my-docs/kubernetes/workloads/replicaset.md

Document: Kubernetes ReplicaSet YAML Explanation

Overview

This document provides an explanation of a Kubernetes ReplicaSet YAML file and commands to manage the ReplicaSet. The YAML file defines the desired state for a ReplicaSet, which ensures a specified number of pod replicas are running at any given time.

YAML File Breakdown

1. Define the ReplicaSet

The YAML file begins with the apiVersion, kind, and metadata fields, which specify the API version, the type of Kubernetes object, and metadata about the object, respectively.

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: my-app
  namespace: my-ns
  labels:
    app.kubernetes.io/name: my-app
    app.kubernetes.io/env: development

• apiVersion: apps/v1: Specifies that this configuration uses the apps/v1 API version.
• kind: ReplicaSet: Defines the object as a ReplicaSet.
• metadata: Provides metadata for the ReplicaSet, including:
  • name: The name of the ReplicaSet (my-app).
  • namespace: The namespace where the ReplicaSet will be created (my-ns).
  • labels: Key-value pairs to categorize the ReplicaSet (app.kubernetes.io/name: my-app and app.kubernetes.io/env: development).

2. Define the Specification

The spec section describes the desired state of the ReplicaSet.

spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: my-app
  template:
    metadata:
      labels:
        app.kubernetes.io/name: my-app
    spec:
      containers:
      - name: nginx
        image: nginx

• replicas: 3: Specifies that three replicas of the pod should be running.
• selector: Defines how to identify the pods managed by this ReplicaSet.
  • matchLabels: Matches pods with the label app.kubernetes.io/name: my-app.
• template: Provides the pod template used by the ReplicaSet to create new pods.
  • metadata: Metadata for the pod template.
    • labels: Labels applied to the pods (app.kubernetes.io/name: my-app).
  • spec: Describes the pod specification.
    • containers: Defines the containers within the pod.
      • name: The name of the container (nginx).
      • image: The container image to use (nginx).

Update the Container Image Version

To update the container image version, edit the YAML manifest and change the image field:

containers:
- name: nginx
  image: nginx:1.25

Apply the updated manifest to update the pods with the new image version.

Complete YAML File with Image Version Update

Here is the complete YAML file with the container image version updated to nginx:1.25:

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: my-app
  namespace: my-ns
  labels:
    app.kubernetes.io/name: my-app
    app.kubernetes.io/env: development
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: my-app
  template:
    metadata:
      labels:
        app.kubernetes.io/name: my-app
    spec:
      containers:
      - name: nginx
        image: nginx:1.25