Docker ships with its own “Hello, World” image that is a helpful first step to run. Open your terminal and On the command line type docker run hello-world. This will download an official Docker image and then run it within a container. We’ll discuss both images and containers in a moment.

Command Line

$ docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
1b930d010525: Pull complete
Digest: sha256:b8ba256769a0ac28dd126d584e0a2011cd2877f3f76e093a7ae560f2a5301c00
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.(amd64)
3. The Docker daemon created a new container from that image which runs the executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it to your terminal.
To try something more ambitious, you can run an Ubuntu container with:
$ docker run -it ubuntu bash
Share images, automate workflows, and more with a free Docker ID:
https://hub.docker.com/
For more examples and ideas, visit:
https://docs.docker.com/get-started/

The command docker info lets us inspect Docker. It will contain a lot of output but focus on the top lines which show we now have 1 container which is stopped and 1 image.

This means Docker is successfully installed and running.

Images, Containers, and the Docker Host
A Docker image is a snapshot in time of what a project contains. It is represented by a Dockerfile and is literally a list of instructions that must be built.

A Docker container is a running instance of an image.

“Docker host” is the underlying OS.

It’s possible to have multiple containers running within a single Docker host. When we refer to code or processes running within Docker, that means they are running in the Docker host.
To create a dockerfile we run the command:

$ touch Dockerfile

Docker containers are, by their nature, ephemeral. They only exist when being run and all data within them is deleted when the container stops. We work around this by using volumes for persistent data. Within the web service we already have a volume that links our local code to the running container and vice versa.