Notes-Kubernetes-20feb

Persistent Volume and Persistent Volume Claim:
=============================================
In class Notes:
Problem: 

 > whenever a pod is created, the container will store data 
 > if the pod is deleted , the containers data will be lost
So today we have to find the ways in which we can preserve the data of the container 

 -> preserve data of the container on the Cluster  --> Dev/Test Env -> same as docker
 
 -> preserve data of the container outside the cluster -> Prod Env -> external storage

Storage: Container Storage in Kubernetes 

Volumes in Kubernetes

Recap of volumes in Containers



1. Persistent Volume Claim => PVC -> always created manually
2. Persistent Volume => PV  => manually , dynamically

Manual creation of Volumes in K8s Cluster --> Volume of type -> HostPath --> CKA exam

1. Persistent Volume Claim => PVC
2. Persistent Volume => PV

Dynamic creation of Volumes outside the K8s Cluster -> --> Volume of type -> Persistentdisk --> real time use case

   > Container storge Interface
   > Storage StorageClass

Retain policy for Persistent Volume : 
============================================
Delete : Pod using the volume gets deleted then the volume also get deleted

Retain: Pod using the volume gets deleted but the volume still remains with data retained in the directory

Recycle: Pod using the volume gets deleted then the volume directly gets cleaned up


pdcsi -> It is container storage Interface Pod -> storage driver 

This pod comes by default when the cluster is created on GCP

If you create cluster on AWS --> EBSCSI
If you create cluster on Azure --> blobCSI

However we can also install our own CSI -> netapp, ceph,emc etc


StorageClass => it is not an object of kubernetes => It is just a configuration

StorageClass is like a permission that we give to kubernetes to use of CSI driver to create and manage 
the storage outside the Cluster

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# vim pv.yml

apiVersion: v1
kind: PersistentVolume
metadata:
 name: block-pv 
spec:
 storageClassName: manual
 capacity: 
  storage: 1Gi  
 accessModes:
  - ReadWriteOnce
 persistentVolumeReclaimPolicy: Recycle
 hostPath:    
  path: /tmp/data

# vim pvc.yml


apiVersion: v1
kind: PersistentVolumeClaim
metadata:
 name: pvc
spec:
 storageClassName: manual
 accessModes:
  - ReadWriteOnce  
 resources:
  requests:
   storage: 1Gi

# vim pod-pvc.yml

apiVersion: v1
kind: Pod
metadata:
 name: pod-pvc
spec:
 containers:
  - image: nginx
    name: c1
    volumeMounts:
     - mountPath: "/data"
       name: my-volume
 volumes:
  - name: my-volume
    persistentVolumeClaim:
     claimName: pvc

======================================================

Dynamic Provisioning 


# vim sc.yml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-ssd

# vim pvc-dynamic.yml

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: sc-pvc 
spec:
  storageClassName: fast
  resources:
    requests:
      storage: 10Gi
  accessModes:
    - ReadWriteOnce

# vim pod-dynamic.yml

apiVersion: v1
kind: Pod
metadata:
 name: pod-pvc
spec:
 containers:
  - image: nginx
    name: c1
    volumeMounts:
     - mountPath: "/data"
       name: my-volume
 volumes:
  - name: my-volume
    persistentVolumeClaim:
     claimName: sc-pvc

================================
# kubectl get configmap

# kubectl create configmap dev-config --from-literal=app.mem=2048m

# kubectl get configmap

# kubectl get configmap dev-config -o yaml
# vim dev.properties
app.env:dev
app.mem=2048m
app.properties=dev.env.url
:wq!

# kubectl create configmap dev-config1 --from-file=dev.properties
# kubectl get configmap
# kubectl get configmap dev-config1 -o yaml

Use configmap for a pod

vim pod-configmap.yml

kind: Pod
apiVersion: v1
metadata:
name: pod-configmap
spec:
containers:
 - image: nginx
   name: c1
   volumeMounts:
    - name: config-volume
      mountPath: /etc/config
volumes:
 - name: config-volume
   configMap:
    name: dev-config1
restartPolicy: Never

:wq!

# kubectl apply -f pod-configmap.yml
# kubectl exec -it pod-configmap bash
# cd /etc/config

you will find the dev.properties file and configurations

Edit the configMAP

kubectl edit configmap -n <namespace> <configMapName> -o yaml

This opens up a vim editor with the configmap in yaml format. Now simply edit it and save it.

====================================

Secrets:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql
  labels:
    app: mysql
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mysql
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
        - image: mysql:8
          name: mysql
          env:
            - name: MYSQL_ROOT_PASSWORD
              value: root



===============

echo YWRtaW4= | base64 --decode


kind: Secret
apiVersion: v1
metadata:
   name: wp-mysql
data:
   password: "YWRtaW4="


   apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql
  labels:
    app: mysql
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mysql
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
        - image: mysql:8
          name: mysql
          env:
            - name: MYSQL_ROOT_PASSWORD
              valueFrom:
                secretKeyRef:
                   name: wp-mysql
                   key: password

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