Docker For Beginners

calendar Mar 25, 2025 · 3 min read · docker containerization devops programming development  ·
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You're building an app that works perfectly on your computer. But when you send it to your friend or deploy it on a server, it crashes. Sound familiar? 😩 In today’s fast-paced world of app development, consistency is everything. That’s where Docker comes in. Like a magic box 📦 that packs your app with everything it needs to run anywhere, without surprises. Docker has completely changed the game in how we develop, ship, and deploy applications using something called containerization.

What is Docker?

Docker is a tool that packages applications into containers, self-contained units that include:

  • Your application code
  • Dependencies (libraries, frameworks)
  • Configuration files

Think of Docker like a shipping container:

  • Standardizes deployment across environments
  • Runs identically on laptops, servers, or the cloud

Why Use Docker?

Benefit Description
Consistency No more works on my machine issues
Portability Run anywhere Docker is installed
Efficiency Lightweight (shares OS resources)
Scalability Spin up multiple containers in seconds
Isolation Apps run separately without conflicts

Containers vs. Virtual Machines

Docker Containers Virtual Machines (VMs)
🚀 Lightweight & fast 🐢 Heavier & slower
⚡ Shares host OS kernel 🔄 Requires full OS per VM
📦 Process-level isolation 🛡️ Hardware-level isolation
💾 Minimal resource usage 💽 High storage/memory consumption

Core Docker Components

  1. Image
    • Blueprint for containers (e.g., python:3.11-slim)
  2. Container
    • Running instance of an image
  3. Dockerfile
    • Recipe to build images (see example below)
  4. Docker Hub
    • Public registry for sharing images

Dockerfile Example

Dockerfiles are simple text files that define how to build Docker images. Here's an example Dockerfile for a Python app:

 1# Start from a base image
 2FROM python:3.11-slim
 3
 4# Set working directory
 5WORKDIR /app
 6
 7# Install dependencies
 8COPY requirements.txt .
 9RUN pip install -r requirements.txt
10
11# Copy app code
12COPY . .
13
14# Start command
15CMD ["python", "app.py"]

Basic Workflow

  1. Build Image 
    1docker build -t myapp .
  2. Run Container 
    1docker run -p 8000:8000 myapp
  3. Manage Containers 
    1docker ps      # List running containers
2docker stop <CONTAINER_ID>  # Stop a container
3docker rm <CONTAINER_ID>    # Delete a container

Essential Commands Cheatsheet

Command Description Example
docker build Build image docker build -t myapp .
docker run Start container docker run -d -p 8000:8000 myapp
docker ps List containers docker ps -a
docker images List images docker images
docker pull Download image docker pull ubuntu
docker exec Run command in container docker exec -it myapp bash

Real-World Use Case

Problem:
Your Python app works locally but crashes on your colleague's machine due to missing dependencies.

Docker Solution:

  1. Create a Dockerfile with Python + dependencies
  2. Build an image and share it
  3. Colleague runs the same container → identical environment!