{"id":304,"date":"2023-03-09T11:31:28","date_gmt":"2023-03-09T10:31:28","guid":{"rendered":"https:\/\/pierre.porcheret.org\/?p=304"},"modified":"2023-08-21T15:53:29","modified_gmt":"2023-08-21T13:53:29","slug":"basic-kubernetes-usage","status":"publish","type":"post","link":"https:\/\/pierre.porcheret.org\/en\/computer\/304\/","title":{"rendered":"Basic Kubernetes usage"},"content":{"rendered":"

Please read the Kubernetes installation if needed<\/a><\/p>\n\n\n\n

How kubernetes works ?<\/p>\n\n\n\n

Kubernetes will first need a Namespace where we will push pods (containers).<\/p>\n\n\n\n

Here, for example, we will create a Namespace called \u00ab\u00a0webserver\u00a0\u00bb where we will run nginx pods.<\/p>\n\n\n\n

The workflow will consist of create a Namespace (If no Namespace is defined, it will use a \u00ab\u00a0default\u00a0\u00bb one), deploy a Pod image with an image (here nginx) and expose them in the kubernetes cluster.<\/p>\n\n\n\n

All will be done on Master Node<\/p>\n\n\n\n

Namespace configuration<\/h2>\n\n\n\n

To create the Namespace, just do :<\/p>\n\n\n\n

kubectl create namespace webwerver<\/code><\/pre>\n\n\n\n
Most of the time, you can also use shorter commands in kubernetes, for example here<\/p>\n\n\n\n
kubectl create ns webserver<\/code><\/pre>\n\n\n\n
Note that this Namespace’s name must be in lowercase <\/p>\n\n\n\n
You can delete Namespace using <\/p>\n\n\n\n
kubectl delete namespace webserver<\/code><\/pre>\n\n\n\n
To view your Namespace use :<\/p>\n\n\n\n
kubectl get namespaces<\/code><\/pre>\n\n\n\n
You will see all the current namespace created and network namespace if you use for example Calico.<\/p>\n\n\n\n
Deployement and services<\/h2>\n\n\n\n
You must create a deployment and services in order to push them in pods.<\/p>\n\n\n\n
For that, you have many ways to do this.<\/p>\n\n\n\n
Using only commands :<\/h3>\n\n\n\n
Create the deployment :<\/p>\n\n\n\n
kubectl create deployment nginx --image=nginx -n webserver<\/code><\/pre>\n\n\n\n
Create the associate service:<\/p>\n\n\n\n
kubectl create service nodeport nginx --tcp=80:80 -n webserver<\/code><\/pre>\n\n\n\n
Or better,<\/p>\n\n\n\n
Use an YAML file <\/h3>\n\n\n\n
apiVersion: apps\/v1
kind: Deployment
metadata:
    name: nginx
spec:
   selector:
      matchLabels:
         app: nginx
   replicas: 2
   template:
      metadata:
          labels:
             app: nginx
          spec:
            containers:
              - name: nginx
                 image: nginx:stable
                 ports:
                    - containerPort: 80<\/code><\/pre>\n\n\n\n
Here we have :<\/p>\n\n\n\n
    \n
  • kind: type of file (here deployment)<\/li>\n\n\n\n
  • replicas: number of desired pods (here 2)<\/li>\n\n\n\n
  • image: Image’s name<\/li>\n\n\n\n
  • containerPort: exposed port (here the host port will be set automatically)<\/li>\n<\/ul>\n\n\n\n
    You can then apply your YAML file in your Namespace using :<\/p>\n\n\n\n
    kubectl apply -f nginx.yaml -n webserver<\/code><\/pre>\n\n\n\n
    Of course, change the YAML file’s name according to your file.<\/p>\n\n\n\n
    I prefer this method with YAML file because if you have to rebuild your application, you will just have to run the YAML file again, and you don’t have to remember the parameters you used. It also provides the deployment specification and services in one shot.<\/p>\n\n\n\n
    Once you ran your deployment, you can, as the Namespace, check or delete them :<\/p>\n\n\n\n
    kubectl get deployments -n webserver<\/code><\/pre>\n\n\n\n
    kubectl delete deployments nginx -n webserver<\/code><\/pre>\n\n\n\n
    Expose you deployment \/ service<\/h2>\n\n\n\n
    You have now created your application with the configuration (port, number of pods, image)<\/p>\n\n\n\n
    You can now push and activate them (expose them)<\/p>\n\n\n\n
    kubectl expose deployment nginx --type=NodePort -n webserver<\/code><\/pre>\n\n\n\n
    It will create the number of \u00ab\u00a0replica\u00a0\u00bb pods in your kubernetes cluster and expose the specified port.<\/p>\n\n\n\n
    You can check this service and get the host port:<\/p>\n\n\n\n
    kubectl get service nginx -n webserver<\/code><\/pre>\n\n\n\n
    You should have an output like :<\/p>\n\n\n\n
    NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE\nnginx NodePort 10.101.82.65 80:3272\/TCP 26s<\/code><\/pre>\n\n\n\n
    Here, we have the service nginx listening on port 80 internally and expose to the port 3272 in host.<\/p>\n\n\n\n
    You can also have more info using this command:<\/p>\n\n\n\n
    kubectl describe service nginx -n webserver<\/code><\/pre>\n\n\n\n
    Patches, Scale and other commands<\/h2>\n\n\n\n
    Patching<\/h3>\n\n\n\n
    Patch can be used to change on the fly, for example, the host port if you want to specify a new one :<\/p>\n\n\n\n
    kubectl patch service nginx -n webserver --type='json' --patch='[{\"op\": \"replace\", \"path\": \"\/spec\/ports\/0\/nodePort\", \"value\":31001}]'<\/code><\/pre>\n\n\n\n
    For example, here, we force the service nginx to get the host port 31001 instead of the previous 3272.<\/p>\n\n\n\n
    Scale<\/h3>\n\n\n\n
    Scale is used to increase the desire replica (or pods) or to unexposed them:<\/p>\n\n\n\n
    kubectl scale deployment nginx -n webserver –replicas=3<\/p>\n\n\n\n
    kubectl scale deployment nginx -n webserver –replicas=0<\/p>\n\n\n\n
    Endpoints (describe)<\/h3>\n\n\n\n
    Ok you create pods…but you may want to know where they are no ? You can for that use the previous describe command:<\/p>\n\n\n\n
    kubectl describe service nginx -n webserver | grep \"Endpoints\"<\/code><\/pre>\n\n\n\n
    Point to take care<\/h2>\n\n\n\n
    The common error is to forget to add the Namespace if you use one, just check if you specify it in all your commands :<\/p>\n\n\n\n
    <command> -n namespce<\/code><\/pre>\n\n\n\n
    Don’t forget to check at each step what you did before doing the next step <\/p>\n\n\n\n
    kubectk get <pods,deploymenets,services....><\/code><\/pre>\n\n\n\n
    <\/p>","protected":false},"excerpt":{"rendered":"
    Please read the Kubernetes installation if needed How kubernetes works ? Kubernetes will first need a Namespace where we will push pods (containers). Here, for example, we will create a Namespace called \u00ab\u00a0webserver\u00a0\u00bb where we will run nginx pods. The workflow will consist of create a Namespace (If no Namespace […]<\/p>\n","protected":false},"author":1,"featured_media":289,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"two_page_speed":null,"footnotes":""},"categories":[8,41,9],"tags":[42,43,28],"class_list":["post-304","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-computer","category-devops","category-linux","tag-bases","tag-devops","tag-kubernetes"],"yoast_head":"\nBasic Kubernetes usage -<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/pierre.porcheret.org\/en\/computer\/304\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Basic Kubernetes usage -\" \/>\n<meta property=\"og:description\" content=\"Please read the Kubernetes installation if needed How kubernetes works ? 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