You have multiple ways to enable data persistence with docker

In this light tutorial we will cover the two most used possibilities.

  • Data persistence with a folder linked between the host and the container

  • Data persistence with the cmd docker volume

Install Docker (on debian distro)

Install docker @art-dambrine docker @ubuntu-fr.org

Start and test a container

We will take a webserver as an exemple.

docker run -dit --name my-apache-test -p 8081:80 httpd:2.4
Note
 make sure that port 8081 is available on your host

You will see your web server welcome page if you connect to your-ip:8081

Now let’s try to modify data inside the container

docker exec -ti my-apache-test bash
Note
 we use docker exec -ti with cmd bash to enter the container file system

We install nano on the container with nano to test modifying index.html

cd /usr/local/apache2/htdocs
apt update && apt install nano
nano index.html

We can see that if we restart the container our modifications are still here. However, now if I delete my container, I will lose my data :

docker stop my-apache-test
docker rm my-apache-test

If we run our container again with the above cmd docker run -dit --name my-apache-test -p 8081:80 httpd:2.4 we will see a fresh new container without our modified datas.

How to make data persitant

1 - With -v argument and path to persistent folder

docker run -dit -p 8081:80 -v /home/art/docker-test/html:/usr/local/apache2/htdocs --name my-apache-test httpd:2.4

From my host machine or from my container console, I can now add persistent content to html folder

cd /home/art/docker-test/html
echo 'Hello world!' > index.html
docker exec -ti my-apache-test bash
cd /usr/local/apache2/htdocs
echo '<br>Test from the container' >> index.html

2 - With docker volume

You can use docker volume to create and administrate docker volumes

docker volume create myvolume

If you want to know where your volume is stored (and other informations)

docker volume inspect myvolume

Let’s launch a web container with this volume mounted

docker run -dit --name httpd-container -p 8081:80 --mount source=myvolume,target=/usr/local/apache2/htdocs httpd:2.4

To edit the data inside the container we need to inside it or edit the volume from the host machine.

Let’s edit from the host machine (more specific)

To know where our volume is stored :

docker volume inspect myvolume
sudo su
cd /var/lib/docker/volumes/myvolume/_data
nano index.html
Note
 To edit from the host you need now to be root (it’s not common to do so by the way - we do it for testing purpose)

Now we can launch any container with this volume mounted

docker run -dit --name nginx-container -p 8082:80 --mount source=myvolume,target=/usr/share/nginx/html nginx:stable
Note
 If you go to your-ip:8082 you will find your same index.html but this time served by nginx 🔥🔥🔥