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Merge pull request #2 from learnk8s/java
Java
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‎.gitignore

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*.env
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*.dev
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.DS_Store
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.vscode/
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.vscode/
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.idea/
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target/
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*.iml

‎README.md

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You can find examples in the following languages:
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- [Javascript](javascript/README.md)
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- [Java](java/README.md)
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- [Go](go/README.md)

‎java/README.md

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# Templating Kubernetes resources with Java
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In this section you will learn how to use Java and Maven to:
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- create JSON (and YAML) definition for a Kubernetes Pod
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- submit a Pod definition to the cluster with code
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Let's get started.
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## Prerequisites
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To your Maven application you need to add the `io.fabric8:kubernetes-client` dependency inside the `pom.xml` file
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```xml
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<dependency>
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<groupId>io.fabric8</groupId>
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<artifactId>kubernetes-client</artifactId>
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<version>4.6.4</version>
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</dependency>
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```
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## Generating Pod definitions
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The code is short:
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```java
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public static void main(String[] args) throws Exception {
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String environment = "production";
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Pod pod = createPod(namespace);
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if (args[0].equals("yaml")) {
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System.out.println(SerializationUtils.dumpAsYaml(pod));
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} else {
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System.out.println(mapper.writeValueAsString(pod));
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}
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}
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public static Pod createPod( String environment ) {
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return new PodBuilder().withNewMetadata()
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.withName("test-pod")
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.endMetadata()
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.withNewSpec()
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.addNewContainer()
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.withName("test-container")
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.withImage("k8s.gcr.io/busybox")
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.withEnv(new EnvVarBuilder().withName("ENV").withValue(environment).build())
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.endContainer()
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.endSpec()
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.build();
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}
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```
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You can compile and package the Maven application with:
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```shell
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mvn clean package
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```
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You can execute the the application with:
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```shell
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java -jar target/k8s-client-1.0.jar --dry-run
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```
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The output is a JSON object for the Pod.
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```json
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{
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"apiVersion" : "v1",
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"kind" : "Pod",
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"metadata" : {
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"annotations" : { },
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"labels" : { },
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"name" : "test-pod"
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},
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"spec" : {
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"containers" : [ {
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"env" : [ {
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"name" : "ENV",
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"value" : "production"
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} ],
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"image" : "k8s.gcr.io/busybox",
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"name" : "test-container"
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} ],
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"nodeSelector" : { }
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}
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}
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```
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_But isn't Kubernetes accepting only YAML?_
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YAML is a superset of JSON and any JSON file is also a valid YAML file.
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You can create the Pod in the cluster with the following commands:
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```shell
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java -jar target/k8s-client-1.0.jar yaml --dry-run
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kubectl apply -f pod.yaml
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```
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## Creating a custom Kubectl
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Instead of exporting the JSON and feeding it to kubectl, you can send the payload to the cluster directly.
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You can use the [Fabric8 Kubernetes API](https://github.com/fabric8io/kubernetes-client) to send the Pod definition to the cluster.
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Here's the code:
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```java
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Config config = new ConfigBuilder().build();
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try (final KubernetesClient client = new DefaultKubernetesClient(config)) {
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if (namespace == null) {
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namespace = client.getNamespace();
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}
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boolean dryRun = false;
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for (String arg : args) {
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if (arg.equals("--dry-run")) {
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dryRun = true;
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}
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}
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if (!dryRun) {
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client.pods().inNamespace(namespace).create(pod);
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System.out.println("Pod created!");
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}
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}
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```
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Assuming you are connected to a running cluster, you can execute the script with:
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```shell
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java -jar target/k8s-client-1.0.jar yaml
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```
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And you can verify that the Pod was created with:
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```shell
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kubectl get pods
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```
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## What's next
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As you can imagine, this is a short demo and you can build more complex objects and use the power of Java and the Fabric8 Kubernetes API to compose large objects from smaller ones.

‎java/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>io.learnk8s</groupId>
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<artifactId>k8s-client</artifactId>
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<version>1.0</version>
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<name>k8s-client</name>
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<properties>
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<java.version>11</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>io.fabric8</groupId>
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<artifactId>kubernetes-client</artifactId>
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<version>4.6.4</version>
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</dependency>
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<dependency>
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<groupId>org.slf4j</groupId>
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<artifactId>slf4j-api</artifactId>
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<version>1.7.25</version>
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</dependency>
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<dependency>
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<groupId>org.slf4j</groupId>
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<artifactId>slf4j-jdk14</artifactId>
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<version>1.7.25</version>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-compiler-plugin</artifactId>
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<configuration>
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<source>11</source>
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<target>11</target>
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</configuration>
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</plugin>
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<plugin>
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<artifactId>maven-assembly-plugin</artifactId>
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<executions>
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<execution>
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<phase>package</phase>
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<goals>
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<goal>single</goal>
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</goals>
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</execution>
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</executions>
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<configuration>
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<archive>
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<manifest>
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<addClasspath>true</addClasspath>
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<mainClass>io.learnk8s.KubernetesClientCLI</mainClass>
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</manifest>
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</archive>
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<descriptorRefs>
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<descriptorRef>jar-with-dependencies</descriptorRef>
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</descriptorRefs>
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<finalName>${project.name}-${project.version}</finalName>
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<appendAssemblyId>false</appendAssemblyId>
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</configuration>
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</plugin>
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</plugins>
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</build>
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</project>

‎java/src/main/java/io/learnk8s/KubernetesClientCLI.java

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package io.learnk8s;
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import com.fasterxml.jackson.databind.ObjectMapper;
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import com.fasterxml.jackson.databind.SerializationFeature;
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import io.fabric8.kubernetes.api.model.*;
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import io.fabric8.kubernetes.client.*;
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import io.fabric8.kubernetes.client.Config;
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import io.fabric8.kubernetes.client.ConfigBuilder;
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import io.fabric8.kubernetes.client.internal.SerializationUtils;
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public class KubernetesClientCLI {
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private static final ObjectMapper mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);
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private static String namespace = null;
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public static void main(String[] args) throws Exception {
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String environment = "production";
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Pod pod = createPod(environment);
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if (args.length > 0 && args[0].equals("yaml")) {
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System.out.println(SerializationUtils.dumpAsYaml(pod));
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} else {
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System.out.println(mapper.writeValueAsString(pod));
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}
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Config config = new ConfigBuilder().build();
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try (final KubernetesClient client = new DefaultKubernetesClient(config)) {
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if (namespace == null) {
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namespace = client.getNamespace();
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}
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boolean dryRun = false;
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for (String arg : args) {
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if (arg.equals("--dry-run")) {
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dryRun = true;
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}
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}
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if (!dryRun) {
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client.pods().inNamespace(namespace).create(pod);
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System.out.println("Pod created!");
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}
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}
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}
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public static Pod createPod(String environment){
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return new PodBuilder().withNewMetadata()
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.withName("test-pod")
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.endMetadata()
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.withNewSpec()
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.addNewContainer()
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.withName("test-container")
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.withImage("k8s.gcr.io/busybox")
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.withEnv(new EnvVarBuilder().withName("ENV").withValue(environment).build())
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.endContainer()
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.endSpec()
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.build();
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}
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}

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