[WIP] allow configuring multiple object store backends

[icewind1991]

🚧

Allow configuring multiple object store backends to allow further load balancing and easier migration.

By default everything is put in the "default" bucket, objects for the root storage are put in the "root" bucket if it exists ("default" if it doesn't), the backend for users can be set with a user preference option (occ user:setting <user> homeobjectstore objectstore <config key>).

Existing objectstore and objectstore_multibucket configurations are handled transparently.

Migration example

Migrating users to a new s3 server could be done with the following steps:

• copy the "default" configuration to a new "old" configuration
• set the objectstore config key for all existing users to "old"
• change the "default" configuration to the new s3 server

all new users will now be stored on the new s3 server, existing users can now be migrated one-by-one with minimal downtime

• copy over the objects for a single user to the new s3 server
• update the objectstore config key for the user

example configuration:

[
  'objectstore' => [
    'default' => [
      'class' => 'OC\\Files\\ObjectStore\\S3',
      'arguments' => [
        'multibucket' => true,
        'bucket' => 'nextcloud-',
        'hostname' => 'objectstore2',
        ...
      ],
    ],
    'old' => [
      'class' => 'OC\\Files\\ObjectStore\\S3',
      'arguments' => [
        'bucket' => 'nextcloud',
        'hostname' => 'objectstore1',
        ...
      ],
    ],
    'root' => [
      'class' => 'OC\\Files\\ObjectStore\\S3',
      'arguments' => [
        'bucket' => 'nextcloud-root',
        'hostname' => 'objectstore1',
        ...
      ],
    ],
  ],
]

For a use case where all objects in the root storage is put in "objectstore1/nextcloud-root", users created before the objectstore migration have the "homeobjectstore.objectstore" config option set to "old" and have their objects stored in "objectstore1/nextcloud" which all users created afterwards have their objects stored in the "objectstore2/nextcloud-XX" buckets.

todo

• command to move users from "default" to ""
  • create "" objectstore configuration as a copy from "default"
  • for all users who are currently using "default" set the objectstore config key to ""
  • if the root storage is using "default", copy the "default" configuration to "root"
• command to migrate users to a different config
  • same as multibucket_migrate but for objectstore configs instead of buckets
• command to list users by configuration