-samples.

Choose the Code button and choose one of the options to download the code locally, or simply run the following command using your CLI at your desired folder location:

git clone https://github.com/SAP-samples/kyma-runtime-extension-samples
Done
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Step 2: Explore the sample

  1. Open the api-mssql-go directory in your desired editor.

  2. Explore the content of the sample.

  3. Within the internal/api/events.go file you can find the code that handles the consumption of the event data. This code expects to receive a JSON payload containing an orderCode. This function is exposed on the path /orderCodeEvent, which is defined in cmd/api/main.go.

  4. Within the k8s directory you can find the file event.yaml containing the event subscription definition which defines how an event will be consumed. The fields of interest include the following which would have to be altered if a different namespace or application name was used:

Property Description Value
spec.filter.filters.eventType.value The event source and version to subscribe to sap.kyma.custom.mp-commerce-mock.order.created.v1
spec.sink The URI endpoint of the service that receives the event http://api-mssql-go.dev.svc.cluster.local:80/orderCodeEvent
Done
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Step 3: Bind Commerce mock to Namespace

In this step you will bind the mock application to the dev Namespace. This process is used to enable the usage of the APIs and events of the mock application to the bounded Namespace. The API and events will then appear within the Service Catalog of the Namespace.

  1. Open the Kyma runtime console.

  2. Choose the Integration > Applications/Systems menu options.

  3. Choose mp-commerce-mock.

  4. Choose Create Binding.

  5. Choose the dev Namespace.

  6. Choose Create.

    Binding
Done
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Step 4: Create a ServiceInstance

In this step you will create a service instance of the events exposed by the mock application. This is done to enable the consumption of the events within the dev Namespace.

  1. Open the Kyma runtime console.

  2. Choose the dev Namespace.

  3. Choose the Service Management > Catalog menu options.

  4. Choose mp-commerce-mock.

    Service Instance

  5. Choose the SAP Commerce Cloud - Events service plan.

    Service Instance Plan

  6. Choose Add.

    Service Instance Plan

  7. Choose Create to create an instance.

Done
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Step 5: Apply an event subscription
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In this step you will define an event subscription which is used to create a subscriber of an event. This will allow you to specify that your api-mssql-go API application, by referencing its service, should receive the payload of the order.created event.

  1. Apply the subscription by running the following command in the CLI:

    kubectl -n dev apply -f ./k8s/event.yaml

  2. Verify that the subscription was created successfully by running this command:

    kubectl get subscription api-mssql-go-event-sub -n dev -o yaml

    After the event subscription definition, find a status object indicating the status of the related resources:

    status:
  conditions:
  - lastTransitionTime: "2021-05-06T14:54:50Z"
    reason: NATS Subscription active
    status: "True"
    type: Subscription active
  emsSubscriptionStatus: {}
  ready: true
What status indicates that all of the related resources of the subscription are ready?
×
Step 6: Test scenario

With the configuration steps completed, you can now test the scenario to validate that it is working as intended.

  1. Open the mock application in the browser by choosing Configuration > APIRules from the menu.

  2. Choose the Host entry for the commerce-mock APIRule to open it in the browser. This URL should be similar to:
    https://commerce.*******.kyma.shoot.live.k8s-hana.ondemand.com

  3. Choose the Remote APIS tab.

    Test the Scenario

  4. Choose the SAP Commerce Cloud - Events option.

  5. For the Event Topics, choose order.created.v1.

  6. Modify the orderCode value as desired and choose Send Event.

    Test the Scenario

  7. With the Kyma console, choose Configuration > APIRules from the menu.

  8. Choose the Host entry for the fe-ui5-mssql APIRule to open the application in the browser. This should be similar to:
    https://fe-ui5-mssql.*******.kyma.shoot.live.k8s-hana.ondemand.com

  9. You should now see the data received by the event as shown below:

    Test the Scenario
What property of a subscription definition is used to specify the application which publishes the events?
×

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