Kubectl
Kind is an amazing tool for running test clusters locally as it runs in a container which makes it lightweight and easy to run throw-away clusters for testing purposes. </br>
Download KUBECTL
We can download kubectl from the Official Docs </br>
Create a kubernetes cluster
In this guide we will run two clusters side by side so we can demonstrate cluster access. </br> Create two clusters:
kind create cluster --name dev --image kindest/node:v1.23.5
kind create cluster --name prod --image kindest/node:v1.23.5
# view cluster info
kubectl cluster-info dump > k8s-info
kubectl config view
See cluster up and running:
kubectl get nodes
NAME STATUS ROLES AGE VERSION
prod-control-plane Ready control-plane,master 2m12s v1.23.5
Understanding the KUBECONFIG
Default location of the kubeconfig file is in <users-directory>/.kube/config
kind: Config
apiVersion: v1
clusters:
- list of clusters (addresses \ endpoints)
users:
- list of users (thing that identifies us when accessing a cluster [certificate])
contexts:
- list of contexts ( which user and cluster to use when running commands)
Commands to interact with kubeconfig are kubectl config. </br>
Key commands are telling kubectl which context to use
kubectl version
kubectl config current-context
kubectl config get-contexts
kubectl config use-context <name>
kubectl describe <resource> <name>
# view cluster api service & port
kubectl get endpoints
NAME ENDPOINTS AGE
kubernetes 192.168.64.13:8443 10d
# viwe svc endpoints
kubectl get endpoints ${SERVICE_NAME}
NAME ENDPOINTS AGE
web-kuboard-press 192.168.144.158:80,192.168.199.135:80 70d
# cnofirm pod numbers are sync with yaml config
kubectl get pods --selector=name=nginx,type=frontend -n ns1
You can also tell your kubectl to use different config files. </br>
This is useful to keep your production config separate from your development ones </br>
Set the $KUBECONFIG environment variable to a path:
#linux
export KUBECONFIG=<path>
#windows
$ENV:KUBECONFIG="C:\Users\aimve\.kube\config"
We can export seperate configs using kind </br>
This is possible with cloud based clusters as well:
kind --name dev export kubeconfig --kubeconfig C:\Users\aimve\.kube\dev-config
kind --name prod export kubeconfig --kubeconfig C:\Users\aimve\.kube\prod-config
#switch to prod
$ENV:KUBECONFIG="C:\Users\aimve\.kube\prod-config"
kubectl get nodes
Working with Kubernetes resources
Now that we have cluster access, next we can read resources from the cluster
with the kubectl get command.
Namespaces
Most kubernetes resources are namespace scoped:
kubectl get namespaces
By default, kubectl commands will run against the default namespace
List resources in a namespace
kubectl get <resource>
kubectl get pods
kubectl get pods --output=wide
kubectl get nodes --show-labels
kubectl get pod redis --watch
kubectl get pod qos-demo -n sandbox --output=yaml
kubectl delete pod qos-demo -n sandbox
kubectl get pv task-pv-volume
kubectl get pvc task-pv-claim
kubectl get deployments
kubectl get services
kubectl get configmaps
kubectl get secrets
kubectl get ingress
kubectl get secret regcred --output="jsonpath={.data.\.dockerconfigjson}" | base64 --decode
kubectl get ingress -n sandbox --watch
kubectl describe ingress ingress-name -n namespace-sandbox
Create resources in a namespace
We can create a namespace with the kubectl create command:
kubectl create ns example-apps
Let’s create a couple of resources:
kubectl -n example-apps create deployment webserver --image=nginx --port=80
kubectl -n example-apps get deploy
kubectl -n example-apps get pods
kubectl -n example-apps create service clusterip webserver --tcp 80:80
kubectl -n example-apps get service
kubectl -n example-apps port-forward svc/webserver 80
# we can access http://localhost/
kubectl -n example-apps create configmap webserver-config --from-file config.json=./kubernetes/kubectl/config.json
kubectl -n example-apps get cm
kubectl -n example-apps create secret generic webserver-secret --from-file secret.json=./kubernetes/kubectl/secret.json
kubectl -n example-apps get secret
# Create files containing the username and password:
echo -n "admin" > ./username.txt
echo -n "1f2d1e2e67df" > ./password.txt
# Package these files into secrets:
kubectl create secret generic user --from-file=./username.txt
kubectl create secret generic pass --from-file=./password.txt
pull image from private registry
# 1. docker login into private registry
docker login
# 2. check credentials, If you use a Docker credentials store, you won't see that `auth` entry but a `credsStore` entry with the name of the store as value. In that case, you can create a `secret` directly
cat ~/.docker/config.json
# 3.a Create a Secret based on existing credentials
kubectl create secret generic regcred \
--from-file=.dockerconfigjson=<path/to/.docker/config.json> \
--type=kubernetes.io/dockerconfigjson
# 3.b Create a Secret by providing credentials on the command line
kubectl create secret docker-registry regcred --docker-server=<your-registry-server> --docker-username=<your-name> --docker-password=<your-pword> --docker-email=<your-email>
Working with YAML
As you can see we can create resources with kubectl but this is only for basic testing purposes.
Kubernetes is a declarative platform, meaning we should provide it what to create instead
of running imperative line-by-line commands. </br>
We can also get the YAML of pre-existing objects in our cluster with the -o yaml flag on the get command </br>
Let’s output all our YAML to a yaml folder:
kubectl -n example-apps get cm webserver-config -o yaml > .\kubernetes\kubectl\yaml\config.yaml
kubectl -n example-apps get secret webserver-secret -o yaml > .\kubernetes\kubectl\yaml\secret.yaml
kubectl -n example-apps get deploy webserver -o yaml > .\kubernetes\kubectl\yaml\deployment.yaml
kubectl -n example-apps get svc webserver -o yaml > .\kubernetes\kubectl\yaml\service.yaml
Create resources from YAML files
The most common and recommended way to create resources in Kubernetes is with the kubectl apply command. </br>
This command takes in declarative YAML files.
To show you how powerful it is, instead of creating things line-by-line, we can deploy all our infrastructure with a single command. </br>
Let’s deploy a Wordpress CMS site, with a back end MySQL database. </br>
This is a snippet taken from my How to learn Kubernetes video:
kubectl create ns wordpress-site
kubectl -n wordpress-site apply --validate -f ./kubernetes/tutorials/basics/yaml/
We can checkout our site with the port-forward command:
kubectl -n wordpress-site get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
mysql ClusterIP 10.96.146.75 <none> 3306/TCP 17s
wordpress ClusterIP 10.96.157.6 <none> 80/TCP 17s
kubectl -n wordpress-site port-forward svc/wordpress 80
Clean up
kind delete cluster --name dev
kind delete cluster --name prod
kubectl delete <resource-type> <resource-name>
kubectl exec -it task-pv-pod -- /bin/bash
kubectl exec my-nginx-3800858182-jr4a2 -- printenv | grep SERVICE
kubectl delete pod task-pv-pod
kubectl delete pvc task-pv-claim
kubectl delete pv task-pv-volume
kubectl delete secret user pass
# add a label
kubectl label nodes <your-node-name> disktype=ssd
kubectl scale deployment my-nginx --replicas=0; kubectl scale deployment my-nginx --replicas=2;
kubectl get pods -l run=my-nginx -o wide
# To mark a Node unschedulable, run:
kubectl cordon $NODENAME