The Docker Tutorial

I found this interesting tutorial on Laracasts. It's by Andrew Schmelyun.

Episode 1 - What is Docker

Docker is a software platform that uses containers to build, share and run applications.
You can use Docker Desktop.
Alternatively, you can follow these steps Install Docker Engine on Ubuntu and Install Docker Compose.

Now Docker is installed. How can we use it?
First we open a terminal and enter the following command:

docker run hello-world

The command pull down the "hello-world" container from the docker hub.
To remove the container completely just use the following command:

docker run --rm hello-world

or delete it using the delete icon in the Docker desktop application.

To get version information about the pulled container just use the following command:

docker run --rm ubuntu:latest cat /etc/os-release

Episode 2 - Create a Simple Docker File

First we create a custom Dockerfile:

touch Dockerfile
code Dockerfile

The aim of this file is to provide us a set of instructions for docker to use that builds and prepares our container when we use docker run.
Lets think of something we can do with this container. How about to create a container for a JSON Server.

The first thing that has to be included in every Dockerfile is the "FROM" command:

FROM node:latest

This is followed by the base image that you want to build your container.

Next we use the "WORKDIR" command to determine in what directory we are going to be in when we run any following commands:

WORKDIR /home/server

If the directory isnt available it will be created.

To execute instructions like installing a npm package we can use the "RUN" command:

RUN npm install -g json-server

For the JSON Server we need a file for its data:

touch db.json
code db.json

with the following example data:

{
  "posts": [
    {
      "title": "My first Post",
      "author": "web devapps"
    },
    {
      "title": "My second Post",
      "author": "web devapps"
    }
  ],
  "profile": {
    "first_name": "Web",
    "last_name": "Devapps",
    "email": "ich@webdevapps.de"
  }
}

In order to be able to use the data file in our Docker container we can use the "COPY" command to copy the file into the container:

COPY db.json /home/server/db.json

The last thing we need to do is tell Docker to actually run json-server. There are two ways to do it:

1. "ENTRYPOINT"
2. "CMD"

"ENTRYPOINT" is the main command ran by the Docker container. It can not be overwritten by commands on the host machine instead commands are added to it.

"CMD" is for additional commands or options that will run after the "ENTRYPOINT" command.

For now we use the "ENTRYPOINT" command:

ENTRYPOINT ["json-server", "db.json"]

There is also the alternative shell form:

ENTRYPOINT /bin/sh -c json-server db.json

But we use the exact form as array notation above.

Now its time to build the container:

docker build .

After the Docker container has been created, we can display the docker images with:

docker image list