What is a yaml file in Kubernetes?

 YAML Basics:-

•       YAML is not a Markup Language

•       YAML is used to store information about different things

•       We can use YAML  to define key, Value pairs like variables, lists and objects

•       YAML is very similar to JSON (Javascript Object Notation)

•       YAML primarily focuses on readability and user friendliness

•       YAML is designed to be clean and easy to read

•       We can define YAML files with two different extensions

        abc.yml

        abc.yaml

1.YAML Comments

2.YAML Key Value Pairs

3.YAML Dictionary or Map

4.YAML Array / Lists

5.YAML Spaces

6.YAML Document Separator

Step-01: Comments & Key Value Pairs

Space after the colon is mandatory to differentiate key and value

# Defining simple key-value pairs

Basic unit: key: value

name: motu

age: 23

city: noida

Use # to add comments

# This is a comment

name: John  # Inline comment

Step-02: Dictionary / Map

Set of properties grouped together after an item

Equal amount of blank space is required for all the items under a dictionary

person:  # Dictionary

  name: motu

  age: 23

  city: noida

Step-03: Array / Lists

Dash indicates an element of an array

Use - to denote each item in a list.

person: # Dictionary

  name: motu

  age: 23

  city: Hyderabad

  hobbies: # List 

    - cycling

    - cookines

# Or inline style:

 hobbies: [cycling, cooking]   # List with a different notation  

Step-04: Multiple Lists

Dash indicates an element of an array

person: # Dictionary

  name: motu

  age: 23

  city: Hyderabad

  hobbies: # List 

    - cycling

    - cooking

  hobbies: [cycling, cooking]   # List with a different notation 

  friends: # multiple lists

    - name: friend1

      age: 22

    - name: friend2

      age: 25           

Step-05: YAML Spaces (Indentation)

• YAML is space-sensitive (use spaces, not tabs).
• Indentation indicates nesting.
• Standard: 2 spaces per level (not enforced, but common).

person:

  name: John

  address:

    city: Mumbai

    pin: 400001

Step-06: YAML Document Separator

• Use --- to separate multiple documents in one file.
• ... (optional) indicates the end of a document.

---

name: Alice

age: 25

---

name: Bob

age: 28

...

Step-07: Kubernetes YAML Top-level Objects

# Types of Kubernetes Objects

# Pod, ReplicaSet, Deployment, Service and many more

Pod API Objects Reference

https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.26/#pod-v1-core

apiVersion:

kind:

metadata:

spec: 

# apiVersion: version of k8s objects

# kind: k8s objects

# metadata: define name and labels for k8s objects

# spec: specification or real definition for k8s objects

Step-08: Sample Pod Template for Reference

apiVersion: v1 # String

kind: Pod  # String

metadata: # Dictionary

  name: myapp-pod

  labels: # Dictionary

    app: myapp        

spec:

  containers: # List

    - name: myapp

      image: stacksimplify/kubenginx:1.0.0

      ports:  # List

        - containerPort: 80

Dry Run (syntax + context check without applying):

# kubectl apply -f yourfile.yaml --dry-run=client

Check specific resources:

# kubectl explain deployment

# kubectl explain deployment.spec

# kubectl apply -f 01-pod-definition.yml

# kubectl get pods