SE This Week: Using etcd as Kubernetes App Database

About

This tutorial will show you how to build a web application using etcd as NoSQL database.

What is etcd?

etcd is a distributed reliable key-value store for the most critical data of a distributed system. etcd is written in Go. Since it is using grpc for user-facing API implementation, that explains why we choose protobuf in our web application.
If you are familiar with Kubernetes, you should know that etcd is a well-known implementation of Kubernetes object storage. That is actually how etcd caught my attention.

Build an etcd web app.

Ok. Let's see how to build a web application using etcd, spring boot and protobuf.

Use spring initializr to create a sample web project (add web dependency in).
Add protobuf plugin and dependency, and etcd java client.

            <plugin>
                <groupId>org.xolstice.maven.plugins</groupId>
                <artifactId>protobuf-maven-plugin</artifactId>
                <version>0.6.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                            <goal>test-compile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

         <dependency>
            <groupId>io.etcd</groupId>
            <artifactId>jetcd-core</artifactId>
            <version>${jetcd-version}</version>
        </dependency>
        <dependency>
            <groupId>com.google.protobuf</groupId>
            <artifactId>protobuf-java</artifactId>
            <version>3.4.0</version>
        </dependency>

Create a protobuf file for communication between etcd and app. It is like schema in SQL world, json in MongoDB world.

syntax = "proto2";
package com.example.proto.model;

option optimize_for = SPEED;

message DemoMessage {
  optional string name = 1;
  optional string body = 2;
}

Let's create an etcd initialization class, which will help you create the connection between the web app and etcd.

@Component
public class DbInitializer {
    @Value("${etcd.url}")
    String etcdUrl;

    public KV initDB() {
        Client client = Client.builder().endpoints(etcdUrl)
                .build();
        KV kvClient = client.getKVClient();
        return kvClient;
    }
}

Now, let's create a dao layer.

@Repository
public class MessageDaoImpl implements MessageDao{

    private KV kvClient;

    public MessageDaoImpl(@Autowired DbInitializer initializer) {
        kvClient = initializer.initDB();
    }

    @Override
    public Message.DemoMessage get(String key) throws ExecutionException, InterruptedException, InvalidProtocolBufferException {
        ByteSequence keySeq = ByteSequence.from(key.getBytes());
        CompletableFuture<GetResponse> getFuture = kvClient.get(keySeq);
        GetResponse response = getFuture.get();
        byte[] data = response.getKvs().get(0).getValue().getBytes();

        return Message.DemoMessage.parseFrom(data);
    }

    @Override
    public void delete(String key) throws ExecutionException, InterruptedException {
        ByteSequence keySeq = ByteSequence.from(key.getBytes());
        kvClient.delete(keySeq).get();

    }

    @Override
    public void add(String key, Message.DemoMessage demoMessage) throws ExecutionException, InterruptedException {
        ByteSequence keySeq = ByteSequence.from(key.getBytes());
        ByteSequence value = ByteSequence.from(demoMessage.toByteArray());
        kvClient.put(keySeq, value).get();
    }

    @Override
    public void update(String key, Message.DemoMessage demoMessage) throws ExecutionException, InterruptedException {
        ByteSequence keySeq = ByteSequence.from(key.getBytes());
        ByteSequence value = ByteSequence.from(demoMessage.toByteArray());
        kvClient.put(keySeq, value).get();
    }
}

Once you have the dao layer, it shouldn't make any difference like how you create a web application. Please refer to this GitHub repo for the completed source code.

How to deploy it to a Kubernetes cluster?

I will use minikube for this tutorial. It shouldn't make any difference if you choose other Kubernetes cluster, like EKS, AKS, GKS.

Start minikube.
minikube start
If you don't have minikube yet, follow this guide.
Deploy etcd.
Download the etcd yaml file from here. And then, run kubectl apply -f etcd.yaml
Deploy our web application.
Download the deployment yaml file from here. And then, run kubectl apply -f deployment.yaml
So far, you should be all good. But, let's expose the web application, so we can test it in our browser. Run this command. minikube service etcd-service

Test

Now, we are ready to test our web application. The previous step should give you a host IP address. Please replace the IP address below with what you get. You call choose postman or any other rest API client to run the CURLs.

Add record
curl -X PUT \
  'http://192.168.99.102:32001/message/1?name=jguo&body=I%20am%20a%20software%20engineer' \
  -H 'cache-control: no-cache'

Get Record
curl -X GET \
  http://192.168.99.102:32001/message/1 \
  -H 'cache-control: no-cache'

Update Record
curl -X POST \
  'http://192.168.99.102:32001/message/1?name=jiayan' \
  -H 'cache-control: no-cache'

Delete Record
curl -X DELETE \
  http://192.168.99.102:32001/message/1 \
  -H 'cache-control: no-cache'

Wrap Up

If you are using Kubernetes to run your web applications and looking for a containerized NoSQL DB, take etcd into your account. The purpose of this post is not to persuade you to choose etcd as your solution. Since choosing a DB it usually has a lot of concerns, making a smart decision.

Reference

https://github.com/jiayanguo/etcdapp
https://kubernetes.io/docs/tasks/administer-cluster/configure-upgrade-etcd/
https://github.com/etcd-io/etcd/tree/master/hack/kubernetes-deploy
https://github.com/etcd-io/jetcd

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