Splitter

Splitter overview

An event Splitter is part of the TriggerMesh routing solution. It has the simple purpose of splitting JSON arrays into multiple CloudEvents for further processing.

Tip

You can verify that the API is available with the following command:

$ kubectl get crd splitters.routing.triggermesh.io
NAME                               CREATED AT
splitters.routing.triggermesh.io   2021-10-06T09:01:38Z

You can also explore the API specification with:

$ kubectl explain splitter

Splitter tutorial on Kubernetes

Let's create the required objects:

• The sockeye target which serves as an event display.
• The PingSource which produces a JSON array in its payload.
• The Splitter to generate the multiple events.

Event display

First of all, we need to have a tool to see the split events. Create a sockeye service by saving the following YAML manifest in a file called sockeye.yaml and applying it to your Kubernetes cluster:

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: sockeye
spec:
  template:
    spec:
      containers:
        - image: docker.io/n3wscott/sockeye:v0.7.0@sha256:e603d8494eeacce966e57f8f508e4c4f6bebc71d095e3f5a0a1abaf42c5f0e48

kubectl apply -f sockeye.yaml

Open the web interface in a browser at the URL found with the following command:

$ kubectl get ksvc sockeye -o=jsonpath='{.status.url}'

Events producer

Next we create the PingSource which produces CloudEvents that contain a list in their payload. Save the following YAML manifest in a file and apply it to your Kubernetes cluster with kubectl apply.

apiVersion: sources.knative.dev/v1
kind: PingSource
metadata:
  name: ps-splitter-demo
spec:
  schedule: "*/1 * * * *"
  contentType: "application/json"
  data: '{
      "message":"hello",
      "items":[
          {
              "id":5,
              "name":"foo"
          },{
              "id":10,
              "name":"bar"
          }
        ]
      }'
  sink:
    ref:
      apiVersion: routing.triggermesh.io/v1alpha1
      kind: Splitter
      name: splitter-demo

The Splitter

Finally, create the Splitter that will produce two events from every single CloudEvent received from the PingSource by saving the following YAML manifest and applying it to your Kubernetes cluster.

apiVersion: routing.triggermesh.io/v1alpha1
kind: Splitter
metadata:
  name: splitter-demo
spec:
  path: items
  ceContext:
    type: foo.bar.type
    source: splitter
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: sockeye

Note that you define the path where you are going to find a list in the incoming event and you define the CloudEvent attributes of the generated events (i.e splitter as the source and foo.bar.type as the type).

Verify that your splitter is ready with kubectl like so:

$ kubectl get splitter
NAME            ADDRESS                                                          READY   REASON
splitter-demo   http://splitter-adapter.sebgoa.svc.cluster.local/splitter-demo   True

In the sockeye application you will see two individual events that have been generated from the original list emitted by the source. The snapshot below shows you what you should see:

Play with your Splitter as Code

You can play around by modifying the Splitter object and re-applying it with kubectl. This gives you a declarative event splitter which you can manage with your GitOps workflow

Another Splitter example for Kubernetes

apiVersion: routing.triggermesh.io/v1alpha1
kind: Splitter
metadata:
  name: splitter-test
spec:
  path: items
  ceContext:
    type: foo.bar.type
    source: splitter
    extensions:
      key1: value1
      key2: value2
  sink:
    ref:
      apiVersion: eventing.knative.dev/v1
      kind: Broker
      name: default
---
apiVersion: eventing.knative.dev/v1
kind: Broker
metadata:
  annotations:
    eventing.knative.dev/broker.class: MTChannelBasedBroker
  name: default
spec:
---
apiVersion: sources.knative.dev/v1beta2
kind: PingSource
metadata:
  name: ps-splitter-demo
spec:
  contentType: application/json
  data: '{"message":"hello","items":[{"id":5,"name":"foo"},{"id":10,"name":"bar"}]}'
  schedule: '*/1 * * * *'
  sink:
    ref:
      apiVersion: eventing.knative.dev/v1
      kind: Broker
      name: default
---
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: to-splitter
spec:
  broker: default
  filter:
    attributes:
      type: dev.knative.sources.ping
  subscriber:
    ref:
      apiVersion: routing.triggermesh.io/v1alpha1
      kind: Splitter
      name: splitter-test
---
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: sockeye
spec:
  template:
    spec:
      containers:
      - image: docker.io/n3wscott/sockeye:v0.7.0@sha256:e603d8494eeacce966e57f8f508e4c4f6bebc71d095e3f5a0a1abaf42c5f0e48
---
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: to-sockeye
spec:
  broker: default
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: sockeye