In this article you will learn how to containerize a static website using nginx. Then we will push a private docker image in dockerhub. Finally we will use this private image to be pulled in our Kubernetes cluster ! I will split this article to 2 small and easy steps, you can skip any one you want !

# Containerize a static website and push it on dockerhub

In this Section we will choose a template from random websites that provides free css templates, then we will dockerize it !

# Dockerize the website

I’ll choose this template from this link

Download it and let’s create our Dockerfile !
We will use the nginx:alpine image and copy all the assets of the website to the /usr/share/nginx/html to be hosted by the nginx webserver.

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FROM nginx:alpine
WORKDIR /usr/share/nginx/html
RUN rm -rf ./*
COPY ./ ./
RUN chmod +r -R . 
ENTRYPOINT ["nginx","-g","daemon off;"]

Now it’s time to build the container image

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raf@4n6nk8s:~$ sudo docker build . -t <user_name>/cars-app
Sending build context to Docker daemon  2.454MB
Step 1/5 : FROM nginx:alpine
alpine: Pulling from library/nginx
213ec9aee27d: Downloading [===================================>               ]  2.018MB/2.806MB
2546ae67167b: Downloading [=========>                                         ]  1.461MB/7.403MB
23b845224e13: Download complete
9bd5732789a3: Download complete
328309e59ded: Waiting
b231d02e5150: Waiting

Now let’s create a container to test it before make push it!

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raf@4n6nk8s:~$ sudo docker run --name car-demo -p 8686:80 <user_name>/cars-app
2022/09/08 22:53:47 [notice] 1#1: using the "epoll" event method
2022/09/08 22:53:47 [notice] 1#1: nginx/1.23.1
2022/09/08 22:53:47 [notice] 1#1: built by gcc 11.2.1 20220219 (Alpine 11.2.1_git20220219)
2022/09/08 22:53:47 [notice] 1#1: OS: Linux 5.15.0-41-generic
2022/09/08 22:53:47 [notice] 1#1: getrlimit(RLIMIT_NOFILE): 1048576:1048576
2022/09/08 22:53:47 [notice] 1#1: start worker processes
2022/09/08 22:53:47 [notice] 1#1: start worker process 7
2022/09/08 22:53:47 [notice] 1#1: start worker process 8
2022/09/08 22:53:47 [notice] 1#1: start worker process 9
2022/09/08 22:53:47 [notice] 1#1: start worker process 10

Sanity Check please ! Oh everything is OK !

# Push the container image to private repo

Now go and create a private repository in your dockerhub to push it !

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raf@4n6nk8s:~$ sudo docker image push <user_name>/cars-app
Using default tag: latest
The push refers to repository [docker.io/<user_name>/cars-app]
41c30355eff8: Pushed
f2ba5e032e84: Pushed
43e1f37b87cb: Pushed
bf4e176a4d9b: Mounted from library/nginx
a1d571e4e83d: Mounted from library/nginx
6d97b4d00719: Mounted from library/nginx
2a7647ca3937: Mounted from library/nginx
549c42eea4a6: Mounted from library/nginx
994393dc58e7: Mounted from library/nginx

Now it’s time to deal with our kubernetes cluster !

# Use the private docker image in Kubernetes

In this demo I will use a production kubernetes cluster with 1 master node and 1 worker node

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raf@4n6nk8s:~$ kubectl get nodes
NAME      STATUS   ROLES                  AGE   VERSION
master    Ready    control-plane,master   77d   v1.23.1
worker1   Ready    <none>                 77d   v1.23.1

Let’s create a namespace for this demo !

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raf@4n6nk8s:~$ kubectl create ns private-docker
namespace/private-docker created

To make our cluster pull private images we need to create a special secret object with specific type called docker-registry secret. To make this secret work correctly you must specify the docker registry, username , password and docker email!

I prefer to put this params in variable environment to work with it easly

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export EMAIL=<email>
export USERNAME=<user_name>
export PASSWORD=<password>
export SERVER=<docker_registry>

In case you will use dockerhub as your registry you don’t have to specify the server !

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raf@4n6nk8s:~$ kubectl create -n private-docker secret docker-registry docker-secret --docker-username=$USERNAME --docker-password=$PASSWORD --docker-email=$EMAIL
secret/docker-secret created

Now let’s create a pod with the image that we made it !

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apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: cars-app-pod
  name: cars-app-pod
  namespace: private-docker
spec:
  containers:
  - image: <user_name>/cars-app
    name: cars-app-pod
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

If you try create this pod with this YAML definition you’ll get a ErrImagePull because we don’t specify the docker secret that we created

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raf@4n6nk8s:~$ kubectl get pods -n private-docker
NAME           READY   STATUS         RESTARTS   AGE
cars-app-pod   0/1     ErrImagePull   0          5s

Let’s figure out the problem with kubectl describe command. Take a look at the events that occur when the pod try to pull the container image!

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Events:
 Type     Reason          Age                From               Message
 ----     ------          ----               ----               -------
 Normal   Scheduled       44s                default-scheduler  Successfully assigned private-docker/cars-app-pod to worker1
 Normal   SandboxChanged  40s                kubelet            Pod sandbox changed, it will be killed and re-created.
 Normal   Pulling         26s (x2 over 43s)  kubelet            Pulling image "<user_name>/cars-app"
 Warning  Failed          23s (x2 over 40s)  kubelet            Failed to pull image "<user_name>/cars-app": rpc error: code = Unknown desc = Error response from daemon: pull access denied for <user_name>/cars-app, repository does not exist or may require 'docker login': denied: requested access to the resource is denied
 Warning  Failed          23s (x2 over 40s)  kubelet            Error: ErrImagePull
 Normal   BackOff         12s (x4 over 39s)  kubelet            Back-off pulling image "<user_name>/cars-app"
 Warning  Failed          12s (x4 over 39s)  kubelet            Error: ImagePullBackOff

Specifying the docker secret in the pod YAML definition will solve this problem. The pod will pull the container image without any problem
Adding imagePullSecrets attributes in the spec of the pod allow the pod to pull this image. The Final YAML definition will be similar to the following one !

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apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: cars-app-pod
  name: cars-app-pod
  namespace: private-docker
spec:
  containers:
  - image: <user_name>/cars-app
    name: cars-app-pod
    resources: {}
  imagePullSecrets:
  - name: docker-secret
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

Create the pod again and check it with kubectl get pods and don’t forget to specify the namespace!

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raf@4n6nk8s:~$ kubectl get pods -n private-docker
NAME           READY   STATUS    RESTARTS   AGE
cars-app-pod   1/1     Running   0          4s

I want to make sure that everything is ok, so i will expose this pod using the NodePort service. The following service YAML Definition will expose the pod correctly :

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apiVersion: v1
kind: Service
metadata:
  creationTimestamp: null
  labels:
    run: cars-app-pod
  name: cars-app-pod
  namespace: private-docker
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
  selector:
    run: cars-app-pod
  type: NodePort

Let’s now check the service and get the node port that we will use it to test the pod

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raf@4n6nk8s:~$ kubectl get svc -n private-docker
NAME           TYPE       CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
cars-app-pod   NodePort   10.111.98.22   <none>        80:31651/TCP   6s

Now you can visit either http://master:31651 or http://worker1:31651 and you will find the static website work without any problem!