Introduction

If you are getting started with containers, you will likely want to know how to automate building, testing, and deployment. By taking a Cloud Native approach to these processes, you can leverage the right infrastructure APIs to package and deploy applications in an automated way.

Two building blocks for doing automation include container images and container orchestrators. Over the last year or so, Kubernetes has become the default choice for container orchestration. In this first article of the CI/CD with Kubernetes series, you will:

• Build container images with Docker, Buildah, and Kaniko.
• Set up a Kubernetes cluster with Terraform, and create Deployments and Services.
• Extend the functionality of a Kubernetes cluster with Custom Resources.

By the end of this tutorial, you will have container images built with Docker, Buildah, and Kaniko, and a Kubernetes cluster with Deployments, Services, and Custom Resources.

Future articles in the series will cover related topics: package management for Kubernetes, CI/CD tools like Jenkins X and Spinnaker, Services Meshes, and GitOps.

Prerequisites

• An Ubuntu 16.04 server with a non-root user account. Follow our Initial Server Setup with Ubuntu 16.04 tutorial for guidance.
• Docker installed on your server. Please follow Steps 1 and 2 of How To Install and Use Docker on Ubuntu 16.04 for installation instructions.
• A Docker Hub account. For an overview on getting started with Docker Hub, please see these instructions.
  
• A DigitalOcean account and personal access token. Please refer to these instructions to get your access token.
• Familiarity with containers and Docker. Please refer to the Webinar Series: Getting Started with Containers for more details.
• Familiarity with Kubernetes concepts. Please refer to An Introduction to Kubernetes for more details.

Step 1 — Building Container Images with Docker and Buildah

A container image is a self-contained entity with its own application code, runtime, and dependencies that you can use to create and run containers. You can use different tools to create container images, and in this step you will build containers with two of them: Docker and Buildah.

Building Container Images with Dockerfiles

Docker builds your container images automatically by reading instructions from a Dockerfile, a text file that includes the commands required to assemble a container image. Using the docker image build command, you can create an automated build that will execute the command-line instructions provided in the Dockerfile. When building the image, you will also pass the build context with the Dockerfile, which contains the set of files required to create an environment and run an application in the container image.

Typically, you will create a project folder for your Dockerfile and build context. Create a folder called demo to begin:

mkdir demo
cd demo

Next, create a Dockerfile inside the demo folder:

nano Dockerfile

Add the following content to the file:

FROM ubuntu:16.04

LABEL MAINTAINER neependra@cloudyuga.guru

RUN apt-get update \
    && apt-get install -y nginx \
    && apt-get clean \
    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* \
    && echo "daemon off;" >> /etc/nginx/nginx.conf

EXPOSE 80
CMD ["nginx"]

This Dockerfile consists of a set of instructions that will build an image to run Nginx. During the build process ubuntu:16.04 will function as the base image, and the nginx package will be installed. Using the CMD instruction, you've also configured nginx to be the default command when the container starts.

Next, you'll build the container image with the docker image build command, using the current directory (.) as the build context. Passing the -t option to this command names the image nkhare/nginx:latest:

sudo docker image build -t nkhare/nginx:latest .

You will see the following output:

Output
Sending build context to Docker daemon  49.25MB
Step 1/5 : FROM ubuntu:16.04
 ---> 7aa3602ab41e
Step 2/5 : MAINTAINER neependra@cloudyuga.guru
 ---> Using cache
 ---> 552b90c2ff8d
Step 3/5 : RUN apt-get update     && apt-get install -y nginx     && apt-get clean     && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*     && echo "daemon off;" >> /etc/nginx/nginx.conf
 ---> Using cache
 ---> 6bea966278d8
Step 4/5 : EXPOSE 80
 ---> Using cache
 ---> 8f1c4281309e
Step 5/5 : CMD ["nginx"]
 ---> Using cache
 ---> f545da818f47
Successfully built f545da818f47
Successfully tagged nginx:latest

Your image is now built. You can list your Docker images using the following command:

docker image ls

Output
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
nkhare/nginx        latest              4073540cbcec        3 seconds ago       171MB
ubuntu              16.04               7aa3602ab41e        11 days ago     

You can now use the nkhare/nginx:latest image to create containers.

Building Container Images with Project Atomic-Buildah

Buildah is a CLI tool, developed by Project Atomic, for quickly building Open Container Initiative (OCI)-compliant images. OCI provides specifications for container runtimes and images in an effort to standardize industry best practices.

Buildah can create an image either from a working container or from a Dockerfile. It can build images completely in user space without the Docker daemon, and can perform image operations like build, list, push, and tag. In this step, you'll compile Buildah from source and then use it to create a container image.

To install Buildah you will need the required dependencies, including tools that will enable you to manage packages and package security, among other things. Run the following commands to install these packages:

 cd
 sudo apt-get install software-properties-common
 sudo add-apt-repository ppa:alexlarsson/flatpak
 sudo add-apt-repository ppa:gophers/archive
 sudo apt-add-repository ppa:projectatomic/ppa
 sudo apt-get update
 sudo apt-get install bats btrfs-tools git libapparmor-dev libdevmapper-dev libglib2.0-dev libgpgme11-dev libostree-dev libseccomp-dev libselinux1-dev skopeo-containers go-md2man

Because you will compile the buildah source code to create its package, you'll also need to install Go:

sudo apt-get update
sudo curl -O https://storage.googleapis.com/golang/go1.8.linux-amd64.tar.gz
sudo tar -xvf go1.8.linux-amd64.tar.gz
sudo mv go /usr/local
sudo echo 'export PATH=$PATH:/usr/local/go/bin' >> ~/.profile
source ~/.profile
go version 

You will see the following output, indicating a successful installation:

Output
go version go1.8 linux/amd64

You can now get the buildah source code to create its package, along with the runc binary. runc is the implementation of the OCI container runtime, which you will use to run your Buildah containers.

Run the following commands to install runc and buildah:

mkdir ~/buildah
cd ~/buildah
export GOPATH=`pwd`
git clone https://github.com/projectatomic/buildah ./src/github.com/projectatomic/buildah
cd ./src/github.com/projectatomic/buildah
make runc all TAGS="apparmor seccomp"
sudo cp ~/buildah/src/github.com/opencontainers/runc/runc /usr/bin/.
sudo apt install buildah 

Next, create the /etc/containers/registries.conf file to configure your container registries:

sudo nano /etc/containers/registries.conf

Add the following content to the file to specify your registries:

# This is a system-wide configuration file used to
# keep track of registries for various container backends.
# It adheres to TOML format and does not support recursive
# lists of registries.

# The default location for this configuration file is /etc/containers/registries.conf.

# The only valid categories are: 'registries.search', 'registries.insecure',
# and 'registries.block'.

[registries.search]
registries = ['docker.io', 'registry.fedoraproject.org', 'quay.io', 'registry.access.redhat.com', 'registry.centos.org']

# If you need to access insecure registries, add the registry's fully-qualified name.
# An insecure registry is one that does not have a valid SSL certificate or only does HTTP.
[registries.insecure]
registries = []

# If you need to block pull access from a registry, uncomment the section below
# and add the registries fully-qualified name.
#
# Docker only
[registries.block]
registries = []

The registries.conf configuration file specifies which registries should be consulted when completing image names that do not include a registry or domain portion.

Now run the following command to build an image, using the https://github.com/do-community/rsvpapp repository as the build context. This repository also contains the relevant Dockerfile:

sudo buildah build-using-dockerfile -t rsvpapp:buildah github.com/do-community/rsvpapp 

This command creates an image named rsvpapp:buildah from the Dockerfille available in the https://github.com/do-community/rsvpapp repository.

To list the images, use the following command:

sudo buildah images

You will see the following output:

Output
IMAGE ID             IMAGE NAME                                               CREATED AT             SIZE
b0c552b8cf64         docker.io/teamcloudyuga/python:alpine                    Sep 30, 2016 04:39     95.3 MB
22121fd251df         localhost/rsvpapp:buildah                                Sep 11, 2018 14:34     114 MB

One of these images is localhost/rsvpapp:buildah, which you just created. The other, docker.io/teamcloudyuga/python:alpine, is the base image from the Dockerfile.

Once you have built the image, you can push it to Docker Hub. This will allow you to store it for future use. You will first need to login to your Docker Hub account from the command line:

docker login -u your-dockerhub-username -p your-dockerhub-password

Once the login is successful, you will get a file, ~/.docker/config.json, that will contain your Docker Hub credentials. You can then use that file with buildah to push images to Docker Hub.

For example, if you wanted to push the image you just created, you could run the following command, citing the authfile and the image to push:

sudo buildah push --authfile ~/.docker/config.json rsvpapp:buildah docker://your-dockerhub-username/rsvpapp:buildah

You can also push the resulting image to the local Docker daemon using the following command:

sudo buildah push rsvpapp:buildah docker-daemon:rsvpapp:buildah

Finally, take a look at the Docker images you have created:

sudo docker image ls

Output
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
rsvpapp             buildah             22121fd251df        4 minutes ago       108MB
nkhare/nginx        latest              01f0982d91b8        17 minutes ago      172MB
ubuntu              16.04               b9e15a5d1e1a        5 days ago          115MB

As expected, you should now see a new image, rsvpapp:buildah, that has been exported using buildah.

You now have experience building container images with two different tools, Docker and Buildah. Let's move on to discussing how to set up a cluster of containers with Kubernetes.

Step 2 — Setting Up a Kubernetes Cluster on DigitalOcean using kubeadm and Terraform

There are different ways to set up Kubernetes on DigitalOcean. To learn more about how to set up Kubernetes with kubeadm, for example, you can look at How To Create a Kubernetes Cluster Using Kubeadm on Ubuntu 18.04.

Since this tutorial series discusses taking a Cloud Native approach to application development, we'll apply this methodology when setting up our cluster. Specifically, we will automate our cluster creation using kubeadm and Terraform, a tool that simplifies creating and changing infrastructure.

Using your personal access token, you will connect to DigitalOcean with Terraform to provision 3 servers. You will run the kubeadm commands inside of these VMs to create a 3-node Kubernetes cluster containing one master node and two workers.

On your Ubuntu server, create a pair of SSH keys, which will allow password-less logins to your VMs:

ssh-keygen -t rsa

You will see the following output:

Output
Generating public/private rsa key pair.
Enter file in which to save the key (~/.ssh/id_rsa): 

Press ENTER to save the key pair in the ~/.ssh directory in your home directory, or enter another destination.

Next, you will see the following prompt:

Output
Enter passphrase (empty for no passphrase): 

In this case, press ENTER without a password to enable password-less logins to your nodes.

You will see a confirmation that your key pair has been created:

Output
Your identification has been saved in ~/.ssh/id_rsa.
Your public key has been saved in ~/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:lCVaexVBIwHo++NlIxccMW5b6QAJa+ZEr9ogAElUFyY root@3b9a273f18b5
The key's randomart image is:
+---[RSA 2048]----+
|++.E ++o=o*o*o   |
|o   +..=.B = o   |
|.    .* = * o    |
| .   =.o + *     |
|  . . o.S + .    |
|   . +.    .     |
|    . ... =      |
|        o= .     |
|       ...       |
+----[SHA256]-----+

Get your public key by running the following command, which will display it in your terminal:

cat ~/.ssh/id_rsa.pub

Add this key to your DigitalOcean account by following these directions.

Next, install Terraform:

sudo apt-get update
sudo apt-get install unzip
wget https://releases.hashicorp.com/terraform/0.11.7/terraform_0.11.7_linux_amd64.zip
unzip terraform_0.11.7_linux_amd64.zip
sudo mv terraform /usr/bin/.
terraform version

You will see output confirming your Terraform installation:

Output
Terraform v0.11.7

Next, run the following commands to install kubectl, a CLI tool that will communicate with your Kubernetes cluster, and to create a ~/.kube directory in your user's home directory:

sudo apt-get install apt-transport-https
curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -
sudo touch /etc/apt/sources.list.d/kubernetes.list 
echo "deb http://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee -a /etc/apt/sources.list.d/kubernetes.list
sudo apt-get update
sudo apt-get install kubectl
mkdir -p ~/.kube

Creating the ~/.kube directory will enable you to copy the configuration file to this location. You’ll do that once you run the Kubernetes setup script later in this section. By default, the kubectl CLI looks for the configuration file in the ~/.kube directory to access the cluster.

Next, clone the sample project repository for this tutorial, which contains the Terraform scripts for setting up the infrastructure:

git clone https://github.com/do-community/k8s-cicd-webinars.git

Go to the Terrafrom script directory:

cd k8s-cicd-webinars/webinar1/2-kubernetes/1-Terraform/

Get a fingerprint of your SSH public key:

ssh-keygen -E md5 -lf ~/.ssh/id_rsa.pub | awk '{print $2}'

You will see output like the following, with the highlighted portion representing your key:

Output
MD5:dd:d1:b7:0f:6d:30:c0:be:ed:ae:c7:b9:b8:4a:df:5e

Keep in mind that your key will differ from what's shown here.

Save the fingerprint to an environmental variable so Terraform can use it:

export FINGERPRINT=dd:d1:b7:0f:6d:30:c0:be:ed:ae:c7:b9:b8:4a:df:5e

Next, export your DO personal access token:

export TOKEN=your-do-access-token

Now take a look at the ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terraform/ project directory:

ls

Output
cluster.tf  destroy.sh  files outputs.tf  provider.tf  script.sh

This folder contains the necessary scripts and configuration files for deploying your Kubernetes cluster with Terraform.

Execute the script.sh script to trigger the Kubernetes cluster setup:

./script.sh

When the script execution is complete, kubectl will be configured to use the Kubernetes cluster you've created.

List the cluster nodes using kubectl get nodes:

kubectl get nodes

Output
NAME                STATUS    ROLES     AGE       VERSION
k8s-master-node     Ready     master    2m        v1.10.0
k8s-worker-node-1   Ready     <none>    1m        v1.10.0
k8s-worker-node-2   Ready     <none>    57s       v1.10.0

You now have one master and two worker nodes in the Ready state.

With a Kubernetes cluster set up, you can now explore another option for building container images: Kaniko from Google.

Step 3 — Building Container Images with Kaniko

Earlier in this tutorial, you built container images with Dockerfiles and Buildah. But what if you could build container images directly on Kubernetes? There are ways to run the docker image build command inside of Kubernetes, but this isn't native Kubernetes tooling. You would have to depend on the Docker daemon to build images, and it would need to run on one of the Pods in the cluster.

A tool called Kaniko allows you to build container images with a Dockerfile on an existing Kubernetes cluster. In this step, you will build a container image with a Dockerfile using Kaniko. You will then push this image to Docker Hub.

In order to push your image to Docker Hub, you will need to pass your Docker Hub credentials to Kaniko. In the previous step, you logged into Docker Hub and created a ~/.docker/config.json file with your login credentials. Let's use this configuration file to create a Kubernetes ConfigMap object to store the credentials inside the Kubernetes cluster. The ConfigMap object is used to store configuration parameters, decoupling them from your application.

To create a ConfigMap called docker-config using the ~/.docker/config.json file, run the following command:

sudo kubectl create configmap docker-config --from-file=$HOME/.docker/config.json

Next, you can create a Pod definition file called pod-kaniko.yml in the ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terraform/ directory (though it can go anywhere).

First, make sure that you are in the ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terraform/ directory:

cd ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terraform/

Create the pod-kaniko.yml file:

nano pod-kaniko.yml

Add the following content to the file to specify what will happen when you deploy your Pod. Be sure to replace your-dockerhub-username in the Pod's args field with your own Docker Hub username:

apiVersion: v1
kind: Pod
metadata:
  name: kaniko
spec:
  containers:
  - name: kaniko
    image: gcr.io/kaniko-project/executor:latest
    args: ["--dockerfile=./Dockerfile",
            "--context=/tmp/rsvpapp/",
            "--destination=docker.io/your-dockerhub-username/rsvpapp:kaniko",
            "--force" ]
    volumeMounts:
      - name: docker-config
        mountPath: /root/.docker/
      - name: demo
        mountPath: /tmp/rsvpapp
  restartPolicy: Never
  initContainers:
    - image: python
      name: demo
      command: ["/bin/sh"]
      args: ["-c", "git clone https://github.com/do-community/rsvpapp.git /tmp/rsvpapp"] 
      volumeMounts:
      - name: demo
        mountPath: /tmp/rsvpapp
  restartPolicy: Never
  volumes:
    - name: docker-config
      configMap:
        name: docker-config
    - name: demo
      emptyDir: {}

This configuration file describes what will happen when your Pod is deployed. First, the Init container will clone the Git repository with the Dockerfile, https://github.com/do-community/rsvpapp.git, into a shared volume called demo. Init containers run before application containers and can be used to run utilties or other tasks that are not desirable to run from your application containers. Your application container, kaniko, will then build the image using the Dockerfile and push the resulting image to Docker Hub, using the credentials you passed to the ConfigMap volume docker-config.

To deploy the kaniko pod, run the following command:

kubectl apply -f pod-kaniko.yml 

You will see the following confirmation:

Output
pod/kaniko created

Get the list of pods:

kubectl get pods

You will see the following list:

Output
NAME      READY     STATUS     RESTARTS   AGE
kaniko    0/1       Init:0/1   0          47s

Wait a few seconds, and then run kubectl get pods again for a status update:

kubectl get pods

You will see the following:

Output
NAME      READY     STATUS    RESTARTS   AGE
kaniko    1/1       Running   0          1m

Finally, run kubectl get pods once more for a final status update:

kubectl get pods

Output
NAME      READY     STATUS      RESTARTS   AGE
kaniko    0/1       Completed   0          2m

This sequence of output tells you that the Init container ran, cloning the GitHub repository inside of the demo volume. After that, the Kaniko build process ran and eventually finished.

Check the logs of the pod:

kubectl logs kaniko

You will see the following output:

Output
time="2018-08-02T05:01:24Z" level=info msg="appending to multi args docker.io/your-dockerhub-username/rsvpapp:kaniko"
time="2018-08-02T05:01:24Z" level=info msg="Downloading base image nkhare/python:alpine"
.
.
.
ime="2018-08-02T05:01:46Z" level=info msg="Taking snapshot of full filesystem..."
time="2018-08-02T05:01:48Z" level=info msg="cmd: CMD"
time="2018-08-02T05:01:48Z" level=info msg="Replacing CMD in config with [/bin/sh -c python rsvp.py]"
time="2018-08-02T05:01:48Z" level=info msg="Taking snapshot of full filesystem..."
time="2018-08-02T05:01:49Z" level=info msg="No files were changed, appending empty layer to config."
2018/08/02 05:01:51 mounted blob: sha256:bc4d09b6c77b25d6d3891095ef3b0f87fbe90621bff2a333f9b7f242299e0cfd
2018/08/02 05:01:51 mounted blob: sha256:809f49334738c14d17682456fd3629207124c4fad3c28f04618cc154d22e845b
2018/08/02 05:01:51 mounted blob: sha256:c0cb142e43453ebb1f82b905aa472e6e66017efd43872135bc5372e4fac04031
2018/08/02 05:01:51 mounted blob: sha256:606abda6711f8f4b91bbb139f8f0da67866c33378a6dcac958b2ddc54f0befd2
2018/08/02 05:01:52 pushed blob sha256:16d1686835faa5f81d67c0e87eb76eab316e1e9cd85167b292b9fa9434ad56bf
2018/08/02 05:01:53 pushed blob sha256:358d117a9400cee075514a286575d7d6ed86d118621e8b446cbb39cc5a07303b
2018/08/02 05:01:55 pushed blob sha256:5d171e492a9b691a49820bebfc25b29e53f5972ff7f14637975de9b385145e04
2018/08/02 05:01:56 index.docker.io/your-dockerhub-username/rsvpapp:kaniko: digest: sha256:831b214cdb7f8231e55afbba40914402b6c915ef4a0a2b6cbfe9efb223522988 size: 1243

From the logs, you can see that the kaniko container built the image from the Dockerfile and pushed it to your Docker Hub account.

You can now pull the Docker image. Be sure again to replace your-dockerhub-username with your Docker Hub username:

docker pull your-dockerhub-username/rsvpapp:kaniko

You will see a confirmation of the pull:

Output
kaniko: Pulling from your-dockerhub-username/rsvpapp
c0cb142e4345: Pull complete 
bc4d09b6c77b: Pull complete 
606abda6711f: Pull complete 
809f49334738: Pull complete 
358d117a9400: Pull complete 
5d171e492a9b: Pull complete 
Digest: sha256:831b214cdb7f8231e55afbba40914402b6c915ef4a0a2b6cbfe9efb223522988
Status: Downloaded newer image for your-dockerhub-username/rsvpapp:kaniko

You have now successfully built a Kubernetes cluster and created new images from within the cluster. Let's move on to discussing Deployments and Services.

Step 4 — Create Kubernetes Deployments and Services

Kubernetes Deployments allow you to run your applications. Deployments specify the desired state for your Pods, ensuring consistency across your rollouts. In this step, you will create an Nginx deployment file called deployment.yml in the ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terraform/ directory to create an Nginx Deployment.

First, open the file:

nano deployment.yml

Add the following configuration to the file to define your Nginx Deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

This file defines a Deployment named nginx-deployment that creates three pods, each running an nginx container on port 80.

To deploy the Deployment, run the following command:

kubectl apply -f deployment.yml

You will see a confirmation that the Deployment was created:

Output
deployment.apps/nginx-deployment created

List your Deployments:

kubectl get deployments

Output
NAME               DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   3         3         3            3           29s

You can see that the nginx-deployment Deployment has been created and the desired and current count of the Pods are same: 3.

To list the Pods that the Deployment created, run the following command:

kubectl get pods

Output
NAME                                READY     STATUS      RESTARTS   AGE
kaniko                              0/1       Completed   0          9m
nginx-deployment-75675f5897-nhwsp   1/1       Running     0          1m
nginx-deployment-75675f5897-pxpl9   1/1       Running     0          1m
nginx-deployment-75675f5897-xvf4f   1/1       Running     0          1m

You can see from this output that the desired number of Pods are running.

To expose an application deployment internally and externally, you will need to create a Kubernetes object called a Service. Each Service specifies a ServiceType, which defines how the service is exposed. In this example, we will use a NodePort ServiceType, which exposes the Service on a static port on each node.

To do this, create a file, service.yml, in the ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terrafrom/ directory:

nano service.yml

Add the following content to define your Service:

kind: Service
apiVersion: v1
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  type: NodePort
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
    nodePort: 30111

These settings define the Service, nginx-service, and specify that it will target port 80 on your Pod. nodePort defines the port where the application will accept external traffic.

To deploy the Service run the following command:

kubectl apply -f service.yml

You will see a confirmation:

Output
service/nginx-service created

List the Services:

kubectl get service

You will see the following list:

Output
NAME            TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
kubernetes      ClusterIP   10.96.0.1       <none>        443/TCP        5h
nginx-service   NodePort    10.100.98.213   <none>        80:30111/TCP   7s

Your Service, nginx-service, is exposed on port 30111 and you can now access it on any of the node’s public IPs. For example, navigating to http://node_1_ip:30111 or http://node_2_ip:30111 should take you to Nginx's standard welcome page.

Once you have tested the Deployment, you can clean up both the Deployment and Service:

kubectl delete deployment nginx-deployment
kubectl delete service nginx-service

These commands will delete the Deployment and Service you have created.

Now that you have worked with Deployments and Services, let's move on to creating Custom Resources.

Step 5 — Creating Custom Resources in Kubernetes

Kubernetes offers limited but production-ready functionalities and features. It is possible to extend Kubernetes' offerings, however, using its Custom Resources feature. In Kubernetes, a resource is an endpoint in the Kubernetes API that stores a collection of API objects. A Pod resource contains a collection of Pod objects, for instance. With Custom Resources, you can add custom offerings for networking, storage, and more. These additions can be created or removed at any point.

In addition to creating custom objects, you can also employ sub-controllers of the Kubernetes Controller component in the control plane to make sure that the current state of your objects is equal to the desired state. The Kubernetes Controller has sub-controllers for specified objects. For example, ReplicaSet is a sub-controller that makes sure the desired Pod count remains consistent. When you combine a Custom Resource with a Controller, you get a true declarative API that allows you to specify the desired state of your resources.

In this step, you will create a Custom Resource and related objects.

To create a Custom Resource, first make a file called crd.yml in the ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terrafrom/ directory:

nano crd.yml

Add the following Custom Resource Definition (CRD):

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: webinars.digitalocean.com
spec:
  group: digitalocean.com
  version: v1
  scope: Namespaced
  names:
    plural: webinars
    singular: webinar
    kind: Webinar
    shortNames:
    - wb

To deploy the CRD defined in crd.yml, run the following command:

kubectl create -f crd.yml 

You will see a confirmation that the resource has been created:

Output
customresourcedefinition.apiextensions.k8s.io/webinars.digitalocean.com created

The crd.yml file has created a new RESTful resource path: /apis/digtialocean.com/v1/namespaces/*/webinars. You can now refer to your objects using webinars, webinar, Webinar, and wb, as you listed them in the names section of the CustomResourceDefinition. You can check the RESTful resource with the following command:

kubectl proxy & curl 127.0.0.1:8001/apis/digitalocean.com

sudo ufw allow 8001

You will see the following output:

Output
HTTP/1.1 200 OK
Content-Length: 238
Content-Type: application/json
Date: Fri, 03 Aug 2018 06:10:12 GMT

{
    "apiVersion": "v1", 
    "kind": "APIGroup", 
    "name": "digitalocean.com", 
    "preferredVersion": {
        "groupVersion": "digitalocean.com/v1", 
        "version": "v1"
    }, 
    "serverAddressByClientCIDRs": null, 
    "versions": [
        {
            "groupVersion": "digitalocean.com/v1", 
            "version": "v1"
        }
    ]
}

Next, create the object for using new Custom Resources by opening a file called webinar.yml:

nano webinar.yml

Add the following content to create the object:

apiVersion: "digitalocean.com/v1"
kind: Webinar
metadata:
  name: webinar1
spec:
  name: webinar
  image: nginx

Run the following command to push these changes to the cluster:

kubectl apply -f webinar.yml 

You will see the following output:

Output
webinar.digitalocean.com/webinar1 created

You can now manage your webinar objects using kubectl. For example:

kubectl get webinar

Output
NAME       CREATED AT
webinar1   21s

You now have an object called webinar1. If there had been a Controller, it would have intercepted the object creation and performed any defined operations.

Deleting a Custom Resource Definition

To delete all of the objects for your Custom Resource, use the following command:

kubectl delete webinar --all

You will see:

Output
webinar.digitalocean.com "webinar1" deleted

Remove the Custom Resource itself:

kubectl delete crd webinars.digitalocean.com

You will see a confirmation that it has been deleted:

Output
customresourcedefinition.apiextensions.k8s.io "webinars.digitalocean.com" deleted

After deletion you will not have access to the API endpoint that you tested earlier with the curl command.

This sequence is an introduction to how you can extend Kubernetes functionalities without modifying your Kubernetes code.

Step 6 — Deleting the Kubernetes Cluster

To destroy the Kubernetes cluster itself, you can use the destroy.sh script from the ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terrafrom folder. Make sure that you are in this directory:

cd ~/k8s-cicd-webinars/webinar1/2-kubernetes/1-Terrafrom

Run the script:

./destroy.sh

By running this script, you'll allow Terraform to communicate with the DigitalOcean API and delete the servers in your cluster.

Conclusion

In this tutorial, you used different tools to create container images. With these images, you can create containers in any environment. You also set up a Kubernetes cluster using Terraform, and created Deployment and Service objects to deploy and expose your application. Additionally, you extended Kubernetes' functionality by defining a Custom Resource.

You now have a solid foundation to build a CI/CD environment on Kubernetes, which we'll explore in future articles.