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Prerequisites

Knative runtime based functions can also interact with middleware via dapr components just like the Async functions.

In this case, we will create two functions: function-front and kafka-input. function-front will send the content to the kafka after a HTTP request received. The kafka-input will watch the kafka and consume it.

You can refer to the Installation Guide to setup OpenFunction.

Follow this guide to install a Kafka server named kafka-server and a Topic named sample-topic.

Follow this guide to create a registry credential.

Deployment

kafka-input

kafka-input defines an input source (serving.inputs). This input source points to a dapr component of the Kafka server. This means that the kafka-input will be driven by events in the "sample-topic" topic of the Kafka server.

serving:
  runtime: async
  inputs:
    - name: sample
      component: target-topic
      type: bindings
  bindings:
    target-topic:
      type: bindings.kafka
      version: v1
      metadata:
        - name: brokers
          value: "kafka-server-kafka-brokers:9092"
        - name: topics
          value: "sample-topic"
        - name: consumerGroup
          value: "kafka-input"
        - name: publishTopic
          value: "sample-topic"
        - name: authRequired
          value: "false"
  template:
    containers:
      - name: function # DO NOT change this
        imagePullPolicy: IfNotPresent

Use the following command to create the function:

kubectl apply -f ../../../async/java/kafka-input/kafka-input.yaml

function-front

The function plugin mechanism is also demonstrated in function-front, and you can observe the following configuration in the definition of function-front.

apiVersion: core.openfunction.io/v1beta2
kind: Function
metadata:
  name: function-front
  annotations:
    plugins: |
      pre:
      - dev.openfunction.samples.plugins.ExamplePlugin
      post:
      - dev.openfunction.samples.plugins.ExamplePlugin

pre defines the order of plugins that need to be called before the user function is executed

post defines the order of plugins that need to be called after the user function is executed

You can learn about the logic of these two plugins and the effect of the plugins after they are executed here: plugins mechanism

In function-front, we define an output (serving.outputs) that will point to a dapr component definition of the Kafka server.

  serving:
    runtime: knative
    outputs:
      - name: target
        component: kafka-server
        type: bindings
        topic: "sample-topic"
        operation: "create"
    pubsub:
      kafka-server:
        type: bindings.kafka
        version: v1
        metadata:
          - name: brokers
            value: "kafka-server-kafka-brokers:9092"
          - name: authRequired
            value: "false"
          - name: publishTopic
            value: "sample-topic"
          - name: topics
            value: "sample-topic"
          - name: consumerGroup
            value: "function-front"

The custom content will send to the output named target in the function-front function.

For sample function below, modify the spec.image field in function-front.yaml to your own container registry address:

apiVersion: core.openfunction.io/v1beta2
kind: Function
metadata:
  name: function-sample
spec:
  image: "<your registry name>/sample-knative-dapr-java:v1"

Use the following command to create function-front function:

kubectl apply -f function-front.yaml

Demo

Check the current function status:

kubectl get functions.core.openfunction.io

NAME               BUILDSTATE   SERVINGSTATE   BUILDER         SERVING         ADDRESS                                            AGE
function-front     Succeeded    Running        builder-sk9s2   serving-dgqq7   http://function-front.default.svc.cluster.local/   11m
kafka-input-java   Succeeded    Running        builder-29s69   serving-5mrq5                                                            2m21s

The Function.status.addresses field provides various methods for accessing functions. Get Function addresses by running following command:

kubectl get function function-front -o=jsonpath='{.status.addresses}'

You will get the following address:

[{"type":"External","value":"http://function-front.default.ofn.io/"},
{"type":"Internal","value":"http://function-front.default.svc.cluster.local/"}]

You can use the following command to create a pod in the cluster and access the function from the pod:

kubectl run curl --image=radial/busyboxplus:curl -i --tty

Access functions by the internal address:

[ root@curl:/ ]$ curl -d '{"message":"Awesome OpenFunction!"}' -H "Content-Type: application/json" -X POST http://function-front.default.svc.cluster.local/

Access functions by the external address:

To access the function via the Address of type External in Funtion.status, you should configure local domain first, see Configure Local Domain.

[ root@curl:/ ]$ curl -d '{"message":"Awesome OpenFunction!"}' -H "Content-Type: application/json" -X POST http://function-front.default.ofn.io/

Query function-front's log:

kubectl logs -f \
  $(kubectl get po -l \
  openfunction.io/serving=$(kubectl get functions function-front -o jsonpath='{.status.serving.resourceRef}') \
  -o jsonpath='{.items[0].metadata.name}') \
  function

The logs are as follows:

[main] INFO org.eclipse.jetty.server.Server - jetty-11.0.9; built: 2022-03-30T17:44:47.085Z; git: 243a48a658a183130a8c8de353178d154ca04f04; jvm 18.0.1.1+2
[main] INFO org.eclipse.jetty.server.handler.ContextHandler - Started o.e.j.s.ServletContextHandler@-234de47e{/,null,AVAILABLE}
[main] INFO org.eclipse.jetty.server.AbstractConnector - Started ServerConnector@dafe6b9b{HTTP/1.1, (http/1.1)}{0.0.0.0:8080}
[main] INFO org.eclipse.jetty.server.Server - Started Server@b6fa4d5c{STARTING}[11.0.9,sto=0] @2880ms
plugin plugin-example:v1.0.0 exec pre hook for http function at 2022-10-18 08:08:55.Z
receive event: {"message":"Awesome OpenFunction!"}
send to output target
plugin plugin-example:v1.0.0 exec post hook for http function at 2022-10-18 08:08:58.Z

Query kafka-input's log:

kubectl logs -f \
  $(kubectl get po -l \
  openfunction.io/serving=$(kubectl get functions kafka-input-java -o jsonpath='{.status.serving.resourceRef}') \
  -o jsonpath='{.items[0].metadata.name}') \
  function

The logs are as follows:

plugin plugin-example:v1.0.0 exec pre hook for binding serving-922d6-component-target-topic-jpvlq at 2022-10-18 09:55:08.Z
receive event: "{\"message\":\"Awesome OpenFunction!\"}"
plugin plugin-example:v1.0.0 exec post hook for binding serving-922d6-component-target-topic-jpvlq at 2022-10-18 09:55:08.Z