Function Inputs and Outputs

Functions usually have inputs and outputs.

Function Inputs

For a sync function, the input is always the payload of the HTTP request.

For an async function, the input data comes from:

• Any Dapr Input Binding components of the Dapr Bindings Building Block
• Any Dapr Pub/sub brokers components of the Dapr Pub/sub Building Block

Function Outputs

For a sync function, the output can be sent through the HTTP response.

Both sync functions and async functions can send outputs to Dapr components including:

• Any Dapr Output Binding components of the Dapr Bindings Building Block
• Any Dapr Pub/sub brokers components of the Dapr Pub/sub Building Block

For example, here you can find an async function with a cron input binding and a Kafka output binding:

apiVersion: core.openfunction.io/v1beta1
kind: Function
metadata:
  name: cron-input-kafka-output
spec:
  ...
  serving:
    ...
    runtime: "async"
    inputs:
      - name: cron
        component: cron
    outputs:
      - name: sample
        component: kafka-server
        operation: "create"
    bindings:
      cron:
        type: bindings.cron
        version: v1
        metadata:
        - name: schedule
          value: "@every 2s"
      kafka-server:
        type: bindings.kafka
        version: v1
        metadata:
        - name: brokers
          value: "kafka-server-kafka-brokers:9092"
        - name: topics
          value: "sample-topic"
        - name: consumerGroup
          value: "bindings-with-output"
        - name: publishTopic
          value: "sample-topic"
        - name: authRequired
          value: "false"

Here is another async function example that use a Kafka Pub/sub component as input.

apiVersion: core.openfunction.io/v1beta1
kind: Function
metadata:
  name: autoscaling-subscriber
spec:
  ...
  serving:
    ...
    runtime: "async"
    inputs:
      - name: producer
        component: kafka-server
        topic: "sample-topic"
    pubsub:
      kafka-server:
        type: pubsub.kafka
        version: v1
        metadata:
          - name: brokers
            value: "kafka-server-kafka-brokers:9092"
          - name: authRequired
            value: "false"
          - name: allowedTopics
            value: "sample-topic"
          - name: consumerID
            value: "autoscaling-subscriber"

Sync functions can also send output to Dapr output binding components or Pub/sub components, here is an example:

apiVersion: core.openfunction.io/v1beta1
kind: Function
metadata:
  name: function-front
spec:
  serving:
    ...
    runtime: knative
    outputs:
      - name: target
        component: kafka-server
        operation: "create"
    bindings:
      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"