Kubernetes In Action

Journey With Pods & Storage

Learning Outcome(Slide2)

Earlier we have seen

How to create a web application

How to containerize applications using Docker

How to push images to Docker Hub

How to deploy applications in Kubernetes

Now we will learn how Kubernetes manages running containers

using Pods and stores application data using storage systems 

Understanding the concept

Imagine a warehouse storing packages

• Packages are grouped together in boxes

• Multiple boxes are created to ensure availability

• A manager monitors the boxes and replaces damaged ones

 In Kubernetes:

• Pods are like boxes containing containers

• ReplicaSets ensure multiple pods exist

• Storage systems safely store application data

What is a Pod?

A Pod is the smallest deployable unit in Kubernetes.

A Pod contains one or more containers.

Containers inside a pod share:

• Network

• Storage

• Configuration

Pods run the actual application containers.

Example

A Pod may contain:

• Web server container

• Logging container

Important points:

• Pods are temporary

• If a Pod fails, Kubernetes can create a new one automatically

Pods allow containers to work together as a single application unit.

Pod Characteristics

Pods have several key characteristics.

Shared Network

Containers inside the same pod share the same IP address and port space

Shared Storage

Containers can share volumes inside the pod.

Single Application Unit

Pods usually run one main container, but can run multiple supporting containers.

Ephemeral Nature

Pods are not permanent.

If a pod crashes:

Kubernetes creates a new replacement pod.

Introduction to ReplicaSet

A ReplicaSet ensures that a specified number of Pods are always running.

Example:

If you define 3 replicas, Kubernetes ensures:

3 Pods are always active.

If one pod fails:

Kubernetes automatically creates a new Pod.

ReplicaSets help with:

• High availability

• Fault tolerance

• Load distribution

ReplicaSets are commonly used inside Deployments.

Managing Pods with ReplicaSets

ReplicaSets continuously monitor running pods.

Workflow:

User defines desired replicas

Example:

replicas: 3

Kubernetes checks current state:

• If pods < 3 → create new pods

• If pods > 3 → remove extra pods

Example Scenario:

Desired Pods = 3

Running Pods = 2

Kubernetes will create 1 additional Pod automatically.

ReplicaSets ensure applications remain available and stable.

Storage Challenges in Containers

Containers are temporary by design.

When a container stops or is deleted:

All data inside the container is lost.

Example problem:

A database container stores data.

If the container crashes:

The database data disappears.

This creates major problems for:

• Databases

• User uploads

• Logs

• Application state

To solve this problem, Kubernetes provides persistent storage solutions.

Storage Solutions in Kubernetes

Kubernetes provides storage through Volumes.

A Volume allows containers to store data outside the container filesystem.

Benefits:

• Data survives container restart

• Multiple containers can share data

• Storage can connect to external systems

Volumes allow applications to store important data safely.

Kubernetes manages storage through:

• Persistent Volumes

• Persistent Volume Claims

Types of Persistent Storage

Kubernetes supports multiple storage types.

Persistent Volume (PV)

A Persistent Volume is a piece of storage in the cluster.

It can come from:

• Local disk

• Cloud storage

• Network storage

Persistent Volume Claim (PVC)

A PVC is a request for storage by a user or application.

Example:

Application requests:

• 5GB storage

• Read/Write access

Kubernetes connects the request to a suitable Persistent Volume.

Core Concepts (Slide 7)

Storage Classes

Storage Classes allow dynamic storage provisioning.

This automatically creates storage when applications request it.

Lifecycle of Persistent Storage

Persistent storage follows a lifecycle.

1. Provisioning

Storage is created manually or dynamically.

2. Binding

A Persistent Volume Claim connects to a Persistent Volume.

3. Usage

Pods use the storage through mounted volumes.

4. Reclaiming

After the PVC is deleted, storage can:

• Be reused

• Be retained

• Be deleted

This lifecycle ensures efficient storage management.

 How Pods Use Persistent Storage

Pods access storage using volume mounts.

Workflow:

Application requests storage (PVC)

⬇

Kubernetes assigns Persistent Volume

⬇

Pod mounts storage volume

⬇

Application writes data to storage

Now data remains safe even if pods restart or move to another node.

Summary

What is the main purpose of a ReplicaSet in Kubernetes?

What is the main purpose of a ReplicaSet in Kubernetes?

Which platform is mainly used for professional networking and B2B marketing ?