Kubernetes Deployments Guide

This repository provides a simple guide and example commands to help you understand and work with Kubernetes Deployments, DaemonSets, and StatefulSets.

Overview

Deployments

Deployments are used by 99.99% of people to deploy their applications. They include ReplicaSets and Pods.

DaemonSets

DaemonSets ensure that a pod is run on each node in the cluster. This is typically used for log collection and monitoring.

StatefulSets

StatefulSets maintain the identity of pods, ensuring the hostname remains the same, which is crucial for stateful applications like MongoDB and MySQL.

Commands Used

Creating a Deployment

kubectl create deployment testapp --image kiran2361993/kubegame:v1 --replicas 3 --dry-run -o yaml

Adding Another Container

Add the following container to the deployment:

• Image: kiran2361993/mydb:v1
• Name: Database

Labels and Annotations

Labels are key-value pairs used to pass information.

Creating Pods

kubectl run testpod1 --image nginx:latest

Deploying the Deployment

kubectl apply -f deployment.yaml
kubectl get pods

Adding Annotations

Annotations can pass information such as:

• Info: "This Deployment file has been created by Saikiran Pinapathruni"
• Email: "[email protected]"
• Owner: "Saikiran Pinapathruni"

Environment Variables

Set environment variables at the container level:

env:
  - name: DB_NAME
    value: "mysqldb"
  - name: DB_PORT
    value: "3306"
  - name: DB_URL
    value: "saikiranpi.in/mydb"

Checking Environment Variables

kubectl describe pod <podname>
kubectl exec -it <podname> -- bash
env

Exposing the Deployment

kubectl expose deployment testapp --name sv1 --port 8000 --target-port 80 --type NodePort
kubectl expose deployment testapp --name sv2 --port 5000 --target-port 5000 --type NodePort

Strategy

kubectl explain deployment.spec.strategy

Under spec:

strategy:
  rollingUpdate:
    maxSurge: 1
    maxUnavailable: 0%

Deployment Update Strategy

kubectl edit deployment testapp

Under spec:

minReadySeconds: 10
maxUnavailable: 0

DaemonSets and StatefulSets

DaemonSets

DaemonSets ensure that one pod is run on each node.

StatefulSets

StatefulSets maintain the identity of pods, ensuring the hostname remains the same.

Interview Questions

What is the difference between Deployments, DaemonSets, and StatefulSets?

• Deployments: Used for stateless applications, allowing for scaling up and down without dependencies on pod names.
• DaemonSets: Ensure one pod per node, typically used for log collection and monitoring.
• StatefulSets: Maintain pod identity, crucial for stateful applications like databases.