In Kubernetes, labels and selectors are key concepts used to identify and organize objects within the cluster. Labels are key-value pairs attached to Kubernetes objects, such as pods, services, or deployments, allowing you to categorize and group them based on your requirements. Selectors, on the other hand, are used to query and filter objects based on their labels.

Here's a breakdown of labels and selectors in Kubernetes:

Labels:

Labels are arbitrary metadata that you can attach to Kubernetes objects.
They consist of key-value pairs, where both the key and value are strings.
Labels are typically used to describe the characteristics or properties of objects.
You can assign multiple labels to an object, allowing for flexible grouping and categorization.
Labels are not unique across objects and can be shared among different resources.

Selectors:

Selectors are used to query and filter objects based on their labels.
They allow you to define rules to select a specific set of objects that match the label criteria.
Selectors use label-matching expressions to specify the criteria for object selection.
There are two types of selectors: equality-based selectors and set-based selectors.
Equality-based selectors match labels based on exact key-value matches.
Set-based selectors support more advanced label-matching operations, such as set membership and set intersection.
Selectors are commonly used in various Kubernetes features, such as service discovery, deployments, and replica sets.

Prerequisite:

Created three deployments with different labels as follows:

Deployment one is named mydep1 with labels as class=unnati and course=cka.
Deployment two is named mydep2 with labels as class=cidco and course=cca.
Deployment three is named mydep3 with labels as class=darga course=rhcsa.

Yaml files for all deployments:

#Yaml file for deployment one (mydep1)

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    class: unnati
    course: cka
  name: mydep1
spec:
  replicas: 6
  selector:
    matchLabels:  
      class: unnati 
      course: cka
  strategy: {}
  template:
    metadata:
      labels:
        class: unnati
        course: cka
    spec:
      containers:
      - image: docker.io/httpd
        name: httpd
        resources: {}
status: {}

#Yaml file deployment two (mydep2)

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    class: cidco
    course: cca
  name: mydep2
spec:
  replicas: 5
  selector:
    matchLabels:
      class: cidco
      course: cca
  strategy: {}
  template:
    metadata:
      labels:
        class: cidco
        course: cca
    spec:
      containers:
      - image: docker.io/httpd
        name: httpd
        resources: {}
status: {}

#Yaml file for deployment three (mydep3)

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    class: darga
    course: rhcsa
  name: mydep3
spec:
  replicas: 4
  selector:
    matchLabels:
      class: darga
      course: rhcsa
  strategy: {}
  template:
    metadata:
      labels:
        class: darga
        course: rhcsa
    spec:
      containers:
      - image: docker.io/httpd
        name: httpd
        resources: {}
status: {}

Equity-based selectors & Set-based selectors:-