How Can I Backup a Docker-Container with Its Data-Volumes?

if I want to revert the container I can try to commit an image, and then later delete the container, and create a new container from the committed image. But if I do that the volume gets deleted and all my data is gone

As the docker user guide explains, data volumes are meant to persist data outside of a container filesystem. This also ease the sharing of data between multiple containers.

While Docker will never delete data in volumes (unless you delete the associated container with docker rm -v), volumes that are not referenced by any docker container are called dangling volumes. Those dangling volumes are difficult to get rid of and difficult to access.

This means that as soon as the last container using a volume is deleted, the data volume becomes dangling and its content difficult to access.

In order to prevent those dangling volumes, the trick is to create an additional docker container using the data volume you want to persist so that there will always be at least that docker container referencing the volume. This way you can delete the docker container running the wordpress app without losing the ease of access to that data volume content.

Such containers are called data volume containers.

There must be some simple way to back up my container plus volume data but I can't find it anywhere.

backup docker images

To backup docker images, use the docker save command that will produce a tar archive that can be used later on to create a new docker image with the docker load command.