K8s Workloads: Mandatory Fields, YAML Templates & Commands

 

✅  Mandatory Fields Table (VERY IMPORTANT ⭐)

Resource	Mandatory fields
Pod	apiVersion, kind, metadata.name, spec.containers[].name, image
ReplicaSet	apiVersion, kind, metadata.name, spec.selector, spec.template, containers
Deployment	apiVersion, kind, metadata.name, spec.selector, spec.template, containers

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✅ Side-by-Side Comparison (Pod vs RS vs Deployment)

Feature	Pod	ReplicaSet	Deployment
Purpose	Single container	Maintain replicas	Manage RS + rolling updates
Replicas	❌	✅	✅
Self-healing	❌	✅	✅
Rolling update	❌	❌	✅
Rollback	❌	❌	✅
Used in real projects	Rare	Rare	⭐ Mostly used
YAML complexity	Simple	Medium	Medium
Creates	Containers	Pods	RS + Pods

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🔥  Memory Tricks (exam hacks)

🧠 Structure memory

Pod → containers
RS → replicas + selector + template
Deployment → same as RS + rollout features

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🧠 Labels rule (most common mistake)

selector.matchLabels MUST match template.labels

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🧠 apiVersion memory

Pod → v1
RS → apps/v1
Deployment → apps/v1

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🚀 Bonus: Generate YAML quickly

Super useful trick:

kubectl create deployment nginx --image=nginx --dry-run=client -o yaml

kubectl run nginx --image=nginx --dry-run=client -o yaml

👉 No need to memorize full YAML — generate + edit 😄

🔥 Big Idea First (why we use this)

Normally:

❌ Manually writing YAML → error-prone

• wrong indentation

• forgot selector

• wrong apiVersion

• syntax mistakes

Instead:

✅ Let Kubernetes generate perfect YAML for you

Then:
👉 save → edit → apply

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🟢 Command 1

#️⃣

kubectl create deployment nginx --image=nginx --dry-run=client -o yaml

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✅ What it does (simple)

👉 Generates Deployment YAML
👉 Does NOT create anything
👉 Prints YAML to screen

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✅ Breakdown word by word

🔹 kubectl

Kubernetes CLI tool

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🔹 create deployment

Tells kubectl:
👉 "I want to create a Deployment resource"

So it auto builds:

kind: Deployment

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🔹 nginx

Name of deployment

Becomes:

metadata:
  name: nginx

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🔹 --image=nginx

Container image

Becomes:

containers:
- name: nginx
  image: nginx

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🔹 --dry-run=client ⭐ (VERY IMPORTANT)

Means:

👉 "Don't actually create resource"
👉 "Just simulate locally"

If you remove this:

kubectl create deployment nginx --image=nginx

It will really create deployment ❌

With dry-run:
Only preview ✅

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🔹 -o yaml

Output format

Other formats:

-o yaml
-o json
-o wide
-o name

Here:
👉 print YAML

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✅ Output looks like

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx

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✅ Real-world usage

Save to file

kubectl create deployment nginx --image=nginx --dry-run=client -o yaml > deploy.yaml

Edit

vi deploy.yaml

Add:

• replicas

• resources

• ports

• env

Apply

kubectl apply -f deploy.yaml

🔥 This is how pros do it

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🟡 Command 2

#️⃣

kubectl run nginx --image=nginx --dry-run=client -o yaml

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✅ What it does

👉 Generates Pod YAML

NOT Deployment
NOT ReplicaSet
Just single Pod

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✅ Breakdown

🔹 run

Quick way to run a container

Creates:

kind: Pod

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🔹 nginx

Pod name

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🔹 --image=nginx

Container image

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🔹 --dry-run=client

Preview only

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🔹 -o yaml

Print YAML

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✅ Output

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx

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🔥 Deployment vs Run (IMPORTANT DIFFERENCE)

Command	Creates	Use case
kubectl run	Pod	testing/debug
kubectl create deployment	Deployment	production apps

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🎯 When to use which?

✅ For production

kubectl create deployment

Because:

• replicas

• scaling

• rolling update

• rollback

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✅ For quick testing

kubectl run

Because:

• fast

• simple

• temporary

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🔥 Pro DevOps Trick (most useful)

Instead of writing YAML manually:

Step 1

kubectl create deployment myapp --image=nginx --dry-run=client -o yaml > deploy.yaml

Step 2

Edit file

Step 3

kubectl apply -f deploy.yaml

👉 100x faster
👉 zero syntax mistakes
👉 interview smart move

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🧠 Easy memory line

run → Pod
create deployment → Deployment
dry-run → preview only
-o yaml → print YAML