Kubernetes for beginners
pod is a object which encapsulates or groups one or more containers (such as Docker containers), with shared storage/network, and a specification for how to run the containers.
below is the basic structure of pod
apiVersion: v1
kind: Pod
metadata:
name: my-first-app
labels:
type: front-end
spec:
containers:
- name: nginx
image: nginx
-
command to list the pods
kubectl get pods -
command to create a pod with image busybox ( it actually creates deployment )
kubectl run my-pod --image=busybox -
command to delete a particular pod
kubectl delete pod pod_name -
if you have created pod using kubectl run command but you want see configrations of pod, so to get yml out of pod use below command
kubectl get pod pod_name -o yaml > my_pod_file.yaml -
if you want describe your pod
kubectl describe pod pod_name -
if you want to login for running pod
kubectl exec -it pod_name /bin/sh -
if you want access logs of any container inside pod
kubectl logs pod_name -c conatiner_name_inside_pod ( container name inside pod you will get it by kubectl describe pod command ) -
let's say you have created pod using kubectl run command and now you want to change small configuration of pod then you can use below command
kubectl edit pod pod_name ( it will open a vi editor , so you can change and save it back then you no need apply it back kubernetes will automatically updates the pod ) -
let's you have created pods in any other namespaces ( other than default ) , to list them use below command
kubectl get pods --namespace=dev ( assuming namespace is dev )
replicaset is an kubernetes object which is used make your pod highly available and any point time it will make sure sepcified replicas are up and running
basic structure replicaset
apiVersion: apps/v1
kind: ReplicaSet
metadata:
name: my-rs
labels:
type: front-end
spec:
template:
metadata:
name: my-pod
labels:
type: front-end
spec:
containers:
- name: nginx
image: nginx
replicas: 6
selector:
matchLabels:
type: front-end
when you create replica set , it automatically creates pods
-
to list replicaset
kubectl get rs or kubectl get replicasets -
to list replicasets in other name space
kubectl get rs --namespace=dev ( assuming namespace is dev ) -
to delete replicaset
kubectl delete rs rs_name -
lets say replica set has been created via kubectl run command , you want to see configuration file of it
kubectl get rs rs_name -o yaml > rs_sample.yaml -
lets say you want to edit rs
kubectl edit rs rs_name ( it opens vi editor and do the changes , save it back it automatically applies it back ) but one thing to keep in mind is lets you have created rs with image busybox777 and replicas 3 it creates 3 pods with status failed , you will change rs and apply it back but even then pods will with old configuration, so here you have 2 options 1. delete all old pods and now while creating new pods it will take updated configurations 2. delete rs and re-create it -
to increase or decrease replica count without changing rs yaml config file use below command
kubectl scale rs rs_name --replicas=6
You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.
basic structure Deployment
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
labels:
app: nginx
spec:
replicas: 3
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.14.2
ports:
- containerPort: 80
when you create replica set , it automatically creates pods
-
to list deployment
kubectl get deploy or kubectl get deployment -
to list deployment in other name space
kubectl get deploy --namespace=dev ( assuming namespace is dev ) -
to delete deployment
kubectl delete deploy deployment_name -
lets say deployment has been created via kubectl run command , you want to see configuration file of it
kubectl get deploy deployment -o yaml > deploy_sample.yaml -
lets say you want to edit deployment
kubectl edit deploy deployment_name ( it opens vi editor and do the changes , save it back it automatically applies it back ) -
lets say you want to check status of new deployment then use below command
kubectl rollout status deployment_name -
lets say you want to see history of deployment then use below command
kubectl rollout history deployment deployment_name -
if you want play with undo option use below commands
kubectl --record deployment.apps/deployment_name set image deployment.v1.apps/deployemnt_name conatiner_name=deekshithsn/ui kubectl --record deployment.apps/deployment_name set image deployment.v1.apps/deployemnt_name conatiner_name=nginx kubectl rollout undo deployment deployment_name kubectl rollout undo deployment deployment_name --to-revision=1