Write Your First Dockerfile

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Your first Dockerfile Step by Step

Let’s create this Dockerfile:

FROM php:7.2-cli

RUN mkdir /myproject
COPY index.php /myproject
WORKDIR /myproject
CMD php index.php

It take a “php:7.2-cli” base image, and then adds a few things on top:

• makes a new directory /myproject”
• copies index.php into /myproject
• makes the workdir /myproject, meaning, the container will start in this directory (like cd /myproject)
• when the container starts it will run php index.php

And also this index.php file in the same directory:

<?php
 
echo "hello world \n\n";
 

Now go into the folder where the Dockerfile is located at. And open in a terminal type:

docker build -t myphpapp .

But what does it do?

• build builds a new image
• -t is a tagging. In this case “myphpapp”, so you can later find it.
• . is telling Docker what is the “build context”. Meaning, in the Dockerfile you wrote COPY index.php /myproject, that means it knows to look in this folder when searching for this index.php file

Then run the container:

docker run --name myphpapp myphpapp

• Should print out “hello world” with two line breaks
• Ends the container immediately, the process “php index.php” has finished
• “CMD php index.php” opens this upon spin up of the container
• Give the container a name called “myphpapp”

docker image ls

• List all the images
• See on top your newly created image

docker ps -a

• List the containers

docker rm myphpapp

• Remove the container

docker rmi myphpapp

• rm i will delete an image
• And all depending images if they are not necessary anymore