The problem Docker solves

The problem Docker solves

Without containers, a developer machine accumulates SDKs, database servers, Redis, RabbitMQ, Node versions, and OS-level dependencies. Two developers can run the same code and get different results because their machines differ. Docker moves most of that environment into versioned artifacts.

Without Docker vs with Docker

The lifecycle you should memorize

1. Get/build an image

docker pull nginx:alpine
# or
docker build -t my-api:1.0 .

2. Create + start a container from the image

docker run -d --name my-api -p 8080:8080 my-api:1.0

3. Observe/debug it

docker ps
docker logs -f my-api
docker inspect my-api

4. Stop/start the same container

docker stop my-api
docker start my-api

5. Remove the container

docker rm -f my-api

Containers vs virtual machines

A virtual machine virtualizes hardware and normally runs a complete guest operating system with its own kernel. A Linux container isolates processes using Linux kernel features while sharing the container host's kernel. That is why containers usually start faster and consume less overhead than full VMs.

Windows nuance: Linux containers on Windows do not share the Windows kernel. Docker Desktop commonly uses a WSL 2 based Linux environment under the hood. Your containers still see a Linux kernel even though you launch docker commands from PowerShell.

Core Docker vocabulary