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Using Kubernetes ConfigMaps to define your Quarkus application’s properties - xSicKxBot - 03-27-2022
Using Kubernetes ConfigMaps to define your Quarkus application’s properties
<div style="margin: 5px 5% 10px 5%;"><img src="https://www.sickgaming.net/blog/wp-content/uploads/2020/01/using-kubernetes-configmaps-to-define-your-quarkus-applications-properties.png" width="16" height="16" title="" alt="" /></div><div><p>So, you wrote your Quarkus application, and now you want to deploy it to a Kubernetes cluster. Good news: Deploying a Quarkus application to a Kubernetes cluster is easy. Before you do this, though, you need to straighten out your application’s properties. After all, your app probably has to connect with a database, call other services, and so on. These settings are already defined in your <code>application.properties</code> file, but the values match the ones for your local environment and won’t work once deployed onto your cluster.</p>
<p>So, how do you easily solve this problem? Let’s walk through an example.</p>
<p><span id="more-675247"></span></p>
<h2>Create the example Quarkus application</h2>
<p>Instead of using a complex example, let’s take a simple use case that explains the concept well. Start by creating a new Quarkus app:</p>
<pre>$ mvn io.quarkus:quarkus-maven-plugin:1.1.1.Final:create</pre>
<p>You can keep all of the default values while creating the new application. In this example, the application is named <code>hello-app</code>. Now, open the <code>HelloResource.java</code> file and refactor it to look like this:</p>
<pre>@Path("/hello") public class HelloResource { @ConfigProperty(name = "greeting.message") String message; @GET @Produces(MediaType.TEXT_PLAIN) public String hello() { return "hello " + message; } } </pre>
<p>In your <code>application.properties</code> file, now add <code>greeting.message=localhost</code>. The <code>@ConfigProperty</code> annotation is not in the scope of this article, but here we can see how easy it is to inject properties inside our code using this annotation.</p>
<p>Now, let’s start our application to see if it works as expected: <code></code></p>
<pre>$ mvn compile quarkus:dev</pre>
<p>Browse to <code>http://localhost:8080/hello</code>, which should output <code>hello localhost</code>. That’s it for the Quarkus app. It’s ready to go.</p>
<h2>Deploy the application to the Kubernetes cluster</h2>
<p>The idea here is to deploy this application to our Kubernetes cluster and replace the value of our <code>greeting</code> property with one that will work on the cluster. It is important to know here that all of the properties from <code>application.properties</code> are exposed, and thus can be overridden with environment variables. The convention is to convert the name of the property to uppercase and replace every dot (<code>.</code>) with an underscore (<code>_</code>). So, for instance, our <code>greeting.message</code> will become <code>GREETING_MESSAGE</code>.</p>
<p>At this point, we are almost ready to deploy our app to Kubernetes, but we need to do three more things:</p>
<ol>
<li>Create a Docker image of your application and push it to a repository that your cluster can access.</li>
<li>Define a ConfgMap resource.</li>
<li>Generate the Kubernetes resources for our application.</li>
</ol>
<p>To create the Docker image, simply execute this command:</p>
<pre>$ docker build -f src/main/docker/Dockerfile.jvm -t quarkus/hello-app .</pre>
<p>Be sure to set the right Docker username and to also push to an image registry, like <code>docker-hub</code> or <code>quay</code>. If you are not able to push an image, you can use <code>sebi2706/hello-app:latest</code>.</p>
<p>Next, create the file <code>config-hello.yml</code>:</p>
<pre>apiVersion: v1 data: greeting: "Kubernetes" kind: ConfigMap metadata: name: hello-config </pre>
<p>Make sure that you are connected to a cluster and apply this file:</p>
<pre>$ kubectl apply -f config-hello.yml</pre>
<p>Quarkus comes with a useful extension, <code>quarkus-kubernetes</code>, that generates the Kubernetes resources for you. You can even tweak the generated resources by providing extra properties—for more details, check out this <a href="https://quarkus.io/guides/kubernetes" target="_blank" rel="noopener noreferrer">guide</a>.</p>
<p>After installing the extension, add these properties to our <code>application.properties</code> file so it generates extra configuration arguments for our containers specification:</p>
<pre>kubernetes.group=yourDockerUsername kubernetes.env-vars[0].name=GREETING_MESSAGE kubernetes.env-vars[0].value=greeting kubernetes.env-vars[0].configmap=hello-config</pre>
<p>Run <code>mvn package</code> and view the generated resources in <code>target/kubernetes</code>. The interesting part is in <code>spec.containers.env</code>:</p>
<pre>- name: "GREETING_MESSAGE" valueFrom: configMapKeyRef: key: "greeting" name: "hello-config"</pre>
<p>Here, we see how to pass an environment variable to our container with a value coming from a ConfigMap. Now, simply apply the resources:</p>
<pre>$ kubectl apply -f target/kubernetes/kubernetes.yml</pre>
<p>Expose your service:</p>
<pre class="highlightjs highlight"><code class="language-shell hljs" data-lang="shell">kubectl expose deployment hello --type=NodePort</code></pre>
<p>Then, browse to the public URL or do a curl. For instance, with Minikube:</p>
<pre class="highlightjs highlight"><code class="language-shell hljs" data-lang="shell">$ curl $(minikube service hello-app --url)/hello</code></pre>
<p>This command should output: <code>hello Kubernetes</code>.</p>
<h2>Conclusion</h2>
<p>Now you know how to use a ConfigMap in combination with environment variables and your Quarkus’s <code>application.properties</code>. As we said in the introduction, this technique is particularly useful when defining a DB connection’s URL (like <code>QUARKUS_DATASOURCE_URL</code>) or when using the <code>quarkus-rest-client</code> (<code>ORG_SEBI_OTHERSERVICE_MP_REST_URL</code>).</p>
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<p>The post <a rel="nofollow" href="https://developers.redhat.com/blog/2020/01/23/using-kubernetes-configmaps-to-define-your-quarkus-applications-properties/">Using Kubernetes ConfigMaps to define your Quarkus application’s properties</a> appeared first on <a rel="nofollow" href="https://developers.redhat.com/blog">Red Hat Developer</a>.</p>
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