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Kubernetes

Kubernetes Config File

  • YAML config file to create and maintain components in a Kubernetes cluster
  • It has 3 parts
    • Metadata
    • Specification
    • Status
      • Stores the actual state of the component
      • Automatically generated and added by K8s from the etcd which stores the status info of every component in the K8s cluster

Sample Config File

nginx-deployment.yaml 

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:            # label the deployment
    app: nginx
spec:                # specifications for the deployment
  replicas: 2
  selector:          # connect all pods with the given label
    matchLabels:
      app: nginx
  template:          # configuration for the pods (config inside config)
    metadata:
      labels:
        app: nginx   # label all the pods
    spec:            # specifications for the pods
      containers:
      - name: nginx
        image: nginx:1.16
        ports:
        - containerPort: 8080  # port at which the container is running

nginx-service.yaml 

apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:          # connect the service with the labelled deployment
    app: nginx
  ports:
    - protocol: TCP
      port: 80          # port at which the service could be contacted
      targetPort: 8080  # port at which pods can be contacted

Connecting Components

  • Metadata contain labels which give key-value pairs to components
  • Specifications contain selectors which select and connect components based on the labels
  • Ports connect Services with Pods.
    • attachments/Pasted image 20220830222705.jpg

Checking connection

Describe the service The endpoints give the IP address and port of the pods that the service will forward the requests to. 

❯ kubectl describe service nginx-service
Name:              nginx-service
Namespace:         default
Labels:            <none>
Annotations:       <none>
Selector:          app=nginx
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                10.105.39.212
IPs:               10.105.39.212
Port:              <unset>  80/TCP
TargetPort:        8080/TCP
Endpoints:         172.17.0.3:8080,172.17.0.4:8080
Session Affinity:  None
Events:            <none>

Get the result of deployment

kubectl get deployment nginx-deployment -o yaml

kubectl get deployment nginx-deployment -o yaml > nginx-deployment-result.yaml
Check the status of the config file. 
status:
  availableReplicas: 2
  conditions:
  - lastTransitionTime: "2022-08-31T03:12:52Z"
    lastUpdateTime: "2022-08-31T03:12:52Z"
    message: Deployment has minimum availability.
    reason: MinimumReplicasAvailable
    status: "True"
    type: Available
  - lastTransitionTime: "2022-08-31T03:12:51Z"
    lastUpdateTime: "2022-08-31T03:12:52Z"
    message: ReplicaSet "nginx-deployment-6986574f5f" has successfully progressed.
    reason: NewReplicaSetAvailable
    status: "True"
    type: Progressing
  observedGeneration: 1
  readyReplicas: 2
  replicas: 2
  updatedReplicas: 2

Last updated: 2022-08-31