Docker Basics - System Commands

What is YAML?

YAML (YAML Ain't Markup Language) is a human-readable data serialization language. It's commonly used for configuration files and in applications where data is being stored or transmitted. Docker uses YAML for Docker Compose files.

YAML Basics:

Uses indentation to represent structure (spaces, not tabs)
Case sensitive
File extension is typically .yml or .yaml
Supports comments starting with #
Uses key-value pairs separated by a colon

Basic YAML Structure

name: "John Doe"
age: 30
is_student: false
hobbies:
  - "reading"
  - "hiking"
  - "coding"
address:
  street: "123 Main St"
  city: "Anytown"
  zip: 12345

Explanation:

Key-value pairs separated by colons
Lists (arrays) are represented with hyphens
Nested objects use indentation
Strings can be quoted or unquoted

Docker Compose Example

# Docker Compose file version
version: '3.8'

# Define services (containers)
services:
  # Web service using nginx
  web:
    image: nginx:latest
    ports:
      - "80:80"
    volumes:
      - ./html:/usr/share/nginx/html

  # Database service using PostgreSQL
  database:
    image: postgres:13
    environment:
      POSTGRES_DB: "mydb"
      POSTGRES_USER: "user"
      POSTGRES_PASSWORD: "password"
    volumes:
      - db_data:/var/lib/postgresql/data

# Define volumes
volumes:
  db_data:

Explanation:

Defines multiple services that work together
Specifies container images and configurations
Maps ports between host and containers
Sets environment variables
Defines volumes for data persistence

Dockerfile Basics

A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using docker build, users can create an automated build that executes several command-line instructions in succession.

Sample Dockerfile for Node.js Application:

# Use an official Node.js runtime as a base image
FROM node:18-alpine

# Set the working directory in the container
WORKDIR /app

# Copy package.json and package-lock.json (if available)
COPY package*.json ./

# Install dependencies
RUN npm install

# Copy the rest of the application code
COPY . .

# Make port 3000 available to the world outside this container
EXPOSE 3000

# Define environment variable
ENV NODE_ENV=production

# Run the application when the container launches
CMD ["npm", "start"]

Common Dockerfile Instructions:

FROM → Sets the base image
RUN → Executes commands
COPY → Copies files from host to container
WORKDIR → Sets the working directory
EXPOSE → Documents which ports the container uses
CMD → Provides default command for container

Building and Running:

docker build -t my-node-app .

docker run -p 4000:3000 my-node-app