Kubectl for Docker Beginners
Kubectl is a command line interface for running commands against Kubernetes clusters. kubectl looks for a file named config in the $HOME/.kube directory. You can specify other kubeconfig files by setting the $KUBECONFIG environment variable or by setting the --kubeconfig flag.
Example: Running Nginx Service
PWD:
docker run -d --restart=always -e DOMAIN=cluster --name nginx-app -p 80:80 nginx
[node4 ~]$ docker exec -it 9dc env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=9dc0816328dcTERM=xterm
DOMAIN=cluster
NGINX_VERSION=1.17.6
NJS_VERSION=0.3.7
PKG_RELEASE=1~buster
HOME=/root
PWK:
Start the pod running nginx
kubectl run --image=nginx nginx-app --port=80 --env="DOMAIN=cluster"
Accessing the app on browser
kubectl port-forward nginx-app 80:80
Expose a port through with a service
kubectl expose deployment nginx-app --port=80 --name=nginx-http
[node1 replicaset101]$ kubectl get po,svc,deploy
NAME READY STATUS RESTARTS AGE
pod/nginx-app-7c58988fb9-sckpd 1/1 Running 0 3m12s
pod/portainer-8586dccbb5-x66vk 1/1 Running 1 49m
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 53m
service/nginx-http ClusterIP 10.108.29.166 <none> 80/TCP 2m11s
service/portainer LoadBalancer 10.98.58.121 <pending> 80:32001/TCP 49m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.extensions/nginx-app 1/1 1 1 3m15s
deployment.extensions/portainer 1/1 1 1 49m
[node1 replicaset101]$ curl 10.108.29.166:80
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
}
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
Example: Listing Containers Vs Pods
PWD
docker ps -a
PWK
kubectl get po
Example: Attach a process that is already running in a container
docker ps
docker attach <containerid>
kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-app-5jyvm 1/1 Running 0 10m
kubectl attach -it nginx-app-5jyvm
...
Example: To execute a command in a container,
PWD
docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
55c103fa1296 nginx "nginx -g 'daemon of…" 6 minutes ago Up 6 minutes 0.0.0.0:80->80/tcp nginx-app
docker exec 55c103fa1296 cat /etc/hostname
55c103fa1296
PWK
kubectl get po
NAME READY STATUS RESTARTS AGE
nginx-app-5jyvm 1/1 Running 0 10m
kubectl exec nginx-app-5jyvm -- cat /etc/hostname
nginx-app-5jyvm
Example: To use interactive commands.
PWD
docker exec -ti 55c103fa1296 /bin/sh
# exit
PWK
kubectl exec -ti nginx-app-5jyvm -- /bin/sh
# exit
Example: To follow stdout/stderr of a process that is running
PWD
docker logs -f a9e
192.168.9.1 - - [14/Jul/2015:01:04:02 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.35.0" "-"
192.168.9.1 - - [14/Jul/2015:01:04:03 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.35.0" "-"
PWK
kubectl logs -f nginx-app-zibvs
10.240.63.110 - - [14/Jul/2015:01:09:01 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.26.0" "-"
10.240.63.110 - - [14/Jul/2015:01:09:02 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.26.0" "-"
kubectl logs --previous nginx-app-zibvs
10.240.63.110 - - [14/Jul/2015:01:09:01 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.26.0" "-"
10.240.63.110 - - [14/Jul/2015:01:09:02 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.26.0" "-"