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How-To: Invoke services using HTTP

Call between services using service invocation

This article describe how to deploy services each with an unique application ID, so that other services can discover and call endpoints on them using service invocation API.

Example:

The below code examples loosely describes an application that processes orders. In the examples, there are two services - an order processing service and a checkout service. Both services have Dapr sidecars and the order processing service uses Dapr to invoke the checkout method in the checkout service.

Diagram showing service invocation of example service

Step 1: Choose an ID for your service

Dapr allows you to assign a global, unique ID for your app. This ID encapsulates the state for your application, regardless of the number of instances it may have.



dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 dotnet run

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 dotnet run

If your app uses an SSL connection, you can tell Dapr to invoke your app over an insecure SSL connection:


dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --app-ssl dotnet run

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --app-ssl dotnet run



dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 mvn spring-boot:run

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 mvn spring-boot:run

If your app uses an SSL connection, you can tell Dapr to invoke your app over an insecure SSL connection:


dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --app-ssl mvn spring-boot:run

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --app-ssl mvn spring-boot:run



dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 -- python3 CheckoutService.py

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 -- python3 OrderProcessingService.py

If your app uses an SSL connection, you can tell Dapr to invoke your app over an insecure SSL connection:


dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --app-ssl -- python3 CheckoutService.py

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --app-ssl -- python3 OrderProcessingService.py



dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 go run CheckoutService.go

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 go run OrderProcessingService.go

If your app uses an SSL connection, you can tell Dapr to invoke your app over an insecure SSL connection:


dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --app-ssl go run CheckoutService.go

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --app-ssl go run OrderProcessingService.go



dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 npm start

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 npm start

If your app uses an SSL connection, you can tell Dapr to invoke your app over an insecure SSL connection:


dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --app-ssl npm start

dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --app-ssl npm start


Set an app-id when deploying to Kubernetes

In Kubernetes, set the dapr.io/app-id annotation on your pod:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: <language>-app
  namespace: default
  labels:
    app: <language>-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: <language>-app
  template:
    metadata:
      labels:
        app: <language>-app
      annotations:
        dapr.io/enabled: "true"
        dapr.io/app-id: "orderprocessingservice"
        dapr.io/app-port: "6001"
...

If your app uses an SSL connection, you can tell Dapr to invoke your app over an insecure SSL connection with the app-ssl: "true" annotation (full list here)

Step 2: Invoke the service

To invoke an application using Dapr, you can use the invoke API on any Dapr instance.

The sidecar programming model encourages each application to interact with its own instance of Dapr. The Dapr sidecars discover and communicate with one another.

Below are code examples that leverage Dapr SDKs for service invocation.


//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)
        {
           while(true) {
                System.Threading.Thread.Sleep(5000);
                Random random = new Random();
                int orderId = random.Next(1,1000);
                CancellationTokenSource source = new CancellationTokenSource();
                CancellationToken cancellationToken = source.Token;
                using var client = new DaprClientBuilder().Build();
                //Using Dapr SDK to invoke a method
                var result = client.CreateInvokeMethodRequest(HttpMethod.Get, "checkout", "checkout/" + orderId, cancellationToken);
                await client.InvokeMethodAsync(result);
                Console.WriteLine("Order requested: " + orderId);
                Console.WriteLine("Result: " + result);
		    }
        }
    }
}

//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{
		while(true) {
			TimeUnit.MILLISECONDS.sleep(5000);
			Random random = new Random();
			int orderId = random.nextInt(1000-1) + 1;
			DaprClient daprClient = new DaprClientBuilder().build();
            //Using Dapr SDK to invoke a method
			var result = daprClient.invokeMethod(
					"checkout",
					"checkout/" + orderId,
					null,
					HttpExtension.GET,
					String.class
			);
			log.info("Order requested: " + orderId);
			log.info("Result: " + result);
		}
	}
}

#dependencies
import random
from time import sleep
import logging
from dapr.clients import DaprClient

#code
logging.basicConfig(level = logging.INFO) 
while True:
    sleep(random.randrange(50, 5000) / 1000)
    orderId = random.randint(1, 1000)
    with DaprClient() as daprClient:
        #Using Dapr SDK to invoke a method
        result = daprClient.invoke_method(
            "checkout",
               f"checkout/{orderId}",
               data=b'',
               http_verb="GET"
        )    
    logging.basicConfig(level = logging.INFO)
    logging.info('Order requested: ' + str(orderId))
    logging.info('Result: ' + str(result))

//dependencies
import (
	"context"
	"log"
	"math/rand"
	"time"
	"strconv"
	dapr "github.com/dapr/go-sdk/client"

)

//code
type Order struct {
	orderName string
	orderNum  string
}

func main() {
	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 a method
		result, err := client.InvokeMethod(ctx, "checkout", "checkout/" + strconv.Itoa(orderId), "get")
		log.Println("Order requested: " + strconv.Itoa(orderId))
		log.Println("Result: ")
		log.Println(result)
	}
}

//dependencies
import { DaprClient, HttpMethod, CommunicationProtocolEnum } from 'dapr-client'; 

//code
const daprHost = "127.0.0.1"; 

var main = function() {
    for(var i=0;i<10;i++) {
        sleep(5000);
        var orderId = Math.floor(Math.random() * (1000 - 1) + 1);
        start(orderId).catch((e) => {
            console.error(e);
            process.exit(1);
        });
    }
}

async function start(orderId) {
    const client = new DaprClient(daprHost, process.env.DAPR_HTTP_PORT, CommunicationProtocolEnum.HTTP);
    //Using Dapr SDK to invoke a method
    const result = await client.invoker.invoke('checkoutservice' , "checkout/" + orderId , HttpMethod.GET);
    console.log("Order requested: " + orderId);
    console.log("Result: " + result);
}

function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

main();

Additional URL formats

To invoke a ‘GET’ endpoint:

curl http://localhost:3602/v1.0/invoke/checkout/method/checkout/100

In order to avoid changing URL paths as much as possible, Dapr provides the following ways to call the service invocation API:

  1. Change the address in the URL to localhost:<dapr-http-port>.
  2. Add a dapr-app-id header to specify the ID of the target service, or alternatively pass the ID via HTTP Basic Auth: http://dapr-app-id:<service-id>@localhost:3602/path.

For example, the following command

curl http://localhost:3602/v1.0/invoke/checkout/method/checkout/100

is equivalent to:

curl -H 'dapr-app-id: checkout' 'http://localhost:3602/checkout/100' -X POST

or:

curl 'http://dapr-app-id:checkout@localhost:3602/checkout/100' -X POST

Using CLI:

dapr invoke --app-id checkout --method checkout/100

Namespaces

When running on namespace supported platforms, you include the namespace of the target app in the app ID: checkout.production

For example, invoking the example service with a namespace would be:

curl http://localhost:3602/v1.0/invoke/checkout.production/method/checkout/100 -X POST

See the Cross namespace API spec for more information on namespaces.

Step 3: View traces and logs

The example above showed you how to directly invoke a different service running locally or in Kubernetes. Dapr outputs metrics, tracing and logging information allowing you to visualize a call graph between services, log errors and optionally log the payload body.

For more information on tracing and logs see the observability article.


Last modified July 26, 2022: Update translations for v1.6 (#2665) (e18b8c6)