How-To: Use output bindings to interface with external resources

Invoke external systems with output bindings

With output bindings, you can invoke external resources without depending on special SDK or libraries. An output binding represents a resource that Dapr uses to invoke and send messages to. For a complete sample showing output bindings, walk through the tutorial.

This guide uses a Kafka binding as an example. You can find your preferred binding spec from the list of bindings components.

Create a binding

Create a new binding component with the name of checkout.

Within the metadata section, configure Kafka-related properties, such as:

• The topic to which you’ll publish the message
• The broker

Create the following binding.yaml file and save to a components sub-folder in your application directory.

• Self-Hosted (CLI)
• Kubernetes

Use the --components-path flag with dapr run to point to your custom components directory.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: checkout
spec:
  type: bindings.kafka
  version: v1
  metadata:
  # Kafka broker connection setting
  - name: brokers
    value: localhost:9092
  # consumer configuration: topic and consumer group
  - name: topics
    value: sample
  - name: consumerGroup
    value: group1
  # publisher configuration: topic
  - name: publishTopic
    value: sample
  - name: authRequired
    value: "false"

To deploy the following binding.yaml file into a Kubernetes cluster, run kubectl apply -f binding.yaml.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: checkout
spec:
  type: bindings.kafka
  version: v1
  metadata:
  # Kafka broker connection setting
  - name: brokers
    value: localhost:9092
  # consumer configuration: topic and consumer group
  - name: topics
    value: sample
  - name: consumerGroup
    value: group1
  # publisher configuration: topic
  - name: publishTopic
    value: sample
  - name: authRequired
    value: "false"

Send an event (output binding)

Below are code examples that leverage Dapr SDKs to interact with an output binding.

• Dotnet
• Java
• Python
• Go
• JavaScript

//dependencies
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using Dapr.Client;
using Microsoft.AspNetCore.Mvc;
using System.Threading;
//code
namespace EventService
{
    class Program
    {
        static async Task Main(string[] args)
        {
            string BINDING_NAME = "checkout";
            string BINDING_OPERATION = "create";
            while(true)
            {
                System.Threading.Thread.Sleep(5000);
                Random random = new Random();
                int orderId = random.Next(1,1000);
                using var client = new DaprClientBuilder().Build();
                //Using Dapr SDK to invoke output binding
                await client.InvokeBindingAsync(BINDING_NAME, BINDING_OPERATION, orderId);
                Console.WriteLine("Sending message: " + orderId);
            }
        }
    }
}

//dependencies
import io.dapr.client.DaprClient;
import io.dapr.client.DaprClientBuilder;
import io.dapr.client.domain.HttpExtension;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Random;
import java.util.concurrent.TimeUnit;
//code
@SpringBootApplication
public class OrderProcessingServiceApplication {
    private static final Logger log = LoggerFactory.getLogger(OrderProcessingServiceApplication.class);
    public static void main(String[] args) throws InterruptedException{
        String BINDING_NAME = "checkout";
        String BINDING_OPERATION = "create";
        while(true) {
            TimeUnit.MILLISECONDS.sleep(5000);
            Random random = new Random();
            int orderId = random.nextInt(1000-1) + 1;
            DaprClient client = new DaprClientBuilder().build();
          //Using Dapr SDK to invoke output binding
            client.invokeBinding(BINDING_NAME, BINDING_OPERATION, orderId).block();
            log.info("Sending message: " + orderId);
        }
    }
}

#dependencies
import random
from time import sleep    
import requests
import logging
import json
from dapr.clients import DaprClient
#code
logging.basicConfig(level = logging.INFO)
BINDING_NAME = 'checkout'
BINDING_OPERATION = 'create' 
while True:
    sleep(random.randrange(50, 5000) / 1000)
    orderId = random.randint(1, 1000)
    with DaprClient() as client:
        #Using Dapr SDK to invoke output binding
        resp = client.invoke_binding(BINDING_NAME, BINDING_OPERATION, json.dumps(orderId))
    logging.basicConfig(level = logging.INFO)
    logging.info('Sending message: ' + str(orderId))

//dependencies
import (
    "context"
    "log"
    "math/rand"
    "time"
    "strconv"
    dapr "github.com/dapr/go-sdk/client"
)
//code
func main() {
    BINDING_NAME := "checkout";
    BINDING_OPERATION := "create";
    for i := 0; i < 10; i++ {
        time.Sleep(5000)
        orderId := rand.Intn(1000-1) + 1
        client, err := dapr.NewClient()
        if err != nil {
            panic(err)
        }
        defer client.Close()
        ctx := context.Background()
        //Using Dapr SDK to invoke output binding
        in := &dapr.InvokeBindingRequest{ Name: BINDING_NAME, Operation: BINDING_OPERATION , Data: []byte(strconv.Itoa(orderId))}
        err = client.InvokeOutputBinding(ctx, in)
        log.Println("Sending message: " + strconv.Itoa(orderId))
    }
}

//dependencies
import { DaprClient, CommunicationProtocolEnum } from "dapr-client";
//code
const daprHost = "127.0.0.1";
(async function () {
    for (var i = 0; i < 10; i++) {
        await sleep(2000);
        const orderId = Math.floor(Math.random() * (1000 - 1) + 1);
        try {
            await sendOrder(orderId)
        } catch (err) {
            console.error(e);
            process.exit(1);
        }
    }
})();
async function sendOrder(orderId) {
    const BINDING_NAME = "checkout";
    const BINDING_OPERATION = "create";
    const client = new DaprClient(daprHost, process.env.DAPR_HTTP_PORT, CommunicationProtocolEnum.HTTP);
    //Using Dapr SDK to invoke output binding
    const result = await client.binding.send(BINDING_NAME, BINDING_OPERATION, orderId);
    console.log("Sending message: " + orderId);
}
function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

Invoke the output bindings endpoint on a running Dapr instance.

You can also invoke the output bindings endpoint using HTTP:

curl -X POST -H 'Content-Type: application/json' http://localhost:3601/v1.0/bindings/checkout -d '{ "data": 100, "operation": "create" }'

As seen above:

1. The example invoked the /binding endpoint with checkout, the name of the binding to invoke.
2. The payload goes inside the mandatory data field, and can be any JSON serializable value.
3. The operation field tells the binding what action it needs to take. For example, the Kafka binding supports the create operation.

You can check which operations (specific to each component) are supported for every output binding.

Watch this video on how to use bi-directional output bindings.

References

• Binding API
• Binding components
• Binding detailed specifications

Last modified June 23, 2022: Merge pull request #2550 from ItalyPaleAle/cosmosdb-harcoded-dapr-version (cf03237)