java-operator-sdk-readme.md

Build Kubernetes Operators in Java without hassle. Inspired by operator-sdk.

Features

• Framework for handling Kubernetes API events
• Registering Custom Resource watches
• Retry action on failure
• Smart event scheduling (only handle latest event for the same resource)

Check out this blog post about the non-trivial yet common problems needs to be solved for every operator.

Why build your own Operator?

• Infrastructure automation using the power and flexibility of Java. See blog post.
• Provisioning of complex applications - avoiding Helm chart hell
• Integration with Cloud services - e.g. Secret stores
• Safer deployment of applications - only expose cluster to users by Custom Resources

Roadmap

• Testing of the framework and all samples while running on a real cluster.
• Generate a project skeleton
• Generate Java classes from CRD definion (and/or the other way around)
• Integrate with Quarkus (including native image build)
• Integrate with OLM (Operator Lifecycle Manager)

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User Guide

You can (will) find detailed documentation here. Note that these docs are currently in progress.

Usage

We have several sample Operators under the samples directory:

• basic: Minimal Operator implementation which only parses the Custom Resource and prints to stdout. Implemented with and without Spring Boot support. The two samples share the common module.
• webserver: More realistic example creating an nginx webserver from a Custom Resource containing html code.
• mysql-schema: Operator managing schemas in a MySQL database
• spring-boot-plain/auto-config: Samples showing integration with Spring Boot.

Add dependency to your project:

<dependency>
  <groupId>com.github.containersolutions</groupId>
  <artifactId>operator-framework</artifactId>
  <version>{see https://search.maven.org/search?q=a:operator-framework for latest version}</version>
</dependency>

Main method initializing the Operator and registering a controller..

public class Runner {

   public static void main(String[] args) {
       Operator operator = new Operator(new DefaultKubernetesClient());
       operator.registerController(new WebServerController());
   }
}

The Controller implements the business logic and describes all the classes needed to handle the CRD.

@Controller(customResourceClass = WebServer.class,
        crdName = "webservers.sample.javaoperatorsdk")
public class WebServerController implements ResourceController<WebServer> {

    @Override
    public boolean deleteResource(CustomService resource, Context<WebServer> context) {
        // ... your logic ...
        return true;
    }
    
    // Return the changed resource, so it gets updated. See javadoc for details.
    @Override
    public UpdateControl<CustomService> createOrUpdateResource(CustomService resource, Context<WebServer> context) {
        // ... your logic ...
        return UpdateControl.updateStatusSubResource(resource);
    }
}

A sample custom resource POJO representation

public class WebServer extends CustomResource {

    private WebServerSpec spec;

    private WebServerStatus status;

    public WebServerSpec getSpec() {
        return spec;
    }

    public void setSpec(WebServerSpec spec) {
        this.spec = spec;
    }

    public WebServerStatus getStatus() {
        return status;
    }

    public void setStatus(WebServerStatus status) {
        this.status = status;
    }
}

public class WebServerSpec {

    private String html;

    public String getHtml() {
        return html;
    }

    public void setHtml(String html) {
        this.html = html;
    }
}

Spring Boot

You can also let Spring Boot wire your application together and automatically register the controllers.

Add this dependency to your project:

<dependency>
 <groupId>com.github.containersolutions</groupId>
 <artifactId>spring-boot-operator-framework-starter</artifactId>
 <version>{see https://search.maven.org/search?q=a:spring-boot-operator-framework-starter for latest version}</version>
</dependency>

Create an Application

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}