Hello tomcat

A hello world tomcat application to be deployed to Kubernetes.

I am proposing several approaches:

1. Minikube with Dockerfile and YAML files
2. Minikube with JKube
3. Openshift (Red Hat Developer Sandbox) with JKube

Prerequisites

Minikube

You will need the following to run it with Minikube:

• minikube installed and running on your computer

• minikube ingress addon enabled

  $ minikube addons enable ingress
  

Docker or podman

For the Dockerfile/YAML approach, docker or podman is required.

To push to Quay.io

• create an account in https://quay.io

• create a repo quay.io/yourusername/hello-tomcat

• replace in the following, adapt quay.io/sunix/hello-tomcat with quay.io/sunix/hello-tomcat.

• login into quay.io

  $ docker login quay.io
  

With Dockerfiles and YAML files

Dockerfile

Build the war

$ mvn clean install
$ ls target |grep war
hello-tomcat.war

Build the container image

$ docker build -f src/main/docker/Dockerfile -t quay.io/sunix/hello-tomcat .

Before runing the container, notice that there is no tomcat process

$ ps -awx | grep tomcat

Test:

$ docker run -p 8888:8080 quay.io/sunix/hello-tomcat

Try it: http://localhost:8888

Optionally push the container image to the registry

$ docker push quay.io/sunix/hello-tomcat

Notice that there is only one process from inside the container:

$ ps -awx | grep tomcat

should not be empty, show without the grep should see the other process in the system

$ docker ps

CONTAINER ID  IMAGE                              COMMAND          CREATED         STATUS             PORTS                   NAMES
7a02ccc02de9  quay.io/sunix/hello-tomcat:latest  catalina.sh run  25 seconds ago  Up 25 seconds ago  0.0.0.0:8888->8080/tcp  funny_elbakyan

$ docker exec -it 7a02ccc02de9 bash
root@7a02ccc02de9:/usr/local/tomcat# ps -awx
    PID TTY      STAT   TIME COMMAND
      1 ?        Ssl    0:03 /usr/local/openjdk-11/bin/java -Djava.util.logging.config.file=/usr/local/tomcat/conf/logging.properties -D
     48 pts/0    Ss     0:00 bash
     50 pts/0    R+     0:00 ps -awx

It is big distributed YAML database

Create a namespace and switch to it:

$ kubectl create namespace demo

$ kubectl config set-context --current --namespace=demo

Look at this "CRD" it is like a database schema !

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  # name must match the spec fields below, and be in the form: <plural>.<group>
  name: helloresources.stable.world.com
spec:
  group: stable.world.com
  scope: Namespaced
  names:
    plural: helloresources
    singular: helloresource
    kind: HelloResource
    shortNames:
    - hr
  versions:
    - name: v1
      # Each version can be enabled/disabled by Served flag.
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                hello:
                  type: string

If you try to get the helloresource resources

$ kubectl get helloresource
error: the server doesn't have a resource type "helloresource"

You have to register the type/kind and its schema

$ kubectl apply -f hello-resource.yaml
customresourcedefinition.apiextensions.k8s.io/helloresources.stable.world.com created
$ kubectl get helloresource
No resources found in demo namespace.

and you can create a new hello resource:

$ cat <<EOF | kubectl apply -f -
apiVersion: "stable.world.com/v1"
kind: HelloResource
metadata:
  name: hello-world
spec:
  hello: "world"
EOF

helloresource.stable.world.com/hello-world created

$ kubectl get helloresource -o jsonpath='{range .items[*]}{.metadata.name} hello: {.spec.hello}{"\n"}{end}'

YAML

Update the docker image in kubernetes.yaml file.

To deploy in Minikube:

$ kubectl apply -f kubernetes.yaml

Get the URL

$ minikube service hellotomcat-service --url -n demo

Ingress

Problem with nodeport is that

• either you specify a port... but what if it conflicts?
• you let it choose for you ... but it's random

Let's use the ingress which is the most advanced way to expose a service

Excellent blog post for the difference between nodeport,loadbalancer and ingress: https://medium.com/google-cloud/kubernetes-nodeport-vs-loadbalancer-vs-ingress-when-should-i-use-what-922f010849e0

Replace in ingress.yaml the host with the result of

$ echo $(minikube ip).nip.io

Apply

$ kubectl apply -f ingress.yaml # DON'T FORGET TO INSTALL THE INGRESS MINIKUBE ADDON !!!!
$ kubectl get ingress
NAME                  CLASS    HOSTS                   ADDRESS          PORTS   AGE
hellotomcat-ingress   <none>   192.168.99.116.nip.io   192.168.99.116   80      16s

Try it with the host URL.

Scale

update replicas to 5 in kubernetes.yaml

$ kubectl apply -f kubernetes.yaml

observe the creation and deployment of the 5 pods

$ kubectl get pods

Clean up

$ kubectl delete ingress hellotomcat-ingress
$ kubectl delete service hellotomcat-service
$ kubectl delete deployment hellotomcat

Other useful commands

To force redeployment (for instance if you have rebuilt the container image):

$ kubectl replace --force -f kubernetes.yaml

With JKube

With JKube it is a lot simpler: just add a plugin in pom.xml

Prerequisites

We will use the docker daemon installed in the minikube

$ eval $(minikube -p minikube docker-env)

or if you use podman

$ eval $(minikube -p minikube podman-env)

Adding the JKube plugin

In pom.xml add in the build section:

<plugins>
  <plugin>
    <groupId>org.eclipse.jkube</groupId>
    <artifactId>kubernetes-maven-plugin</artifactId>
    <version>1.10.0</version>
  </plugin>
</plugins>

and just run

$ mvn clean install k8s:build k8s:resource k8s:apply

Ingress

To also create an ingress: In pom.xml properties section:

<jkube.createExternalUrls>true</jkube.createExternalUrls>

We still have to specify the domain to be used:

$ mvn k8s:resource -Djkube.domain=$(minikube ip).nip.io k8s:apply

Scale

Add to pom.xml

<jkube.replicas>10</jkube.replicas>

Give it a try:

$ mvn k8s:resource -Djkube.domain=$(minikube ip).nip.io k8s:apply

Clean up

$ mvn k8s:undeploy

The Red Hat Developer Sandbox

Prerequisites

• Create an account here: https://developers.redhat.com/developer-sandbox/get-started
• Install oc
• Login with oc see https://developers.redhat.com/blog/2021/04/21/access-your-developer-sandbox-for-red-hat-openshift-from-the-command-line#

Adding the JKube plugin

In pom.xml add in the build/plugins section:

  <plugin>
    <groupId>org.eclipse.jkube</groupId>
    <artifactId>openshift-maven-plugin</artifactId>
    <version>1.7.0</version>
  </plugin>

One line deploy:

$ mvn clean install oc:build oc:resource oc:apply

Check in the topology view to retrieve the URL.

Known issues

Switching from minikube to devsandbox

When oc login ...

error: converting  to : type names don't match (Unknown, RawExtension), and no conversion 'func (runtime.Unknown, runtime.RawExtension) error' registered.

To workaround, I have installed kubectx.

 $ rm ~/.kube -rf
 $ oc login ...

And to recover the minikube config

 $ minikube stop
 $ minikube start

And switch

 $ kubectx sutan-dev/api-sandbox-m2-ll9k-p1-openshiftapps-com:6443/sutan
 $ kubectx minikube