Backing up docker wordpress containers created from the official image

In this short guide we'll learn how to back up a docker wordpress container that doesn't use Volumes, but keeps its data inside itself (something highly discouraged).

Let's take as an example a generic container created with the name nome-wordpress

This image will create an internal data volume /var/www/html/

To see the data of the attached volumes we need to use the inspect command:

docker inspect nome-wordpress

as you can see from the output, the data is in /var/www/html .

There are two phases: in the first one you save the docker container, in case special changes were made to it, php packages installed or ad hoc configurations.

To find the id you need to use docker ps -a

Then we'll commit the container locally, so we can then save it to an archive.

docker commit -p IDDELCONTAINER nome-wordpress:backup

nome-wordpress will be the name of the saved image, :backup will be the tag we're going to use

after that you save it to a file by running

docker save nome-wordpress:backup | gzip > nome-wordpress_backup.tar.gz

In the file nome-wordpress_backup.tar.gz we'll have the backup of the running container, but without data.

To save the data that's inside the container in /var/www/html/ you need to use a small helper container: busybox

Here are the parameters:

• $(pwd) means we map the current directory to the directory written after the : of the container
• /backups is the directory inside the busyboxy container
• —-rm is the parameter saying that after running the command tar -c /var/www/html -f /backups/html_nome-wordpress.tar the created container will be destroyed

docker run --rm -v $(pwd):/backups --volumes-from=nome-wordpress busybox tar -c /var/www/html -f /backups/html_nome-wordpress.tar

RESTORE ON ANOTHER MACHINE

The procedure here should be a bit simpler. Once you've copied over the two tars, the nome-wordpress container image and the data, you need to import them.

First of all we need to load the container image locally

docker load < nome-wordpress_backup.tar.gz

This way, running the command

docker images

We'll get an entry in the output with the name of the loaded image

# output

REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
nome-wordpress            backup              3915f4713629        About an hour ago   419 MB

We can then recreate and start the container from the image

docker run --name nome-wordpress-nuova-istanza -p 8080:80 -d nome-wordpress:backup

So, listing the running containers we'll get:

docker images

# output

CONTAINER ID        IMAGE                    COMMAND                  CREATED             STATUS              PORTS                  NAMES
874bca63408e        nome-wordpress:backup   "docker-entrypoint..."   25 seconds ago      Up 23 seconds       0.0.0.0:8080->80/tcp   nome-wordpress-nuova-istanza

This container will have all the service customizations and other configurations made previously, but not the data of the old site.

To import the data back we'll get some help from a busybox helper container like for the backup, where instead of running the save command, we'll run the extraction command tar -xvf /backups/html_nome-wordpress.tar -C / .

Let's assume we're in the same folder where we copied the two tars

docker run --rm -v $(pwd):/backups --volumes-from=nome-wordpress-nuova-istanza busybox tar -xvf /backups/html_nome-wordpress.tar -C /

And that's it, we've restored the container with the data included!