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
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
