Tomcat Operator

Tomcat Operator sample project for the Java Operator SDK.

Description

This is a sample project that shows how to use the Java Operator SDK to create an operator that manages Tomcat webservers and deploy war files in them. The operator will create a Deployment and a Service for each Tomcat instance. The Tomcat version and the number of replicas can be configured in the Tomcat Custom Resource. The operator will download and deploy a war file to the target Tomcat instance for each Webapp Custom Resource that is created. The Webapp resource contains the URL to the WAR file and the context path to deploy the WAR file to.

This sample demonstrates the following capabilities of the Java Operator SDK:

• Multiple Controllers in a single Operator. The Tomcat resource is managed by the TomcatController while the Webapp resource is managed by the WebappController.
• Reacting to events about resources created by the controller. The TomcatController will receive events about the Deployment resources it created. See EventSource section below for more detail.

Example input for creating a Tomcat instance

apiVersion: "tomcatoperator.io/v1"
kind: Tomcat
metadata:
  name: test-tomcat1
spec:
  version: 9.0
  replicas: 2

Example input for the Webapp

apiVersion: "tomcatoperator.io/v1"
kind: Webapp
metadata:
  name: sample-webapp1
spec:
  tomcat: test-tomcat1
  url: http://tomcat.apache.org/tomcat-7.0-doc/appdev/sample/sample.war
  contextPath: mysample

Getting started / Testing

The quickest way to try the operator is to run it on your local machine, while it connects to a local or remote Kubernetes cluster. When you start it, it will use the current kubectl context on your machine to connect to the cluster.

Before you run it you have to install the CRDs on your cluster by running:

• kubectl apply -f target/classes/META-INF/fabric8/tomcats.tomcatoperator.io-v1.yml
• kubectl apply -f target/classes/META-INF/fabric8/webapps.tomcatoperator.io-v1.yml

The CRDs are generated automatically from your code by simply adding the crd-generator-apt dependency to your pom.xml file.

When the Operator is running you can create some Tomcat Custom Resources. You can find a sample custom resources in the k8s folder.

If you want the Operator to be running as a deployment in your cluster, follow the below steps.

Build

You can build the sample using mvn install jib:dockerBuild this will produce a Docker image you can push to the registry of your choice. The JAR file is built using your local Maven and JDK and then copied into the Docker image.

Install Operator into cluster

Install the CRDs as shown above if you haven't already, then run kubectl apply -f k8s/operator.yaml. Now you can create Tomcat instances with CRs (see examples above).

EventSources

The TomcatController is listening to events about Deployments created by the TomcatOperator by registering a InformerEventSource with the EventSourceManager. The InformerEventSource will in turn register a watch on all Deployments managed by the Controller (identified by the app.kubernetes.io/managed-by label). When an event from a Deployment is received we have to identify which Tomcat object does the Deployment belong to. This is done when the InformerEventSource creates the event.

The TomcatController has to take care of setting the app.kubernetes.io/managed-by label on the Deployment so the InformerEventSource can watch the right Deployments. The TomcatController also has to set ownerReference on the Deployment so later the InformerEventSource can identify which Tomcat does the Deployment belong to. This is necessary so the framework can call the Controller reconcile method correctly.