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Persistent volumes for Docker containers
Solid Bodies
Docker guarantees the same environment on all target systems: If the Docker container runs for the author, it also runs for the user and can even be preconfigured accordingly. Although Docker containers seem like a better alternative to the package management of current distributions (i.e., RPM and dpkg), the design assumptions underlying Docker and the containers distributed by Docker differ fundamentally from classic virtualization. One big difference is that a Docker container does not have persistent storage out of the box: If you delete a container, all data contained in it is lost.
Fortunately, Docker offers a solution to this problem: A volume service can provide a container with persistent storage. The volume service is merely an API that uses functions in the loaded Docker plugins. For many types of storage, plugins allow containers to be connected directly to a specific storage technology. In this article, I first explain the basic intent of persistent memory in Docker and why a detour through the volume service is necessary. Then, in two types of environments – OpenStack and VMware – I show how persistent memory can be used in Docker with the appropriate plugins.
Planned Without Storage
The reason persistent storage is not automatically included with the delivery of every Docker container goes back to the time long before Docker itself existed. The cloud is to blame: It made the idea of permanent storage obsolete because storage regularly poses a challenge in classic virtualization setups. If you compare classic virtualization and the cloud, it quickly becomes clear that two worlds collide here. A virtual machine (VM) in a classic environment rightly assumes that it is on persistent storage, so the entire VM can be moved from one host to another. However, this requires redundant memory in the background on which the data is stored centrally. Local memory (e.g., on the hard
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