New as of 0.5.0
The preferred method to mount external containers to a dokku managed container, is to use the dokku storage plugin.
storage:list <app>, List bind mounts for app's container(s) (host:container)
storage:mount <app> <host-dir:container-dir>, Create a new bind mount
storage:unmount <app> <host-dir:container-dir>, Remove an existing bind mountThe storage plugin requires explicit paths on the host side. This is intentional to ensure that new users avoid running into unexpected results with implicit paths that may not exist (a feature deprecate in Docker 1.9.0). The container directory is created for the mount point in the container. Any existing directory contents are not accessible after a mount is added to the container. Dokku creates a new directory /var/lib/dokku/data/storage during installation, it's the general consensus that new users should use this directory. Mounts are only available at run and deploy times, you must redeploy (restart) an app to mount or unmount to an existing app's container.
This example demonstrates how to mount the recommended directory to /storage inside the container:
$ dokku storage:mount app-name /var/lib/dokku/data/storage:/storage
Dokku will then mount the shared contents of/var/lib/dokku/data/storage to /storage inside the container.
Dokku is powered by Docker containers, which recommends in their best practices that containers be treated as ephemeral. In order to manage persistent storage for web applications, like user uploads or large binary assets like images, a directory outside the container should be mounted.
When scaling your app, you may require a common location to access shared assets between containers, a storage mount can be used in this situation.
Your app may be used in a cluster that requires containers or resources not running on the same host access your data. Mounting a shared file service (like S3FS or EFS) inside your container will give you great flexibility.
Your app may have services that are running in memory and need to be backed up locally (like a key store). Mount a non ephemeral storage mount will allow backups that are not lost when the app is shut down.
The storage plugins is compatible with storage mounts created with the docker-options. The storage plugin will only list mounts from the deploy phase.