Docker packages software and its needs into a single unit that works on any computer. This ensures your code doesn't break when moving it from one person's machine to another.

The Universal Lunchbox Concept

An image is a read-only file that serves as a frozen template for your software. Think of it as a master blueprint used to build identical copies of an application.

Images as Master Blueprints

A container is a live, running version of an image. If the image is the blueprint, the container is the actual house where the software lives and breathes.

Containers as Active Workspaces

A Dockerfile is a simple text document containing a list of instructions. It tells Docker exactly which ingredients and steps are needed to build a specific image.

The Dockerfile Recipe Card

This is a giant online warehouse where people share pre-made images. You can download ready-to-use tools like databases or web servers from here in seconds.

Docker Hub Public Library

Pulling is the act of downloading an image from the internet to your local computer. It is very similar to downloading an app from a mobile app store.

Fetching with Docker Pull

This is the primary command used to turn an image into a working container. It starts the software so you can begin using it immediately.

Launching with Docker Run

Containers are isolated for safety, meaning they are locked away from your main computer. Port mapping opens a specific 'door' so you can access the app from your web browser.

Opening Doors with Ports

Standard containers forget everything once they are turned off. Volumes act like an external hard drive, allowing the software to save data permanently.

Permanent Memory with Volumes

Docker networking allows different containers to talk to each other securely. This is how a website container asks a database container for information.

Private Chat Between Apps

Tags are labels like 'v1' or 'latest' attached to images to track different versions. They help you choose between an older, stable version and a brand-new update.

Versioning with Image Tags

You can run containers in 'detached' mode so they stay active without taking up your screen. This allows the software to work quietly while you do other tasks.

Working in the Background

Docker allows you to see a live list of every container currently running on your system. This helps you monitor which apps are healthy and which have stopped.

Checking Your Active Apps

Old images and stopped containers can take up a lot of storage space. It is important to occasionally delete these unused items to keep your computer fast.

Tidying Up Your System

Images are built in layers, similar to a stack of transparent sheets. If you change one small part, Docker only updates that specific layer to save time and space.

The Problem: Memory Loss