Docker Concepts That Will Break Your Brain (Until You Get Them!)

Why is it that Docker makes total sense… until it doesn’t?

You build an image, run a container, and everything seems fine – until you restart it and poof your data is gone.

Or worse, your container runs on your machine but fails in production.

I’ve been there – staring at a terminal, questioning why a simple docker run isn’t doing what I expected.

Docker is amazing, but there are some tricky concepts that trip up even experienced engineers.

Let’s break them down in plain English.

1️⃣ Docker Image vs. Container (Not the Same Thing!)

At first, they seem interchangeable, but they’re completely different.

📍Image → The blueprint (read-only), like an ISO file for a VM.

📍Container → A running instance of an image. It’s like a VM created from an ISO.

🔸Tricky part? If you modify a running container, those changes disappear when the container stops – unless you commit them to a new image.

📌 Pro Tip: Treat containers as disposable. Build new images instead of modifying running containers.

2️⃣ Why Does My Data Disappear? (Volumes vs. Bind Mounts)

You start a container, add some data, restart it… and everything’s gone.