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Persistent Storage

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:report [<app>] [<flag>]                # Displays a checks report for one or more apps
storage:unmount <app> <host-dir:container-dir> # Remove an existing bind mount

The storage plugin is compatible with storage mounts created with the docker-options. The storage plugin will only list mounts from the deploy/run phase.

The storage plugin supports the following mount points:

  • explicit paths that exist on the host
  • docker volumes

There are a few caveats to using the persistent storage plugin:

  • Using implicit paths that do not exist are no longer supported, and actually deprecated in Docker 1.9.0. When you specify a persistent storage mount, the host directory is not autocreated by either Dokku or Docker.
  • We recommend using the directory /var/lib/dokku/data/storage directory as the root host path for mounts, and we create this on Dokku installation.
  • Mounts are only available at run and deploy times, and you must redeploy (restart) an app to mount or unmount to an existing app's container.
  • When a directory is mounted, any existing files within the container will be overwritten. If you are writing assets during the build process and then replace the directory with a mount, those files will no longer exist. This is a Docker limitation.
  • Paths are mounted within the container at the root of the disk - / - and are not relative to /app (for buildpacks deploys) or the WORKDIR (for Dockerfile/Docker images).
  • For applications using buildpack deploys, the host directory should be owned by the user and group id 32767. This is due to how permissions within Herokuish - which builds the Docker images - works. For Dockerfile or Docker image deployments, please use the user and group id which corresponds to the one running the process within the container.

Usage

This example demonstrates how to mount the recommended directory to /storage inside an application called node-js-app:

# we use a subdirectory inside of the host directory to scope it to just the app
dokku storage:mount node-js-app /var/lib/dokku/data/storage/node-js-app:/storage

Dokku will then mount the shared contents of /var/lib/dokku/data/storage to /storage inside the container.

Once you have mounted persistent storage, you will also need to restart the application. See the process scaling documentation for more information.

dokku ps:rebuild app-name

A more complete workflow may require making a custom directory for your application and mounting it within your /app/storage directory instead. The mount point is not relative to your application's working directory, and is instead relative to the root of the container.

# creating storage for the app 'node-js-app'
mkdir -p  /var/lib/dokku/data/storage/node-js-app

# ensure the proper user has access to this directory
chown -R dokku:dokku /var/lib/dokku/data/storage/node-js-app

# as of 0.7.x, you should chown using the `32767` user and group id for buildpack deploys
# For dockerfile deploys, substitute the user and group id in use within the image
chown -R 32767:32767 /var/lib/dokku/data/storage/node-js-app

# mount the directory into your container's /app/storage directory, relative to root
dokku storage:mount app-name /var/lib/dokku/data/storage/node-js-app:/app/storage

You can mount one or more directories as desired by following the above pattern.

Displaying storage reports about an app

New as of 0.8.1

You can get a report about the app's storage status using the storage:report command:

dokku storage:report
=====> node-js-app storage information
       Storage build mounts:
       Storage deploy mounts: -v /var/lib/dokku/data/storage/node-js-app:/app/storage
       Storage run mounts:  -v /var/lib/dokku/data/storage/node-js-app:/app/storage
=====> python-sample storage information
       Storage build mounts:
       Storage deploy mounts:
       Storage run mounts:
=====> ruby-sample storage information
       Storage build mounts:
       Storage deploy mounts:
       Storage run mounts:

You can run the command for a specific app also.

dokku storage:report node-js-app
=====> node-js-app storage information
       Storage build mounts:
       Storage deploy mounts: -v /var/lib/dokku/data/storage/node-js-app:/app/storage
       Storage run mounts:  -v /var/lib/dokku/data/storage/node-js-app:/app/storage

You can pass flags which will output only the value of the specific information you want. For example:

dokku storage:report node-js-app --storage-deploy-mounts

Use Cases

Persistent storage

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.

Shared storage between containers

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.

Shared storage across environments

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.

Backing up

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.

Build phase

By default, Dokku will only bind storage mounts during the deploy and run phases. Under certain conditions, one might want to bind a storage mount during the build phase. This can be accomplished by using the docker-options plugin directly.

dokku docker-options:add <app> build "-v /tmp/python-test:/opt/test"

You cannot use mounted volumes during the build phase of a Dockerfile deploy. This is because Docker does not support volumes when executing docker build.

Note: This can cause data loss if you bind a mount under /app in buildpack apps as herokuish will attempt to remove the original app path during the build phase.

Application User and Persistent Storage file ownership (buildpack apps only)

New as of 0.7.1

By default, Dokku will execute your buildpack application processes as the herokuishuser user. You may override this by setting the DOKKU_APP_USER config variable.

NOTE: this user must exist in your herokuish image.

Additionally, Dokku will ensure your storage mounts are owned by either herokuishuser or the overridden value you have set in DOKKU_APP_USER.

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