Kubernetes

 Kubernetes Overview and kubectl



 * What is Kubernetes?


- Kubernetes (K8S) is an open-source tool for managing containers, developed by Google. 
- It allows you to deploy, manage, and scale containerised applications automatically.

* Why Kubernetes?

Before containers:

- Developers created applications and passed them to the Operations team. 
- Ops teams faced challenges with setups, dependencies, and configurations.

With containers (like Docker):

- Developers bundle applications and dependencies into images. 
- These images work the same in any environment (development, testing, production).
- However, managing many containers requires automation; this is where orchestration comes in.

* What is Container Orchestration?


Container orchestration automates:

- Deploying containers
- Connecting containers
- Scaling containers up or down
- Managing failures
- Allocating resources
- Kubernetes is one orchestration tool among others, like Docker Swarm and Apache Mesos.

* Key Benefits of Kubernetes


- High availability: the application keeps running even if a node fails.
- Load balancing: it spreads traffic across containers.
- Auto-scaling: it adds or removes containers based on demand.
- Node scaling: it adjusts hardware without any downtime.
- Declarative configuration: it uses simple YAML files.


* Core Kubernetes Concepts






1. Node

- A worker machine, either physical or virtual.
- It runs containers and was previously called a minion. 

2. Cluster

- A group of multiple nodes.
It offers:
- High availability
- Load sharing
- Fault tolerance

3. Master Node (Control Plane)

- This node manages the cluster.
It is responsible for:
- Monitoring nodes
- Scheduling containers
- Handling failures
- Maintaining cluster state

4. kubectl (Kube Control CLI)

- This command-line tool lets you interact with Kubernetes.
Common commands include:
- kubectl run: Deploy an application
- kubectl cluster-info: View cluster details
- kubectl get nodes: List all nodes

* Summary

Kubernetes helps you:
- Run containers efficiently
- Manage failures automatically
- Scale applications smoothly
- Handle infrastructure with straightforward configuration files
- It is the industry standard for container orchestration.

Lab : kubectl


* How many nodes are part of cluster?




The Kubernetes control plane URL can be found by running the command 



Create a Pod named nginx-pod using the nginx image.



Is pod running?



Kubernetes Pods


* What is a Pod?


- A Pod is the smallest unit you can deploy in Kubernetes.
- It holds your application container, usually one container per Pod.
- Kubernetes does not run containers directly on nodes; it runs Pods.
- 1 Pod = 1 Application Instance
- A Pod usually has one container running one instance of your application.
- For example, a single Nginx container inside a Pod.

* Scaling Applications


- To scale your app for more users:
- Do not add more containers to the same Pod.
- Do create new Pods with the same container image.
- Scaling up means creating more Pods.
- Scaling down means deleting Pods.

* Pods Across Nodes

- If one node is full, Kubernetes schedules Pods on other nodes in the cluster.
- More demand means more Pods, which may lead to more nodes.

* Can a Pod Have Multiple Containers?

- Yes, but only when they perform supporting tasks, not for scaling.

Examples:
- Main Web App container
- Helper container, like a logs processor or file parser

These containers:
- Run together inside the same Pod
- Start and stop together
- Share the same network and storage
- This arrangement is known as sidecar containers.

* Deploying Pods

You can use the kubectl run command:
- kubectl run nginx --image=nginx

This command:
- Creates a Pod
- Pulls the container image from Docker Hub or your private repository
- Runs the container inside the Pod

* Viewing Pods

Use this command:
- kubectl get pods

Pod states include:
- ContainerCreating means the container image is being downloaded.
- Running means the Pod is up and running successfully.

* Summary

- Pods are the basic building blocks in Kubernetes.
- One Pod equals one instance of your app.
- To scale, increase or decrease the number of Pods, not the containers inside a Pod.
- Pods can have multiple containers, but only when they work together.
- Using kubectl commands makes it easy to deploy and manage Pods.

Lab : Pods

* How many pods exist on the system?



* Create a new pod with the nginx image.





Which nodes are these pods placed on?



What is the state of the pod webapp?




YAML Basics


* What is YAML?  

- YAML stands for YAML Ain’t Markup Language.  
- It is used to represent configuration data.  
- It is easier to read than XML and JSON because of its clean, indentation-based structure.  

YAML vs XML vs JSON  



- XML uses opening and closing tags and is heavy.  
- JSON uses curly braces {} and brackets [].  
- YAML is simple, clean, and human-readable; it uses indentation instead of brackets.  

* YAML Key-Value Format  

Basic structure:  
- key: value  

Examples:  

fruit: apple  
vegetable: carrot  
liquid: water  
meat: chicken  

* Important:  

- Use a space after the colon.  
- No quotes are needed unless there are special characters.  

* YAML Lists (Arrays)  

Lists are represented using dashes (-):  
fruits:  
  - apple  
  - banana  
  - mango  

* YAML Dictionaries (Objects)  

- A dictionary is a group of key-value pairs under one item:  
banana:  
  calories: 105  
  fat: 0.4  
  carbs: 27  

* Important:  

- Indentation defines structure.  
- All children must have an equal number of spaces.  
- Incorrect spacing causes a syntax error.  
Example of wrong indentation:  
banana:  
  calories: 105  
    fat: 0.4   # ❌ Wrong; extra spaces!  

* Nested Structures  

- YAML can contain lists inside dictionaries and dictionaries inside lists:  

Example:  
fruits:  
  - name: banana  
    nutrition:  
      calories: 105  
      carbs: 27  
  - name: grape  
    nutrition:  
      calories: 62  
      carbs: 16  

This shows:  
- A list of fruits, where each item is a dictionary and each dictionary contains another dictionary.  

* Key Rules to Remember  

- It uses indentation to define hierarchy.  
- No tabs, only spaces.  
- Consistent indentation is crucial.  
- It has a clean, human-readable format.







































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