Getting Started with OpenShift

Chapter 8. Disk Usage

Almost all applications want to either read or store files directly on the servers they are hosted upon. These files could be images, text files, documents, or the files that the database uses to store the data. Sometimes you (or your application) just need a temporary space to output a file or store a file before processing. When you move to “the cloud,” file storage has different properties than storing files on your laptop or even your own server in a rack. OpenShift has ways of handling all these application needs.

Where You Can Write “to Disk”

As an OpenShift application developer, you are given specific locations on “disk” where you are allowed to create or modify files and directories. We use disk in quotes because, as a developer, you are not actually sure what the space is located on—it could be disk drives, solid state drives, a network-attached storage (NAS) device, or any other storage location. As a developer, there are only two locations you should write files: /tmp and the gear’s data directory.

As on all Linux systems, you have read, write, and execute permissions for the /tmp directory. However, unlike a typical Linux machine, where everyone on the machine shares those permissions on /tmp, OpenShift uses pluggable authentication module (PAM) namespaces to give you your very own /tmp. This means nobody else on the machine can see or use the /tmp that you use. The problem with putting files here is that the space is ephemeral, ...