DevOps Sample codes for Interview Preparation

1. Dockerfile Example

A basic Dockerfile for a Python application:

FROM ubuntu:20.04

# Set environment variables
ENV APP_HOME /app

# Create app directory
WORKDIR $APP_HOME

# Install dependencies
RUN apt-get update && apt-get install -y \
    python3 \
    python3-pip \
    && rm -rf /var/lib/apt/lists/*

# Copy application files
COPY . .

# Install Python dependencies
RUN pip3 install -r requirements.txt

# Expose port
EXPOSE 5000

# Command to run the application
CMD ["python3", "app.py"]

2. Docker Compose Example

A simple docker-compose.yml file for a web application with database:

version: '3'

services:
  app:
    build: .
    ports:
      - "5000:5000"
    volumes:
      - ./:/app
    environment:
      - DB_HOST=db
      - DB_NAME=mydb
      - DB_USER=user
      - DB_PASSWORD=password
    depends_on:
      - db
  
  db:
    image: postgres:13
    ports:
      - "5432:5432"
    environment:
      - POSTGRES_DB=mydb
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=password
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

3. Jenkinsfile Example

A basic Jenkins pipeline with build, test, and deploy stages:

pipeline {
    agent any
    
    stages {
        stage('Build') {
            steps {
                echo 'Building the application...'
                sh 'docker build -t myapp:latest .'
            }
        }
        
        stage('Test') {
            steps {
                echo 'Running tests...'
                sh 'docker run myapp:latest python3 -m unittest'
            }
        }
        
        stage('Deploy') {
            steps {
                echo 'Deploying the application...'
                sh 'docker-compose up -d'
            }
        }
    }
    
    post {
        success {
            echo 'Pipeline completed successfully!'
        }
        failure {
            echo 'Pipeline failed!'
        }
    }
}

4. GitLab CI Configuration Example

A simple .gitlab-ci.yml file with build, test, and deploy stages:

stages:
  - build
  - test
  - deploy

build:
  stage: build
  script:
    - echo "Building the application..."
    - docker build -t myapp:latest .
  tags:
    - docker

test:
  stage: test
  script:
    - echo "Running tests..."
    - docker run myapp:latest python3 -m unittest
  tags:
    - docker

deploy:
  stage: deploy
  script:
    - echo "Deploying to production..."
    - docker-compose up -d
  only:
    - main
  tags:
    - docker

5. Terraform Example

A basic Terraform configuration to list VPC and EC2 instances:

# Provider configuration
provider "aws" {
  region = "us-east-1"
}

# Data source to get all VPCs
data "aws_vpcs" "all_vpcs" {}

# Data source to get all EC2 instances
data "aws_instances" "all_instances" {}

# Output VPC IDs
output "vpc_ids" {
  value = data.aws_vpcs.all_vpcs.ids
}

# Output EC2 Instance IDs
output "instance_ids" {
  value = data.aws_instances.all_instances.ids
}

# Output EC2 Instance details
output "instance_details" {
  value = [
    for instance in data.aws_instances.all_instances.instances :
    {
      id        = instance.id
      type      = instance.instance_type
      state     = instance.state
      private_ip = instance.private_ip
    }
  ]
}

6. Bash Script Example

A basic bash script for server health monitoring:

#!/bin/bash

# Basic Server Health Check Script

echo "========== Server Health Check =========="
echo "Date: $(date)"
echo ""

# Check disk space
echo "--- Disk Space ---"
df -h | grep -vE '^Filesystem|tmpfs|cdrom'
echo ""

# Check memory usage
echo "--- Memory Usage ---"
free -m
echo ""

# Check CPU load
echo "--- CPU Load ---"
uptime
echo ""

# Check active processes
echo "--- Top 5 CPU-consuming processes ---"
ps aux --sort=-%cpu | head -6
echo ""

# Check system uptime
echo "--- System Uptime ---"
uptime -p
echo ""

echo "========== End of Health Check =========="