This quickstart shows method invocation and state persistent capabilities of Dapr through a distributed calculator where each operation is powered by a different service written in a different language/framework:
- Addition: Go mux application
- Multiplication: Python flask application
- Division: Node Express application
- Subtraction: .NET Core application
The front-end application consists of a server and a client written in React. Kudos to ahfarmer whose React calculator
The following architecture diagram illustrates the components that make up this quickstart:
Clone the quickstarts repository
git clone [-b <dapr_version_tag>] https://github.com/dapr/quickstarts.gitNote: See https://github.com/dapr/quickstarts#supported-dapr-runtime-version for supported tags. Use
git clone https://github.com/dapr/quickstarts.gitwhen using the edge version of dapr runtime.
- Dapr-enabled Kubernetes cluster. Follow these instructions to set this up.
These instructions start the four calculator operator apps (add, subtract, multiply and divide) along with the dapr sidecar locally and then run the front end app which persists the state in a local redis state store.
- Add App - Open a terminal window and navigate to the go directory and follow the steps below:
- Install the gorilla/mux package: Run:
go get -u github.com/gorilla/mux
- Build the app. Run:
go build .
- Run dapr using the command:
dapr run --app-id addapp --app-port 6000 --dapr-http-port 3503 go run app.go
- Subtract App - Open a terminal window and navigate to the csharp directory and follow the steps below:
-
Set environment variable to use non-default app port 7001
#Linux/Mac OS: export ASPNETCORE_URLS="http://localhost:7001"
#Windows: set ASPNETCORE_URLS=http://localhost:7001
- Build the app. Run:
dotnet build
- Navigate to ./bin/Debug/netcoreapp3.1 and start Dapr using command:
dapr run --app-id subtractapp --app-port 7001 --dapr-http-port 3504 dotnet Subtract.dll
- Divide App - Open a terminal window and navigate to the node directory and follow the steps below:
- Install dependencies by running the command:
npm install
- Start Dapr using the command below
dapr run --app-id divideapp --app-port 4000 --dapr-http-port 3502 node app.js
- Multiply App - Open a terminal window and navigate to the python directory and follow the steps below:
- Install required packages
pip3 install wheel python-dotenv flask_cors flask
- Set environment variable to use non-default app port 5000
#Linux/Mac OS: export FLASK_RUN_PORT=5001 #Windows: set FLASK_RUN_PORT=5001
- Start dapr using the command:
dapr run --app-id multiplyapp --app-port 5001 --dapr-http-port 3501 flask run
- Frontend Calculator app - Open a terminal window and navigate to the react-calculator directory and follow the steps below:
- Install the required modules
npm install npm run buildclient
- Start Dapr using command below:
dapr run --app-id frontendapp --app-port 8080 --dapr-http-port 3507 node server.js
-
Open a browser window and go to http://localhost:8080/. From here, you can enter the different operations.
-
Open your browser's console window (using F12 key) to see the logs produced as you use the calculator. Note that each time you click a button, you see logs that indicate state persistence and the different apps that are contacted to perform the operation.
- Optional: Curl Validate
-
To make sure all the apps are working, you can run the following curl commands which will test all the operations:
curl -s http://localhost:8080/calculate/add -H Content-Type:application/json --data @operands.json
curl -s http://localhost:8080/calculate/subtract -H Content-Type:application/json --data @operands.json
curl -s http://localhost:8080/calculate/divide -H Content-Type:application/json --data @operands.json
curl -s http://localhost:8080/calculate/multiply -H Content-Type:application/json --data @operands.json
curl -s http://localhost:8080/persist -H Content-Type:application/json --data @persist.json
curl -s http://localhost:8080/state
- You should get the following output:
86 18 1.5294117647058822 1768 {"operation":null,"total":"54","next":null}
- Cleanup
-
Cleanup microservices
dapr stop --app-id addapp
dapr stop --app-id subtractapp
dapr stop --app-id divideapp
dapr stop --app-id multiplyapp
dapr stop --app-id frontendapp
- Uninstall node modules by navigating to the node directory and run:
npm uninstall
- Navigate to the deploy directory in this quickstart directory:
cd deployNote:
appconfig.yamlis not used directly for this quickstart but is present for the observability quickstart. - Follow these instructions to create and configure a Redis store
- Deploy all of your resources:
kubectl apply -f .Note: Services could also be deployed one-by-one by specifying the .yaml file:
kubectl apply -f go-adder.yaml.
Each of the services will spin up a pod with two containers: one for your service and one for the Dapr sidecar. It will also configure a service for each sidecar and an external IP for the front-end, which allows us to connect to it externally.
- Kubernetes deployments are asyncronous. This means you'll need to wait for the deployment to complete before moving on to the next steps. You can do so with the following commands:
kubectl rollout status deploy/addappkubectl rollout status deploy/subtractappkubectl rollout status deploy/divideappkubectl rollout status deploy/multiplyappkubectl rollout status deploy/calculator-front-endYou can view the status of the running pods with:
kubectl get podsWhen everything is running properly, you'll see output like this:
NAME READY STATUS RESTARTS AGE
addapp-5ff9586df6-5bpll 2/2 Running 0 16s
calculator-front-end-56dc959b58-bb8vw 2/2 Running 0 16s
divideapp-c64f744d6-wljcc 2/2 Running 0 16s
multiplyapp-6989454d77-tkd6c 2/2 Running 0 16s
subtractapp-869b74f676-9mw94 2/2 Running 0 16s
- Next, setup access to your service
There are several different ways to access a Kubernetes service depending on which platform you are using. Port forwarding is one consistent way to access a service, whether it is hosted locally or on a cloud Kubernetes provider like AKS.
kubectl port-forward service/calculator-front-end 8000:80This will make your service available on http://localhost:8000. Navigate to this address with your browser and voilà! You have a working distributed calculator!
Optional: If you are using a public cloud provider, you can substitue your EXTERNAL-IP address instead of port forwarding. You can find it with:
kubectl get svcNAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
dapr-api ClusterIP 10.103.71.22 <none> 80/TCP 135m
dapr-placement ClusterIP 10.103.53.127 <none> 80/TCP 135m
dapr-sidecar-injector ClusterIP 10.104.220.35 <none> 443/TCP 135m
addapp-dapr ClusterIP 10.0.1.170 <none> 80/TCP,50001/TCP 2m
calculator-front-end LoadBalancer 10.0.155.131 40.80.152.125 80:32633/TCP 3m
calculator-front-end-dapr ClusterIP 10.0.230.219 <none> 80/TCP,50001/TCP 3m
divideapp-dapr ClusterIP 10.0.240.3 <none> 80/TCP,50001/TCP 1m
kubernetes ClusterIP 10.0.0.1 <none> 443/TCP 33d
multiplyapp-dapr ClusterIP 10.0.217.211 <none> 80/TCP,50001/TCP 1m
subtractapp-dapr ClusterIP 10.0.146.253 <none> 80/TCP,50001/TCP 2mEach service ending in "-dapr" represents your services respective sidecars, while the calculator-front-end service represents the external load balancer for the React calculator front-end.
- Open your browser's console window (using F12 key) to see the logs produced as you use the calculator. Note that each time you click a button, you see logs that indicate state persistence:
Persisting State:
{total: "21", next: "2", operation: "x"}total, next, and operation reflect the three pieces of state a calculator needs to operate. The app persists these to a Redis store (see Simplified State Management section below). By persisting these, you can refresh the page or take down the front-end pod and still jump right back where you were. Try it! Enter something into the calculator and refresh the page. The calculator should have retained the state, and the console should read:
Rehydrating State:
{total: "21", next: "2", operation: "x"}Also note that each time you enter a full equation (e.g. "126 ÷ 3 =") the logs indicate that a call is made to the service:
Calling divide serviceThe client code calls to an Express server, which routes the calls through Dapr to the back-end services. In this case the divide endpoint is called on the nodejs application.
- Optional: If your environment doesn't have easy access to a browser, or you just like using curl
Then you can use the following curl commands to make sure each one of the microservies is working:
curl -s http://localhost:8000/calculate/add -H Content-Type:application/json --data @operands.jsoncurl -s http://localhost:8000/calculate/subtract -H Content-Type:application/json --data @operands.jsoncurl -s http://localhost:8000/calculate/divide -H Content-Type:application/json --data @operands.jsoncurl -s http://localhost:8000/calculate/multiply -H Content-Type:application/json --data @operands.jsoncurl -s http://localhost:8000/persist -H Content-Type:application/json --data @persist.jsoncurl -s http://localhost:8000/state You should get the following output:
86
18
1.5294117647058822
1768
{"operation":null,"total":"54","next":null}- Once you're done, you can spin down your Kubernetes resources by navigating to the
./deploydirectory and running:
kubectl delete -f .This will spin down each resource defined by the .yaml files in the deploy directory, including the state component.
This quickstart demonstrates how to use Dapr as a programming model for simplifying the development of distributed systems. In this quickstart, Dapr is enabling polyglot programming, service discovery and simplified state management.
Each service in this quickstart is written in a different programming language, but they're used together in the same larger application. Dapr itself is language agnostic - none of the services have to include any dependency in order to work with Dapr. This empowers developers to build each service however they want, using the best language for the job or for a particular dev team.
When the front-end server calls the respective operation services (see server.js code below), it doesn't need to know what IP address they live at or how they were built. Instead it calls their local dapr side-car by name, which knows how to invoke the method on the service, taking advantage of the platform’s service discovery mechanism, in this case Kubernetes DNS resolution.
The code below shows calls to the "add" and "subtract" services via the Dapr URLs:
const daprUrl = `http://localhost:${daprPort}/v1.0/invoke`;
app.post('/calculate/add', async (req, res) => {
const appResponse = await axios.post(`${daprUrl}/addapp/method/add`, req.body);
return res.send(`${appResponse.data}`);
});
app.post('/calculate/subtract', async (req, res) => {
const appResponse = await axios.post(`${daprUrl}/subtractapp/method/subtract`, req.body);
return res.send(`${appResponse.data}`);
});
...Microservice applications are dynamic with scaling, updates and failures causing services to change their network endpoints. Dapr enables you to call service endpoints with a consistent URL syntax, utilizing the hosting platform’s service discovery capabilities to resolve the endpoint location.
Learn more about Dapr service invocation.
Dapr sidecars provide state management. In this quickstart, the calculator's state is persisted each time a new button is clicked. This means a user can refresh the page, close the page or even take down the calculator-front-end pod, and still retain the same state when they next open it. Dapr adds a layer of indirection so that the app doesn't need to know where it's persisting state. It doesn't have to keep track of keys, handle retry logic or worry about state provider specific configuration. All it has to do is GET or POST against its Dapr sidecar's state endpoint: http://localhost:3500/v1.0/state/${stateStoreName}.
Take a look at server.js in the react-calculator directory. Note that it exposes two state endpoints for the React client to get and set state: the GET /state endpoint and the POST /persist endpoint. Both forward client calls to the Dapr state endpoint:
const stateUrl = `http://localhost:${daprPort}/v1.0/state/${stateStoreName}`;Our client persists state by simply POSTing JSON key-value pairs (see react-calculator/client/src/component/App.js):
const state = [{
key: "calculatorState",
value
}];
fetch("/persist", {
method: "POST",
body: JSON.stringify(state),
headers: {
"Content-Type": "application/json"
}
});If you are using Visual Studio Code, you can debug this application using the preconfigured launch.json and task.json files in the .vscode folder. The .vscode folder has already been modified in the project to allow users to launch a compound configuration called "Full Dapr App" which will run all applications and allow you to debug in VS Code.
For more information on how to configure the files visit How-To: Debug multiple Dapr applications
Note: You still need to edit your environment variables for Flask and ASPNETCORE_URLS Note: Dapr offers a preview Dapr Visual Studio Code extension for local development which enables users a variety of features related to better managing their Dapr applications and debugging of your Dapr applications for all supported Dapr languages which are .NET, Go, PHP, Python and Java.
- Explore additional quickstarts.