Introduction to Kubernetes YAML Parameters and Quick Generation of YAML Files

1. Introduction – An overview of Kubernetes resource file YAML parameters.

2. What is YAML – YAML is a markup language similar to XML and JSON that focuses on data representation. For example, SpringBoot’s application.yml is a YAML file.

3. Syntax Rules

Hierarchy is expressed by indentation (spaces only, no tabs).

Typical indentation is two spaces.

YAML is case‑sensitive.

A colon (:) or dash (-) must be followed by a space.

Multiple documents in one file are separated by --- .

Comments start with # .

4. Quickly Generate a YAML File Without Deploying

Run the following command to create an Nginx deployment manifest and save it to nginx1.20.yaml without starting the resource:

kubectl create deployment haha-nginx --image=nginx:1.20.0 -o yaml --dry-run=client > nginx1.20.yaml

Viewing the generated file:

cat nginx1.20.yaml

The resulting YAML (excerpt) is:

apiVersion: apps/v1  # API version
kind: Deployment   # object type
metadata:
  name: haha-nginx
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: haha-nginx
  template:
    metadata:
      labels:
        app: haha-nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.20.0
        resources: {}

5. Interview Question

Difference between kubectl create and kubectl apply :

kubectl create creates a resource the first time; subsequent runs fail because the resource name already exists in the namespace.

kubectl apply also creates the resource on the first run, but on subsequent runs it updates or patches the existing resource based on the manifest, even if the manifest has not changed.

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