Hello world in Docker
In a previous post, we saw how to install Docker and, at the same time, run the first "hello-world" container. However, this first example might be somewhat confusing for someone just starting with Docker. For this reason, today we will look at a slightly different "Hello World" that better represents the essence of Docker.
In this example, we will use a Dockerfile as it is the most common way you will see in a professional environment to run a Docker container based on an image.
Create the Dockerfile
Every container in docker starts with a Dockerfile which defines what happens inside the container's environment. You must create a folder for this project and within this folder you must create the Dockerfile file and paste the following content in it.
FROM httpd:2.4
COPY ./html/ /usr/local/apache2/htdocs/
As you can see it is extremely simple, the first line of this file tells us that the container will be an instance of the httpd:2.4 image, which comes with apache installed. The third line copies everything we have in the html folder to /usr/local/apache2/htdocs. To make this work correctly you will also need to create the html folder in the project directory. Finally our hello world will go in the index.html file inside this last folder.
mkdir html
echo "<h2>Hello world</h2>" > html/index.htmlCreate the image
We need to create our own image that will be based of course on httpd as specified in our Dockerfile. To do this, we must run the following command:
docker build --tag=holamundo .The parameter in --tag refers to the name that will be given to our image.
Run an instance
The last thing that remains is to run an instance of our image, that is, to create a container. For this, we are going to map port 80 of the container to port 8080 of our computer.
docker run -p 8080:80 holamundoIf everything has gone well we could access the URL http://0.0.0.0:8080/ and see a Hello world as a result in the browser.
Finally, I leave you with these two basic docker commands that will help you to know what images and containers exist on your host.
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
holamundo latest eb11397e547a 30 minutes ago 154MB
$ docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
f54c000c919d holamundo "httpd-foreground" 33 minutes ago Up 33 minutes 0.0.0.0:8081->80/tcp hardcore_lamport
Until next time!