kubectl, the kubernetes CLI¶

pods¶

Create pods¶

There are 3 differnet ways to create pods from kubectl CLI

kubectl run (run single pod per command)
kubectl create (create resources via CLI or YAML)
kubectl apply (create/update resources via YAML)

Create ngnix web-server pod

kubectl run mhs-nginx --image nginx

List Pods¶

This will show pods only in the default namespace

kubectl get pods

List pods with custom namespace

kubectl get pods --namespace=kube-system

List pods with IP address

kubectl get pod -o wide

List pods& refresh continously

kubectl get pods -o wide -w

Cluster info

kubectl cluster-info

Describe pods¶

kubectl describe pod mhs-nginx

Delete pods¶

kubectl delete pod mhs-nginx

SSH into a pod¶

kubectl exec -it hello -- /bin/sh

Nodes¶

Get Nodes

kubectl get nodes

Namespaces¶

In Kubernetes, namespaces provides a mechanism for isolating groups of resources within a single cluster.

Kubernetes starts with four initial namespaces:

default The default namespace for objects with no other namespace
kube-system The namespace for objects created by the Kubernetes system
kube-public This namespace is created automatically and is readable by all users (including those not authenticated). This namespace is mostly reserved for cluster usage, in case that some resources should be visible and readable publicly throughout the whole cluster. The public aspect of this namespace is only a convention, not a requirement.
kube-node-lease This namespace holds Lease objects associated with each node. Node leases allow the kubelet to send heartbeats so that the control plane can detect node failure.

List all namespaces in cluster

kubectl get namespaces

Start a pod with namespace

kubectl run nginx --image=nginx --namespace=<insert-namespace-name-here>

Deployments¶

Deployment managed by the Kubernetes Deployment controller tells Kubernetes how to create or modify instances of the pods that hold a containerized application. A Deployment runs multiple replicas of your application and automatically replaces any instances that fail or become unresponsive.

Create/scale deployment¶

kubectl create deployment nginx-deploy --image=nginx

Get deployment details¶

kubectl describe deployment nginx-deploy

Scale deployment¶

kubectl scale deployment nginx-deploy --replicas=5

Update deployment with new image¶

kubectl set image deployment k8s-hello k8s-hello=nginx:latest

Check rollout status¶

kubectl  rollout status deploy k8s-hello

Remove deployment¶

kubectl delete deployment nginx-deploy

Rollout¶

Get rollout status

kubectl rollout status name

Get rollout history/revision

kubectl rollout history name

Undo rollout deployment

 kubectl rollout undo deployment myapp-deployment

Deployment strategies¶

Recreate¶

This strategy will terminate all the old pods and then create new ones with the new configuration. This will cause downtime.

Rolling Update¶

This strategy will create new pods with the new configuration and then terminate the old ones gradually. It will create new pods with the new configuration and then terminate the old ones gradually. This will not cause downtime. This is the default strategy.

Services¶

Create a ClusterIP¶

Expose a internal port 80 to the external port 8080

kubectl expose deployment nginx-deploy --port=8080 --target-port=80

Warning

ClusterIP service will allow connecting from inside the kubernetes cluster. Used when we want to block connections from outside the kubernetes cluster but want the cluster itself to have access.

Create a NodePort¶

kubectl expose deployment k8s-hello --type=NodePort --port=3000

Info

NodePort service will allow connecting from outside the kubernetes cluster

Create a LoadBalancer¶

kubectl expose deployment k8s-hello --type=LoadBalancer --port=3000

Info

NodePort service will allow connecting from outside the kubernetes cluster

List services¶

kubectl get svc

Get Service Details

kubectl describe service nginx-deploy

Delete service

kubectl delete service nginx-deploy

Get all objects in the default namespace

kubectl get all

Cleanup¶

Delete all resources the default namespace

kubectl delete all --all

Tip

This also deletes the default kubernetes(ClusterIP) service but it is re-created automatically

Replicas¶

Replication Controller¶

Get Replication Controller

kubectl get rc

Replica Set¶

Get Replica Set

kubectl get rs

Scale Replica Set

kubectl scale --replicas=5 -f replicaset replicaset.yml

kubectl scale rs --replicas=5 replicaset

Warning

This will create 5 replicas of the pods defined in the replicaset.yml file but does not update the replicaset.yml file

Edit Replica Set Inline

kubectl edit rs replicaset

Info

This will open the replicaset.yml file in the default editor and any changes made will be applied immediately to the replicaset

YAML Configuration¶

Every kubernetes configuration file has 3 parts

metadata Eg: name & labels
specification Eg: spec
status, automatically generated by kubernetes

Apply configuration¶

kubectl apply -f filename.yml

Delete configuration¶

kubectl delete -f filename.yml