What is Docker?

Learn that Docker is a container-based platform and why it is used.

What is Docker?

Docker is a platform that runs an application together with everything it needs (libraries, runtime, configuration files) in an isolated package called a container. This removes the "it worked on my machine" problem: the same container behaves the same on the developer's laptop, on the test server and in the cloud.

docker run nginx      # runs the nginx web server with one command

The first command

On a machine with Docker installed, the first try is usually the hello-world image. If Docker can't find the image locally it downloads it from Docker Hub, creates a container, runs it, and the container stops once its work is done:

$ docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
Hello from Docker!
This message shows that your installation appears to be working correctly.

This single command does all the steps of downloading, creating and running.

Exercise Hello Docker

Write the command that runs a container from the hello-world image.

Test yourself

What is the main problem Docker solves?
- Browser incompatibilities
- An application not running the same way in every environment
- Code compiling slowly
- Slow database queries
Show answer

An application not running the same way in every environment — A container packages the application with its dependencies; environment differences disappear.

Run a container from an image.

docker ____ hello-world

Show answer

docker run hello-world

Match the concepts.

Docker

Container platform
container

Isolated running process
Docker Hub

Public image repository
hello-world

Installation test image

Next lesson: Containers and virtual machines

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