3-GoLangAppOnDAPR.md

Writing Simple GoLang App/Program using DAPR

( Distributed APplication Runtime )

Basic DAPR Terminology

• Dapr CLI is a cross-platform command-line tool that you can use to configure, manage, and monitor your Dapr instances. It also provides access to useful tools such as the Dapr dashboard.

• Dapr host hosts an instance of the Dapr runtime. The most common form is a Docker container, which is injected into a pod to run side by side with user code on Kubernetes.4 Dapr can also run in standalone mode as a service process or a daemon, it implements communication protocols such as HTTP and gRPC.

• Dapr API defines the programmable interface to the Dapr runtime.5

• Dapr runtime implements the Dapr API. It’s the core of Dapr’s functionality.

• Dapr operator is a Kubernetes-specific component that supports Dapr’s Kubernetes mode. It manages configurations and bindings, which are implemented as Kubernetes custom resources.

• Dapr sidecar injector handles Dapr sidecar container injection when Dapr runs in Kubernetes mode.

There are few more DAPR terms and concepts which we will understand in more advance topics.

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Lets start Hands-On

You can use DAPR in self hosted mode or on your Kubernetes cluster, In this exercise we will focus mainly on Self Hosted Mode

1. Uninstall DAPR if you want fresh start (although not mandatory)

dapr uninstall

or if you want to uninstall from your Kubernetes cluster

dapr uninstall -k

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2. Init DAPR

dapr init

or if you want to install it to your kubernetes cluster

dapr init -k

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3. Check the status of Dapr

dapr status

or if you want to see the status of DAPR on your K8s cluster

dapr init -k

4. Get List of Containers running by DAPR

docker ps

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5. Write a Simple GoLang Program to do following
   • a) Welcome Message at path /
   • b) Greeting Message at path /greeting
   • c) Greeting by name at path /greetme?name=[YourName]

Create file main.go and write following code

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"time"
)

type incomingEvent struct {
	Data interface{} `json:"data"`
}

func main() {

	http.HandleFunc("/",
		func(w http.ResponseWriter, r *http.Request) {
			fmt.Fprintf(w, "Welcome to first GoLang Web Program running using DAPR! "+time.Now().Format("2006-01-02 15:04:05")) //YYYY-MM-DD hh:mm:ss
		})

	http.HandleFunc("/greeting",
		func(w http.ResponseWriter, r *http.Request) {
			var event incomingEvent
			decoder := json.NewDecoder(r.Body)
			decoder.Decode(&event)
			fmt.Println(event.Data)
			fmt.Fprintf(w, "Welcome, Greetings of the day from DAPR !! "+time.Now().Format("2006-01-02 15:04:05"))
		})

	http.HandleFunc("/greetme",
		func(w http.ResponseWriter, r *http.Request) {
			var event incomingEvent
			decoder := json.NewDecoder(r.Body)
			decoder.Decode(&event)
			fmt.Println(event.Data)

			keys, ok := r.URL.Query()["name"]
			if !ok || len(keys[0]) < 1 {
				log.Println("Url Param 'name' is missing")
				return
			}
			// Query()["key"] will return an array of items,
			// we only want the single item.
			name := keys[0]

			fmt.Fprintf(w, "Welcome "+string(name)+", Greetings of the day from DAPR !! "+time.Now().Format("2006-01-02 15:04:05"))
		})

	log.Fatal(http.ListenAndServe(":8080", nil))
}

You can also refer the source code inside src/GoLangSamples/BasicSample folder of this repo

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6. Now from the same location where main.go is present , run following command

dapr run --app-id dapr-greetings --app-port 8080 --port 8089 go run main.go

You will see the output as shown below (notice the highlighted command) inside VSCode Integrated Terminal, here we have given the name of our app as dapr-greetings and we are running it at port 8088 , while the port of Dapr Sidecar process is 8089

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7. Open your favorite browser and try the three endpoints below

   • a) Welcome Message at path /
   
   • b) Greeting Message at path /greeting
   
   • c) Greeting by name at path /greetme?name=[YourName]
   

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8. Finally you can see list of DAPR apps running

dapr list

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9. You can also run DAPR Dashboard for monitoring (Learn more about DAPR Dashboard here https://github.com/dapr/dashboard )

dapr dashboard

Now Open http://localhost:8080 to see DAPR Dashboard