What the Heck is Docker?

"What's Docker? What's a container? What's an image? Bla bla bla..." These are the questions my colleagues always ask me when they start learning Docker. And, to be honest, I asked the same questions when I was first introduced to it.

But you know what? Answers like, "Docker is a platform where..." didn’t really satisfy me. Sure, those answers are correct, but they didn't help me understand Docker. I had deeper questions like:

• Why should I use Docker?
• What’s containerization exactly?
• How is it different from virtualization?

If you’re like me, these are the questions that matter. So, let’s break it down together.

Is "What’s Docker?" the Right Question?

Yes, it’s a valid question. But here’s the catch: the answer to "What’s Docker?" is just the tip of the iceberg. If you ask someone this, they’ll probably say:

"Docker is a platform for developing, shipping, and running applications in containers."

Cool, but... what does that even mean?

To really understand Docker, you need to ask a better question: "What is containerization?"

What’s Containerization?

Here’s a textbook definition:

"Containerization is the process of packaging an application, along with its dependencies (libraries, configuration files, and binaries), into a lightweight, portable, and consistent unit called a container."

Sounds fancy, right? But does it really help you visualize what containerization is? Probably not. Let’s dig deeper.

Concepts You Need to Know to Understand Containerization

Before approaching containerization, you need to understand some core concepts. Without these, Docker and containers might feel like magic. Here’s what you should explore first:

1. The Software Deployment Process Think about how applications are traditionally deployed. In the "pre-container" world:
   • You write code on your local machine.
   • Then, you configure it to work on a server.
   • But wait! The server needs specific versions of libraries, dependencies, and tools to run your app.
   • Uh-oh, it works on your local machine but crashes in production because the environments aren’t identical.

This is the classic "It works on my machine!" problem. Containerization solves this by ensuring that your application and its dependencies are bundled into a single, portable unit (the container) that can run anywhere.

1. Virtualization
   
   To understand containers, you need to understand how virtualization works:

   • Virtual Machines (VMs): These are like mini-computers running inside your actual computer. They emulate an entire operating system (OS) and are great for isolating applications.
   • Containers: Unlike VMs, containers don’t emulate an entire OS. Instead, they share the host OS's kernel while isolating your application and its dependencies. This makes containers much lighter and faster than VMs.

2. Containerization
   
   Now that you understand virtualization( of course just a tip of it, dig deep into it for more understanding), you can appreciate what containerization does:

   • It isolates your application, just like a VM.
   • It’s lightweight and portable, unlike a VM.
   • It ensures consistency across development, staging, and production environments.

How Docker Fits Into the Picture

Docker is the tool that makes containerization easy. It provides:

• A way to create containers (using Docker images).
• A way to share containers (via Docker Hub or private registries).
• A way to run containers (on your local machine, servers, or even in the cloud).

So in simple terms: Docker makes containerization accessible to everyone.

If you want to understand Docker, start by understanding containerization. And if you want to understand containerization, take some time to learn about software deployment and virtualization first. Once you’ve got the basics down, Docker (and all its buzzwords like "containers" and "images") will start to make sense.

Resources that helped me

I couldn't remember all the resources that helped me, but here are some of them(None of the links are affiliated):

• A course on Edx: Introduction to containers, Kubernets and OpenShift
• Fireship (YouTube) - Docker 101

Thanks for reading!