Summary - What is Docker

Combine Docker's core concepts to write a container definition.

Summary: what Docker is

In this group:

Docker runs an application with its dependencies inside a container.
A container shares the host kernel; it is lighter and faster than a VM, and its isolation comes from namespaces and cgroups.
An image is a read-only template; a container is its running instance and carries its own writable layer.
The CLI sends commands to the daemon; the daemon pulls images from the registry.
One-off tools can be run with --rm.

docker pull nginx
docker run -d --name web --memory 256m nginx
docker run --rm alpine echo merhaba

Exercise All together

Write three commands: pull the alpine image; start a container from it that runs echo merhaba and is deleted when done; finally start a container named web from the nginx image running in the background.

Show example solution

docker pull alpine
docker run --rm alpine echo merhaba
docker run -d --name web nginx

Test yourself

What happens to a file created inside a container when the container is removed?
- It is deleted together with the writable layer
- It is saved into the image
- It is uploaded to Docker Hub
- It is moved to the host desktop
Show answer

It is deleted together with the writable layer — Persistent data needs a volume.

Start the container in the background.

docker run ____ --name web nginx

Show answer

docker run -d --name web nginx

Match.

image

Template
container

Instance
dockerd

Daemon
--rm

Automatic removal

Next lesson: Installing Docker

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