Plesk provides the option of choosing a remote storage to keep your
backups, such as an FTP server. Using Plesk SDK, it is also possible to
add more different custom backup storages, and enable Plesk to use them
to keep the backups.

Class
pm_Hook_Backup_Transport
defines a set of methods, which describe the necessary functions of
authentication and authorization, working with files, etc. With the help
of this hook, Plesk Backup Manager knows about the new custom storage,
and provides all the same operations and information that are available
for the default backup storages.

To illustrate the subject, the following sample project is provided by
Plesk: https://github.com/plesk/ext-cloud-backup-example.

Authorization

As the extension developer, you may choose to handle authorization,
using either OAuth2 or login and password.

Login and Password

The login and password (or access key/secret key) used for
authentication with the custom storage are specified on the custom
storage settings sub-form,
pm_Hook_Backup_Transport::getSettingsSubForm(),
along with other settings. The entered login and password must be
validated in the
pm_Form_SubForm::isValid()
method.

OAuth2

OAuth2 authorization must be implemented in the
pm_Hook_Backup_Transport::authorize()
method. This method is always called before displaying the custom
storage settings sub-form,
pm_Hook_Backup_Transport::getSettingsSubForm().

Verification

Method
pm_Hook_Backup_Transport::check()
should be used to make sure all the functions involved in backup and
restore operations (e.g., CRUD) are available. This method is called
before each backup operation.

Remarks

1. Make sure to use the Plesk Key-Value Storage to
   encrypt and safely store passwords and access tokens.
2. Create separate directories in the custom storage root directory for
   the different objects to keep their backup files from mixing.

Working with Files

Writing to Custom Storage

The methods responsible for writing the created backup to the custom
storage are called in the following order:

1. openFileWrite()
2. [multiple calls]
   appendFile()
3. closeFile()

Some storages may require the size of the file written to be known
before starting the file upload. This information is not available
during the Plesk backup creation. In this case, the backup should be
split into a set of files of a known size. The files should be named in
the following manner:

1. backup.tar
2. backup.tar1
3. backup.tar2
4. ...

This way, Plesk Backup Manager will be able to correctly display
information and work with the backup.

Reading from Custom Storage

The methods responsible for reading the backup from the custom storage
are called in the following order:

1. openFileRead()
2. [multiple calls]
   readFile()
3. closeFile()

Testing Your Extension with Custom Storage

To make sure all the backup/restore-related extension functions work
properly, run the following command:

/opt/psa/admin/bin/pmm-ras --check-repository --debug --verbose --dump-storage=ext://<ext name>/subscription/<id>/ --session-path=/var/log/plesk/PMM