Last updated 26th March 2021


The built file system image that results from your build process is mounted read-only. That means it cannot be edited in production, even by accident.

Many applications still require the ability to write and store files, however. For that, applications can specify one or more mount points, that is, directories that will be mounted from a writable network file system cluster. They may be mounted anywhere within the file system of your application. If the specified directory already exists the contents of it will be masked by the writable mount and inaccessible at runtime.


Your plan storage size specifies the maximum total space available to all applications and services.

When deploying your project, the sum of all disk keys defined in and .platform/services.yaml must be equal or less than the plan storage size. For example, if your plan storage size is 5 GB, you can assign:

  • 2 GB to your application, 3 GB to your database
  • 1 GB to your application, 4 GB to your database
  • 1 GB to your application, 1 GB to your database, 3 GB to your Elasticsearch service
  • etc.

If you receive an error on git push mentioning the total disk space configured for the application and its services exceeds the plan storage size, you need to either increase the disk space reserved for your project on the project setup page or lower the storage assigned to each service and the application.

The disk key is optional. If set, it defines the size of the persistent disk of the application (in MB). Its minimum value is 256 MB and a validation error will occur if you try to set it lower.


The mounts key is an object whose keys are paths relative to the root of the application (that is, where the file lives), and values are a 2-line mount definition.

This section is optional: if your application doesn't need writable local file storage, you can omit the mounts section and set disk to the minimum value of 256.

Note that whether a mounted directory is web-accessible or not depends on the configuration of the web.locations block in Depending on the application's needs, it's possible to publish files on writable mounts, leave them private, or have rules for different paths and file types as desired.

Basic mounts

The following block defines a single writable directory, web/uploads:

        source: local
        source_path: uploads

The source specifies where the writable mount is. source_path specifies the subdirectory from within the source that the mount should point at. It is often easiest to have it match the name of the mount point itself but that is not required.

local mounts

The local source indicates that the mount point will point to a local directory on the application container. The source_path is then a subpath of that. That means they may overlap. local mounts are not shared between different application containers or workers.

Be aware that the entire local space for a single app container is a common directory, and the directory is not wiped. That means if you create a mount point with a source_path of "uploads", then write files there, then remove the mount point, the files will still exist on disk indefinitely until manually removed.

Local mounts require that the disk key be set. If it is omitted there will be no storage space available at all.

service mounts

A service mount refers to a network-storage service, as defined in services.yaml. They function in essentially the same way as a local mount, with two important differences:

1) The disk size of the service mount is controlled in services.yaml; it is separate from the value of the disk key in 2) Multiple application containers may refer to the same service mount and share files.

A service mount works like so:

    source: service
    service: files
    source_path: uploads

This assumes that a network-storage service named files has already been defined. See the Network Storage page for more details and examples.

Multi-instance disk mounts

If you have multiple application instances defined (using both web and workers), each instance will have its own local disk mounts. That's the case even if they are named the same, and even if there is only a single top-level mounts directive. In that case, every instance will have an identical configuration, but separate, independent file spaces.

If you want to have multiple application instances share file storage, you will need to use a service mount.

How do I set up both public and private file uploads?

The following example sets up two file mounts. One is mounted at /private within the application container, the other at /web/uploads. The two file mounts together have a limit of 1024 MB of storage.

disk: 1024

        source: local
        source_path: private
        source: local
        source_path: uploads

Then in the web.locations block, you'd specify that the web/uploads path is accessible. For example, this fragment would specify the /web path as the docroot but provide a more locked-down access to the /web/uploads path.

            # The public directory of the application relative to its root.
            root: 'web'
            # The front-controller script which determines where to send
            # non-static requests.
            passthru: '/app.php'
        # Allow uploaded files to be served, but do not run scripts.
            root: 'web/uploads'
            expires: 300s
            scripts: false
            allow: true

See the web locations documentation for more details.

Why can't I mount a hidden folder?

Web PaaS ignores YAML keys that start with a dot. This causes a mount like .myhiddenfolder to be ignored. If you want to mount a hidden folder, you'll have to prepend it with a /:

    source: local
    source_path: 'myhiddenfolder'

How do I setup overlapping mount paths?

While not recommended it is possible to setup multiple mount points whose source paths overlap. Consider the following example:

        source: local
        source_path: stuff
        source: local
        source_path:  stuff/secret

In this configuration, there will be two mount points as seen from the application: ~/private and ~/secret. However, the secret mount will point to a directory that is also under the mount point for private. That is, the secret path and the private/secret path will be the exact same directory.

Although this configuration won't cause any technical issues, it may be quite confusing so is generally not recommended.

Checking the size of mounts

You can use standard commands such as df -ah to find the total disk usage of mounts (which are usually all on the same filesystem) and du -hs /path/to/dir to check the size of individual directories.

The CLI provides a command that combines these checks:

$ webpaas mount:size
Checking disk usage for all mounts of the application 'app'...
| Mount(s)                | Size(s)   | Disk    | Used      | Available | Capacity |
| private                 | 55.2 MiB  | 1.9 GiB | 301.5 MiB | 1.6 GiB   | 15.5%    |
| tmp                     | 34.1 MiB  |         |           |           |          |
| web/sites/default/files | 212.2 MiB |         |           |           |          |

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