DevOps Classroom notes 06/Jul/2026

DNS in k8s

• In k8s we have lots of pods and accessing each pod by its ip is not a good idea as when pod gets recreated it might not get same ip.
• K8s comes with two possible DNS implementations
  • kube-dns: this was used in early versions of k8s
  • core-dns: This is majorly used in k8s
• DNS in k8s helps in service discovery that is accesing pods by names rather than ephemeral pod ip addresses.

Services in k8s

• Refer Here
• A service can expose with a ip address (fixed) and name which will point to some pods based on labels matched.
• Lets create a new 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:latest
          ports:
            - containerPort: 80

• other manifest

apiVersion: apps/v1
kind: Deployment
metadata:
  name: httpd-deployment
  labels:
    app: httpd
spec:
  replicas: 3
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
        - name: httpd
          image: httpd:2.4
          ports:
            - containerPort: 80

• A serivce in k8s will get a cluster ip (internal ip address)
• A service also gets a name which can be resolved by

<service-name>.<namespace>.svc.cluster.local

• A service can be created without ip address only with a name (headless services)
• Service types
• Lets create a service for nginx pods

apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  selector:
    app: nginx
  type: ClusterIP
  ports:
    - name: web
      port: 80
      protocol: TCP
      targetPort: 80

• A service can be discovered via
  • DNS Resolutions
  • All pods created after the service created will have additional environmental variables injected
• Lets create a nodeport

apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  selector:
    app: nginx
  type: NodePort
  ports:
    - name: web
      port: 80
      protocol: TCP
      targetPort: 80