2025-01-09 k8s manifest files

ReplicaSets

The ReplicaSet configuration defines a number of identical pods required, and if a pod is evicted or fails, creates more pods to compensate for the loss. ReplicaSets are usually not used directly—they are typically created as part of a deployment.

Here is a simple example using matchLabels as the selector. rs.yaml

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: frontend
  labels:
    app: guestbook
    tier: frontend
spec:
  # modify replicas according to your case
  replicas: 3
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        tier: frontendn
    spec:
      containers:
      - name: nginx
        image: nginx

Apply Manifest kubectl apply -f rs.yaml

Note: use either one file naming yml or yaml

Deployment

Deployments are one level up from ReplicaSets. They allow you to use a declarative method to deploy ReplicaSets and pods. You use YAML configuration to define what your group of pods should look like, and the deployment manipulates Kubernetes objects to create pods exactly according to the YAML specification.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend
  labels:
    app: guestbook
    tier: frontend
spec:
  # modify replicas according to your case
  replicas: 3
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        tier: frontendn
    spec:
      containers:
      - name: nginx
        image: nginx

deployment ----> ReplicaSet -------> Pods

Services

In a Kubernetes cluster, each Pod has an internal IP address. But the Pods in a Deployment come and go, and their IP addresses change. So it doesn’t make sense to use Pod IP addresses directly. With a Service, you get a stable IP address that lasts for the life of the Service, even as the IP addresses of the member Pods change.

A key aim of Services in Kubernetes is that you don’t need to modify your existing application to use an unfamiliar service discovery mechanism. You can run code in Pods, whether this is a code designed for a cloud-native world, or an older app you’ve containerized. You use a Service to make that set of Pods available on the network so that clients can interact with it.

Types of Kubernetes Services

Types	Short Codes	Description
LoadBalancer	lb	Clients send requests to the IP address of a network load balancer.
NodePort	np	Clients send requests to the IP address of a node on one or more nodePort values that are specified by the Service.
ClusterIp	cip	Internal clients send requests to a stable internal IP address.
ExternalName	xn	Internal clients use the DNS name of a Service as an alias for an external DNS name.
Headless	-	You can use a headless service when you want a Pod grouping, but don’t need a stable IP address.

Hot Tip

Its not possible to remember all shortcodes for k8’s Resources Thats why we have this command to Lists all the resources in cluster

kubectl api-resources

Two ways to use Kubernetes

Imperative Way	Declarative Way
commands	Manifest