K8s - Basics

Four keys standards
    - apiVersion
    - kind
    - metadata
    - spec

Create PODs

    apiVersion: v1
    kind: Pod
    metadata:
    name: nginx-prod
    labels:
        name: nginx-prod
        env: production
    spec:
    containers:
    - name: nginx-prod
        image: nginx
        resources:
        limits:
            memory: "240Mi"
            cpu: "500m"
        ports:
        - containerPort: 80

Vinoth@Vinoths-MacBook-Pro httpd-deployment % kubectl get pods
NAME                              READY   STATUS    RESTARTS   AGE
http-deployment-6fbddf8d7-b5qcl   1/1     Running   0          6m23s
http-deployment-6fbddf8d7-cldsq   1/1     Running   0          6m23s
http-deployment-6fbddf8d7-nr97j   1/1     Running   0          6m23s
http-deployment-6fbddf8d7-rhz8m   1/1     Running   0          6m23s
http-deployment-6fbddf8d7-sfhvs   1/1     Running   0          6m23s

Create Replicaset or ReplicationController

ReplicationController - doesn't have ability to automatically update existing replicas (like scale up and down) when they are already running
ReplicaSet - has the ability to modifiy existing replication counts and scales up and download. 

apiVersion: apps/v1
kind: ReplicaSet
metadata:
    name: nginx-prod-replica
spec:
    replicas: 3
    selector:
    matchLabels:
        env: production
    template:
    metadata:
        name: nginx-prod
        labels:
        env: production
    spec:
        containers:
        - name: myapp
            image: nginx
            resources:
            limits:
                memory: "125mi"
                cpu: "250m"
            ports:
            - containerPort: 80

vinoth@Vinoths-MacBook-Pro httpd-deployment % kubectl get replicaset
NAME                        DESIRED   CURRENT   READY   AGE
http-deployment-6fbddf8d7   5         5         5       7m13s

Create Deployment:

To handle deployment strategies RollingUpdate, Recreate 

apiVersion: apps/v1
kind: Deployment
metadata:
name:  http-deployment
labels:
    tier:  http-deployment
spec:
replicas: 5
template:
    metadata:
    labels:
        name:  httpd-frontend
    spec:
    containers:
        - image:  httpd:2.4
        name:  httpd-frontend
        resources:
            limits:
            cpu: "200m"
            memory: "50Mi"
        ports:
            - containerPort: 80
            protocol: TCP    
        env:
            - name:  env
            value:  production
        volumeMounts:
            - name: html
            mountPath: /usr/local/apache2/htdocs/
    volumes:
        - name: html
        configMap:
            name: httpd-config
selector:
    matchLabels:
    name: httpd-frontend
minReadySeconds: 5
strategy:
    type: RollingUpdate
    rollingUpdate:
    #maxSurge: 1
    maxUnavailable: 1


vinoth@Vinoths-MacBook-Pro httpd-deployment % kubectl get deployment
NAME              READY   UP-TO-DATE   AVAILABLE   AGE
http-deployment   5/5     5            5           9m49s

vinoth@Vinoths-MacBook-Pro httpd-deployment % kubectl describe deployment
Name:                   http-deployment
Namespace:              default
CreationTimestamp:      Sat, 05 Nov 2022 18:19:35 +0530
Labels:                 tier=http-deployment
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               name=httpd-frontend
Replicas:               5 desired | 5 updated | 5 total | 5 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        5
RollingUpdateStrategy:  1 max unavailable, 25% max surge
Pod Template:
Labels:  name=httpd-frontend
Containers:
httpd-frontend:
    Image:      httpd:2.4
    Port:       80/TCP
    Host Port:  0/TCP
    Limits:
    cpu:     200m
    memory:  50Mi
    Environment:
    env:  production
    Mounts:
    /usr/local/apache2/htdocs/ from html (rw)
Volumes:
html:
    Type:      ConfigMap (a volume populated by a ConfigMap)
    Name:      httpd-config
    Optional:  false
Conditions:
Type           Status  Reason
----           ------  ------
Available      True    MinimumReplicasAvailable
Progressing    True    NewReplicaSetAvailable
OldReplicaSets:  <none>
NewReplicaSet:   http-deployment-6fbddf8d7 (5/5 replicas created)
Events:
Type    Reason             Age   From                   Message
----    ------             ----  ----                   -------
Normal  ScalingReplicaSet  10m   deployment-controller  Scaled up replica set http-deployment-6fbddf8d7 to 5

Create service for networking and Establish port to access outside node/pods

apiVersion: v1
kind: Service
metadata:
name:  http-service
spec:
type: NodePort
ports:
- port:  80
    targetPort:  80
    protocol: TCP
    nodePort: 30036
selector:
    name: httpd-frontend

Voting app

kubectl exec db-6789fcc76c-hvrs6 -- bash
apt update && apt install vim 
vim /var/lib/postgresql/data/pg_hba.conf (update trust)
su - postgres
    psql
    SELECT pg_reload_conf();
    \q
kubectl logs db-6789fcc76c-hvrs6

Waiting for db
Waiting for db
Waiting for db
Connected to db
Found redis at 10.111.128.34
Connecting to redis
Processing vote for 'a' by 'd9aa8912c8ce5f81'
Processing vote for 'b' by 'd9aa8912c8ce5f81'
Processing vote for 'a' by 'd9aa8912c8ce5f81'
Processing vote for 'b' by 'd9aa8912c8ce5f81'
Processing vote for 'a' by 'd9aa8912c8ce5f81'
Processing vote for 'b' by 'd9aa8912c8ce5f81'
Processing vote for 'b' by '2806bb8c6d5e587e'
Processing vote for 'a' by 9461d629e0325e84'