What Are Containers?
Containers are isolated environments for running applications. Unlike virtual machines, containers don't include a full operating system — they share the host's kernel while keeping everything else separate. This makes them lightweight, fast, and incredibly useful for developers.
The "Works on My Machine" Problem
Every developer has experienced this frustration: code works perfectly on your computer but fails on someone else's. Different software versions, missing dependencies, conflicting configurations — countless things can go wrong when environments don't match.
Containers solve this by packaging your application with everything it needs: code, libraries, configuration files, and dependencies. The container runs identically whether it's on your laptop, a colleague's machine, or a production server.
Think of containers like shipping containers. Before standardized containers, loading cargo onto ships was chaotic — different sizes, shapes, and handling requirements. Shipping containers standardized everything. Pack once, ship anywhere. Software containers work the same way.
How Containers Differ from VMs
| Aspect | Virtual Machine | Container |
|---|---|---|
| Size | Gigabytes | Megabytes |
| Startup | Minutes | Seconds |
| Isolation | Complete OS | Shared kernel |
| Use case | Different OS needed | Consistent app environments |
VMs are like separate houses — each with its own foundation, plumbing, and electrical system. Containers are like apartments — private spaces sharing building infrastructure.
Docker: The Container Standard
Docker is the most popular container platform. Key concepts:
- Image — A blueprint defining what's in the container
- Container — A running instance of an image
- Registry — A place to store and share images
You'll use containers extensively in later tracks to run databases, set up development environments, and deploy applications.
Why This Matters
Containers keep your system clean. Instead of installing databases, language runtimes, and tools directly on your computer, you run them in containers. Each project gets exactly what it needs without cluttering your system or conflicting with other projects.