UBOS Backup format

/docs/developers/details/backup-format/

The Idea

The UBOS Backup File Format defines how to store, in a single file, all data and meta-data necessary to reconstruct the installation of one or more Apps at one or more Sites. This supports use cases such as backup, restore, archival, checkpointing, QA and many others.

This file format can be defined once in an application-independent manner, and thus can be used by all Apps.

Philosophy

We use ZIP. We chose it over tar because ZIP has better random-access capabilities; tar is intended to be read sequentially.

We store full meta-data for the Sites and AppConfigurations whose data is stored in the backup. This allows users to restore Sites and/or AppConfigurations without having to provide additional information.

Note that the individual items in the ZIP file generally do not directly map to files and directories on a file system as explained below.

Files in this format generally use extension .ubos-backup. Any of the entries in the ZIP file may be deflated (aka compressed) according to standard ZIP conventions.

When an encrypted backup is desired, the entire .ubos-backup file is encrypted with GPG, and be convention, the file extension becomes .ubos-backup.gpg.

Meta-data

filetype
This file contains a fixed string to identify this ZIP file as a UBOS backup file in version 1.

Fixed string: UBOS::Backup::ZipFileBackup;v1

starttime
This file contains the (starting) time at which this backup file was being created, in the UTC time zone in RFC 3339 format.

Example: 2014-12-31T23:59:01.234Z

sites/
This directory contains the Site JSON files of all Sites that have been backed up to this file.

For example:

sites/s1111111111222222222233333333334444444444.json
The Site JSON file for a Site with SiteId s111111111122222222223333333333334444444444, which has been backed up to this backup file. The name of the file must be the SiteId of the Site, plus the .json postfix. This file is only present for those Sites that have been backed up as a whole to this backup file.

If additional Sites have been backed up to this file, their Site JSON files would also be found in this directory.

installables/
This directory contains the UBOS Manifest JSON files of all Apps and Accessories of all the Sites in the backup, in the version they were running at the time the backup was created. This helps to reconcile version differences at the time of restore.
installables/gladiwashere-php-mysql.json
The UBOS Manifest file of the gladiwashere-php-mysql example App. The name of this file must be the App’s or Accessory’s Package name, plus the .json postfix.

In-ZIP hierarchical structure

All other content of the ZIP file is structured:

This structure is similar to the structure of JSON files and UBOS Manifest files. This allows a backup file to contain the data of several installations of the same application without conflicts (for example, two Wordpress installations at different virtual hosts or relative path name).

The file may contain AppConfigurations that are not part of a Site; i.e. there is no Site JSON in the sites/ directory discussed above that mentions them. This occurs when only an AppConfiguration instead of an entire Site was backed up to this backup file.

The appconfigs/ directory is structured as follows:

appconfigs/
Parent directory of all the backed-up data.
appconfigs/a4444444444333333333322222222221111111111.json
The fragment of the Site JSON file that belongs to this AppConfiguration. This fragment is present here regardless of whether the full Site JSON file is present in the sites/ directory discussed above.
appconfigs/a4444444444333333333322222222221111111111/
This directory contains data which was backed up from the AppConfiguration whose AppConfigId has value a4444444444333333333322222222221111111111. To determine which Site this AppConfiguration belonged to at the time of backup, consult the Site JSON files above. However, it may be that only the AppConfiguration was backed up, not the entire Site, so there may not be a Site JSON file that refers to this AppConfiguration.
appconfigs/a4444444444333333333322222222221111111111/gladiwashere-php-mysql/
This directory contains data which was backed up from the gladiwashere-php-mysql example App at this AppConfiguration. The name of this directory is the Package name of the App or Accessory whose data is backed up in this directory.
appconfigs/a4444444444333333333322222222221111111111/gladiwashere-php-mysql/apache2/
This directory contains data which was backed up from Role apache2 of this App or Accessory at this AppConfiguration. Any Role may have a section here.
appconfigs/a4444444444333333333322222222221111111111/gladiwashere-php-mysql/apache2/uploads
The name of the Retention Bucket that was backed up. This is the same as specified in the UBOS Manifest file by the App or Accessory. The toy app gladiwashere-php-mysql doesn’t actually define an uploads Retention Bucket, but if it did, the relevant part of the UBOS Manifest would look like this:
{
    ...
    "retention"       : "backup",
    "retentionbucket" : "uploads"
}

Depending on the type of item that is being backed up, this may be a file or a directory.

Content storage

This section documents how content of various types is represented in a backup file. Additional types of content may be defined in the future.

File and directory content

Assume that a directory /ubos/http/sites/s1111111111222222222233333333334444444444/blog/uploads of some web App needs to be backed up. Let’s assume that this directory belongs to an App that has been installed at Context Path /blog of some Site (App Package myapp, SiteId s1111111111222222222233333333334444444444, AppConfigId a4444444444333333333322222222221111111111).

Let’s also assume this App has declared in its UBOS Manifest the directory AppConfigItem for the apache2 Role like this :

{
    "type"            : "directory",
    "name"            : "uploads",
    "retention"       : "backup",
    "retentionbucket" : "uploadsdir"
    ...
}

Then, the recursive directory tree starting with root directory /ubos/http/sites/s1111111111222222222233333333334444444444/blog/uploads will be backed up to appconfigs/a4444444444333333333322222222221111111111/myapp/apache2/uploadsdir in the backup file.

Note that the filename in the ZIP file comes from the retentionbucket field in the UBOS Manifest, and not from the name field or the name of the App or Accessory. That way, the names of files and directories can be easily changed from one version of the App or Accessory to the next without impacting future or old backups.

MySQL database content

Assume that the UBOS Manifest of some App or Accessory declares a database as one of its AppConfigItems in the mysql Role (App or Accessory Package myapp, SiteId s1111111111222222222233333333334444444444, AppConfigId a4444444444333333333322222222221111111111).

Let’s also assume this App has declared in its UBOS Manifest that it wishes the database to be backed up, like this:

{
    "type"            : "database",
    "name"            : "maindb",
    "retention"       : "backup",
    "retentionbucket" : "maindb.mysqldump",
    ...
}

Then, upon backup, the content of the MySQL database will be exported by UBOS with the mysqldump tool to a file called maindb.mysqldump in directory appconfigs/a4444444444333333333322222222221111111111/myapp/mysql/ in the backup file.

Note that the filename in the backup file comes from the retentionbucket field in the UBOS Manifest, not from the name field or the name of the App nor from the actual MySQL database name in the running App.

Postgresql database content

Assume that the UBOS Manifest of some App or Accessory declares a database as one of its AppConfigItems in the postgresql Role (App or Accessory Package myapp, SiteId s1111111111222222222233333333334444444444, AppConfigId a4444444444333333333322222222221111111111).

Let’s also assume this App has declared in its UBOS Manifest that it wishes the database to be backed up, like this:

{
    "type"            : "database",
    "name"            : "maindb",
    "retention"       : "backup",
    "retentionbucket" : "maindb.dump",
    ...
}

Then, upon backup, the content of the Postgresql database will be exported by UBOS with the pg_dump tool to a file called maindb.dump in directory appconfigs/a4444444444333333333322222222221111111111/myapp/postgresql/ in the backup file.

Note that the filename in the backup file comes from the retentionbucket field in the UBOS Manifest, not from the name field or the name of the App nor from the actual Postgresql database name in the running App.