Day 23 - Kubernetes Pods

🧠 1. Transition from Docker to Kubernetes

We are moving from Docker (container) to Kubernetes (container orchestration).
In Docker, you directly deploy containers using commands like:

docker run -d -p 8080:80 nginx

But in Kubernetes, you cannot directly deploy a container.
Instead, you deploy your application as a Pod — which is the smallest deployable unit in Kubernetes.

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📦 2. What is a Pod?

A Pod is the basic unit of deployment in Kubernetes.

📘 Definition:
A Pod is a wrapper around one or more containers that defines how a container should run in Kubernetes.

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🧩 Why not deploy containers directly?

Because Kubernetes is a declarative system — it doesn’t want you to manually type commands for every run like Docker.
Instead, Kubernetes expects you to declare the desired state in a file (usually YAML).

Example:

• In Docker → you write:
  docker run -d -p 80:80 nginx

• In Kubernetes → you define a pod.yaml with all specifications.

This allows:

• Standardization across environments

• Easier automation

• Consistency in deployment

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🧾 3. Pod YAML File (Specification)

A Pod is defined using a YAML file.

Example:

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
    - name: nginx
      image: nginx:1.14.2
      ports:
        - containerPort: 80

🟢 This YAML replaces all the Docker CLI flags like:
-p, -v, --network, etc.

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🔄 Equivalent Docker Command

The above YAML is equivalent to:

docker run -d --name nginx -p 80:80 nginx:1.14.2

So, a Pod = Docker container + YAML configuration wrapper.

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👥 4. Single vs Multiple Containers in a Pod

A Pod can have:

• One container (most common)

• Multiple containers (special use-cases)

Why multiple containers?

Some applications need helper containers (sidecars) for:

• Logging

• Config loading

• Proxying traffic

If you place containers inside one Pod:

• They share the same network (localhost)

• They share the same storage volume

Example:

• containerA can talk to containerB using localhost:port

• Both can read/write shared files

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🌐 5. Networking & IPs in Pods

• Each Pod gets a unique Cluster IP (assigned by kube-proxy)

• Containers inside the same Pod share the same IP address

• Other Pods in the cluster can communicate using this Pod IP

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⚙️ 6. Understanding kubectl (Kubernetes CLI)

Like Docker uses docker commands, Kubernetes uses kubectl (pronounced cube control).

Common Commands

👉 All Kubernetes interaction happens through kubectl.

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💻 7. Setting up Kubernetes Locally

For local practice, we use Minikube (lightweight Kubernetes cluster).
Other options include kind, k3s, microk8s.

Steps:

🧩 Step 1: Install kubectl

Search → “install kubectl”
Follow instructions for your OS (Linux/Mac/Windows).

Example for macOS:

brew install kubectl
kubectl version

🧩 Step 2: Install Minikube

Search → “install Minikube”
Then follow commands based on your OS and CPU architecture (Intel/ARM).

Example:

brew install minikube
minikube version

🧩 Step 3: Start the Cluster

minikube start

🖥️ This creates a single-node Kubernetes cluster (1 virtual machine).

In production, you’d have multiple master and worker nodes.
But for learning, 1 node (control plane + worker) is enough.

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🚀 8. Deploying Your First Pod

Create a pod YAML file:

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.14.2
    ports:
    - containerPort: 80

Deploy it:

kubectl create -f pod.yaml

Verify it:

kubectl get pods
kubectl get pods -o wide

Access it inside cluster:

minikube ssh
curl <pod-cluster-ip>

It should return → “Thank you for using nginx”.

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🔍 9. Debugging Pods

If your pod has issues, use:

kubectl describe pod <pod-name>

→ Shows Pod events, errors, status, etc.

To view logs of the application:

kubectl logs <pod-name>

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💡 10. Cleanup

To delete your Pod:

kubectl delete pod <pod-name>

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📘 11. Reference – kubectl Cheat Sheet

For all kubectl commands:
🔗 Kubernetes Official kubectl Cheat Sheet

Keep this handy — even experienced DevOps engineers refer to it.

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⚙️ 12. From Pod → Deployment

You learned:

• Pod = single or multi-container unit

• Defined using YAML

Next step:

• To enable Auto-healing & Auto-scaling,
  you use Deployments — which are wrappers around Pods.

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✅ Summary