Kubernetes, also known as K8s, is an open-source system for automating deployment, scaling, and management of containerized applications.
Features
- Management of containers: Service discovery/load balancing, secrete and configuration management
- Scale containers: self healing, horizontal scaling
- Storage Orchestration: Robust networking and storage options
Here is the list of useful Kubernetes commands and examples.
Basic Commands
kubectl version
kubectl cluster-info
# pods, deployments, and services
kubectl get all
# create a deployment for a pod
kubectl run <container> -image=<image>
# forward a port wot allow external access
kubectl port-forward <pod> <ports>
# expose a port for a deployment
kubectl expose
kubectl create <resource>
kubectl apply <resource>
Checking Kubernetes is working
kubectl get all
# if you got this error:
# The connection to the server localhost:8080 was refused
# - did you specify the right host or port?
# run the following commands
mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config
Checking Cluster
kubectl cluster-info
Namespaces
- Namespaces provide a scope for names.
kubectl create namespace <ns-name>
kubectl get namespace
kubectl describe namespace <ns-name>
# use -n option to see the resources in the namespace
kubectl get all -n <ns-name>
Kubernetes Objects
Kubernetes API primitives (objects) are the basic building blocks that represent the state of the cluster.
- What kind of applications are running on which nodes
- The resource available to the applications
- The policies that define the behaviors of applications, (restart policies, fault-tolerance, and upgrade)
- Types of Kubernetes Objects: Pods, Nodes, Services, Service Accounts
# list of resources (objects) - name and type
kubectl api-resources
kubectl api-resources -o name #name only
You can retrieve the objects like this:
kubectl get nodes
kubectl get ns # namespaces
kubectl get pods
kubectl get pods -A
kubectl get pods -o wide
kubectl get pods --show-labels
kubectl get deploy
kubectl get rs # replicasets
# horizontal pod autoscaler
kubectl get hpa
kubectl get jobs
kubectl get cj # cronjobs
# persistent volumes
kubectl get pv
# persistent volume claims
kubectl get pvc
kubectl get cm # configMaps
kubectl get secrets
# service accounts
kubectl get sa
kubectl get events
kubectl get svc # services
# resource quotas
kubectl get quota
Managing Kubernetes Objects
You can use the “kubectl” command-line tool to create and manage Kubernetes objects.
- Imperative commands: manage objects directly using a single command
kubectl create deployment nginx --image nginx
- Imperative object configuration: using at least one definition file
kubectl apply -f nginx.yaml
- Declarative object configuration: a user operates on object configuration files stored locally. Create, update, and delete operations are automatically detected per-object by kubectl.
kubectl diff -f configs/
kubectl apply -f configs/
Getting Object Information
- The yaml format is usually used to define the object and its spec.
kubectl get <object-type>
kubectl get pods
kubectl get pods -n kube-system # system pods
kubectl get nodes
kubectl get nodes <node-name>
kubectl get nodes <node-name> -o yaml
kubectl describe node <node-name>
Checking nodes
kubectl get nodes
kubectl describe node <node_name>
Getting Definition Files
kubectl <cmd> --dry-run=client -o yaml
kubectl run <pod-name> --image=<image-name> --dry-run -o yaml
# Examples
kubectl run nginx --image=nginx --dry-run=client -o yaml
kubectl create deployment nginx --image=nginx --dry-run=client -o yaml
kubectl expose pod redis --port=6379 --name redis-service --dry-run=client -o yaml
kubectl create service nodeport nginx-service --tcp=80:80 --node-port=30080 --dry-run=client -o yaml
You can output to the file using:
kubectl <cmd> > <file-name.yaml>
kubectl run <pod-name> --image=<image-name> --dry-run=client -o yaml > pod.yaml
kubectl get <resource> <resource-name> -o yaml > resource.yaml
kubectl get pod <pod-name> -o yaml > pod.yaml
kubectl get pod redis -o yaml > pod.yaml
Deleting resources
#delete pod causes a deployment will recreate a pod
kubectl delete pod <pod-name>
kubectl delete pod <pod-name> --namespace <ns>
#delete a deployment
kubectl delete deployment <deployment-name>
#delete all
kubectl delete all --all --all-namespaces
Container Logs
A container’s normal console output goes into the container log.
- Create a pod with 2 containers that print “Hello, World!”.
apiVersion: v1
kind: Pod
metadata:
name: my-pod
spec:
containers:
- name: my-container1
image: busybox
command: ['echo']
args: ['Hello World! from container 1']
- name: my-container2
image: busybox
command: ['echo']
args: ['Hello World! from container 2']
restartPolicy: Never
- And then check the output using the kubectl logs command.
kubectl logs <pod-name> -c <conainter-name>
# only for a single container pod
kubectl logs my-pod
# for multi-container pod
kubectl logs my-pod –c my-container1
kubectl logs my-pod –c my-container2
Monitoring Pods and Nodes
You can use the kubectl top command to see the resource usage (CPU/Memory/Storage) of pods or nodes.
kubectl top nodes
kubectl top node <node-name>
kubectl top pods
kubectl top pod <pod-name>
