Documentation/backup.txt - gerrit - Git at Google

 :linkattrs:
 = Gerrit Code Review - Backup

 A Gerrit Code Review site contains data that needs to be backed up regularly.
 This document describes best practices for backing up review data.

 [#mand-backup]
 == Data which must be backed up

 [#mand-backup-git]
 Git repositories::
 +
 The bare Git repositories managed by Gerrit are typically stored in the
 `${SITE}/git` directory. However, the locations can be customized in
 `${site}/etc/gerrit.config`. They contain the history of the respective
 projects, and since 2.15 if you are using _NoteDb_, and for 3.0 and newer,
 also change and review metadata, user accounts and groups.
 +

 [#mand-backup-db]
 SQL database::
 +
 Gerrit releases in the 2.x series store some data in the database you
 have chosen when installing Gerrit. If you are using 2.16 and have
 migrated to _NoteDb_ only the schema version is stored in the database.
 +
 If you are using h2 you need to backup the `.db` files in the folder
 `${SITE}/db`.
 +
 For all other database types refer to their backup documentation.
 +
 Gerrit release 3.0 and newer store all primary data in _NoteDb_ inside
 the git repositories of the Gerrit site. Only the review flag marking in
 the UI when you have reviewed a changed file is stored in a relational
 database. If you are using h2 this database is named
 `account_patch_reviews.h2.db`.

 [#optional-backup]
 == Data optional to be backed up

 [#data-optional-backup-index]
 Search index::
 +
 The _Lucene_ search index is stored in the `${SITE}/index` folder.
 It can be recomputed from primary data in the git repositories but
 reindexing may take a long time hence backing up the index makes sense
 for production installations.

 [#optional-backup-cache]
 Caches::
 +
 Gerrit uses many caches which populate automatically. Some of the caches
 are persisted in the directory `${SITE}/cache` to retain the cached data
 across restarts. Since repopulating persistent caches takes time and server
 resources it makes sense to include them in backups to avoid unnecessary
 higher load and degraded performance when a Gerrit site has been restored
 from backup and caches need to be repopulated.

 [#optional-backup-config]
 Configuration::
 +
 Gerrit configuration files are located in the directory `${SITE}/etc`
 and should be backed up or versioned in a git repository. The `etc`
 directory also contains secrets which should be handled separately
 +
 * `secure.config` contains passwords and `auth.registerEmailPrivateKey`
 * public and private SSH host keys
 +
 You may consider to use the
 link:https://gerrit.googlesource.com/plugins/secure-config/[secure-config plugin,role=external,window=_blank]
 to encrypt these secrets.

 [#optional-backup-plugin-data]
 Plugin Data::
 +
 The `${SITE}/data/` directory is used by plugins storing data like e.g.
 the delete-project and the replication plugin.

 [#optional-backup-libs]
 Libraries::
 +
 The `${SITE}/lib/` directory contains libraries used as statically loaded
 plugin or providing additional dependencies needed by Gerrit plugins.

 [#optional-backup-plugins]
 Plugins::
 +
 The `${SITE}/plugins/` directory contains the installed Gerrit plugins.

 [#optional-backup-static]
 Static Resources::
 +
 The `${SITE}/static/` directory contains static resources used to customize the
 Gerrit UI and email templates.

 [#optional-backup-logs]
 Logs::
 +
 The `${SITE}/logs/` directory contains Gerrit server log files. Logs can still
 be written when the server is in read-only mode.

 [#cons-backup]
 == Consistent backups

 There are several ways to ensure consistency when backing up primary data.

 [#cons-backup-snapshot]
 === Filesystem snapshots

 Gerrit 3.0 or newer::
 +
 * all primary data is stored in git
 * Use a file system like lvm, zfs, btrfs or nfs supporting snapshots.
 Create a snapshot and then archive the snapshot.

 Gerrit 2.x::
 +
 Gerrit 2.16 can use _NoteDb_ to store almost all this data which
 simplifies creating backups since consistency between database and git
 repositories is no longer critical. If you migrated to _NoteDb_ you can
 follow the backup procedure for 3.0 and higher and additionally take
 a backup of the database, which only contains the schema version,
 hence consistency between git and database is no longer critical since
 the schema version only changes during upgrade. If you didn't migrate
 to _NoteDb_ then follow the backup procedure for older 2.x Gerrit versions.
 +
 Older 2.x Gerrit versions store change meta data, review comments, votes,
 accounts and group information in a SQL database. Creating consistent backups
 where git repositories and the data stored in the database are backed up
 consistently requires to turn the server read-only or to shut it down
 while creating the backup since there is no integrated transaction handling
 between git repositories and the SQL database. Also crons and currently
 running cron jobs (e.g. repacking repositories) which affect the repositories
 may need to be shut down.
 Use a file system supporting snapshots to keep the period where the gerrit
 server is read-only or down as short as possible.

 [#cons-backup-read-only]
 === Turn primary server read-only for backup

 Make the primary server handling write operations read-only before taking the
 backup. This means read-access is still available from replica servers during
 backup, because only write operations have to be stopped to ensure consistency.
 This can be implemented using the
 link:https://gerrit.googlesource.com/plugins/readonly/[_readonly_,role=external,window=_blank] plugin.

 [#cons-backup-replicate]
 === Replicate data for backup

 Replicating the git repositories can backup the most critical repository data
 but does not backup repository meta-data such as the project description
 file, ref-logs, git configs, and alternate configs.

 Replicate all git repositories to another file system using
 `git clone --mirror`,
 or the
 link:https://gerrit.googlesource.com/plugins/replication[replication plugin,role=external,window=_blank]
 or the
 link:https://gerrit.googlesource.com/plugins/pull-replication[pull-replication plugin,role=external,window=_blank].
 Best you use a filesystem supporting snapshots to create a backup archive
 of such a replica.

 For 2.x Gerrit versions also set up a database replica for the data stored in the
 SQL database. If you are using 2.16 and migrated to _NoteDb_ you may consider to
 skip setting up a database replica, instead take a backup of the database which only
 contains the current schema version in this case.
 In addition you need to ensure that no write operations are in flight before you
 take the replica offline. Otherwise the database backup might be inconsistent
 with the backup of the git repositories.

 Do not skip backing up the replica, the replica alone IS NOT a backup.
 Imagine someone deleted a project by mistake and this deletion got replicated.
 Replication of repository deletions can be switched off using the
 link:https://gerrit.googlesource.com/plugins/replication/+/refs/heads/master/src/main/resources/Documentation/config.md[server option,role=external,window=_blank]
 `remote.NAME.replicateProjectDeletions`.

 If you are using Gerrit replica to offload read traffic you can use one of these
 replica for creating backups.

 [#cons-backup-offline]
 === Take primary server offline for backup

 Shut down the primary server handling write operations before taking a backup.
 This is simple but means downtime for the users. Also crons and currently
 running cron jobs (e.g. repacking repositories) which affect the repositories
 may need to be shut down.

 [#backup-methods]
 == Backup methods

 [#backup-methods-snapshots]
 === Filesystem snapshots

 Filesystems supporting copy on write snapshots::
 +
 Use a file system supporting copy-on-write snapshots like
 link:https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Snapshots[btrfs,role=external,window=_blank]
 or
 https://wiki.debian.org/ZFS#Snapshots[zfs,role=external,window=_blank].


 Other filesystems supporting snapshots::
 https://wiki.archlinux.org/index.php/LVM#Snapshots[lvm,role=external,window=_blank] or nfs.
 +
 Create a snapshot and then archive the snapshot to another storage.
 +
 While snapshots are great for creating high quality backups quickly, they are
 not ideal as a format for storing backup data. Snapshots typically depend and
 reside on the same storage infrastructure as the original disk images.
 Therefore, it’s crucial that you archive these snapshots and store them
 elsewhere.

 3.0 or newer::
 Snapshot the complete site directory

 2.x::
 Similar, but the data of the database should be stored on the very same volume
 on the same machine, so that the snapshot is taken atomically over both
 the git data and the database data. Because everything should be ACID, it can safely
 crash-recover - as if the power has been plugged and the server got booted up again.
 (Actually more safe than that, because the filesystem knows about taking the snapshot,
 and also about the pending writes it can sync.)

 In addition to that, using filesystem snapshots allows to:

 * easy and fast roll back without having to access remote backup data (e.g. to restore
 accidental rm -rf git/ back in seconds).
 * incremental transfer of consistent snapshots
 * save a lot of data while still keeping multiple "known consistent states"

 [#backup-methods-other]
 === Other backup methods

 To ensure consistent backups these backup methods require to turn the server into
 read-only mode while a backup is running.

 * create an archive like `tar.gz` to backup the site
 * `rsync`
 * plain old `cp`

 [#backup-methods-test]
 == Test backups

 Test backups and fire drill restoring backups to ensure the backups aren't
 corrupt or incomplete and you can restore a backup quickly.

 [#backup-dr]
 == Disaster recovery

 [#backup-dr-repl]
 === Replicate backup archives

 To enable disaster recovery at least replicate backup archives to another data center.
 And fire drill restoring a new site using the backup.

 [#backup-dr-multi-site]
 === Multi-site setup

 Use the https://gerrit.googlesource.com/plugins/multi-site[multi-site plugin,role=external,window=_blank]
 to install Gerrit with multiple sites installed in different datacenters
 across different regions. This ensures that in case of a severe problem with
 one of the sites, the other sites can still serve your repositories.

 GERRIT
 ------
 Part of link:index.html[Gerrit Code Review]

 SEARCHBOX
 ---------
	:linkattrs:
	= Gerrit Code Review - Backup

	A Gerrit Code Review site contains data that needs to be backed up regularly.
	This document describes best practices for backing up review data.

	[#mand-backup]
	== Data which must be backed up

	[#mand-backup-git]
	Git repositories::
	+
	The bare Git repositories managed by Gerrit are typically stored in the
	`${SITE}/git` directory. However, the locations can be customized in
	`${site}/etc/gerrit.config`. They contain the history of the respective
	projects, and since 2.15 if you are using _NoteDb_, and for 3.0 and newer,
	also change and review metadata, user accounts and groups.
	+

	[#mand-backup-db]
	SQL database::
	+
	Gerrit releases in the 2.x series store some data in the database you
	have chosen when installing Gerrit. If you are using 2.16 and have
	migrated to _NoteDb_ only the schema version is stored in the database.
	+
	If you are using h2 you need to backup the `.db` files in the folder
	`${SITE}/db`.
	+
	For all other database types refer to their backup documentation.
	+
	Gerrit release 3.0 and newer store all primary data in _NoteDb_ inside
	the git repositories of the Gerrit site. Only the review flag marking in
	the UI when you have reviewed a changed file is stored in a relational
	database. If you are using h2 this database is named
	`account_patch_reviews.h2.db`.

	[#optional-backup]
	== Data optional to be backed up

	[#data-optional-backup-index]
	Search index::
	+
	The _Lucene_ search index is stored in the `${SITE}/index` folder.
	It can be recomputed from primary data in the git repositories but
	reindexing may take a long time hence backing up the index makes sense
	for production installations.

	[#optional-backup-cache]
	Caches::
	+
	Gerrit uses many caches which populate automatically. Some of the caches
	are persisted in the directory `${SITE}/cache` to retain the cached data
	across restarts. Since repopulating persistent caches takes time and server
	resources it makes sense to include them in backups to avoid unnecessary
	higher load and degraded performance when a Gerrit site has been restored
	from backup and caches need to be repopulated.

	[#optional-backup-config]
	Configuration::
	+
	Gerrit configuration files are located in the directory `${SITE}/etc`
	and should be backed up or versioned in a git repository. The `etc`
	directory also contains secrets which should be handled separately
	+
	* `secure.config` contains passwords and `auth.registerEmailPrivateKey`
	* public and private SSH host keys
	+
	You may consider to use the
	link:https://gerrit.googlesource.com/plugins/secure-config/[secure-config plugin,role=external,window=_blank]
	to encrypt these secrets.

	[#optional-backup-plugin-data]
	Plugin Data::
	+
	The `${SITE}/data/` directory is used by plugins storing data like e.g.
	the delete-project and the replication plugin.

	[#optional-backup-libs]
	Libraries::
	+
	The `${SITE}/lib/` directory contains libraries used as statically loaded
	plugin or providing additional dependencies needed by Gerrit plugins.

	[#optional-backup-plugins]
	Plugins::
	+
	The `${SITE}/plugins/` directory contains the installed Gerrit plugins.

	[#optional-backup-static]
	Static Resources::
	+
	The `${SITE}/static/` directory contains static resources used to customize the
	Gerrit UI and email templates.

	[#optional-backup-logs]
	Logs::
	+
	The `${SITE}/logs/` directory contains Gerrit server log files. Logs can still
	be written when the server is in read-only mode.

	[#cons-backup]
	== Consistent backups

	There are several ways to ensure consistency when backing up primary data.

	[#cons-backup-snapshot]
	=== Filesystem snapshots

	Gerrit 3.0 or newer::
	+
	* all primary data is stored in git
	* Use a file system like lvm, zfs, btrfs or nfs supporting snapshots.
	Create a snapshot and then archive the snapshot.

	Gerrit 2.x::
	+
	Gerrit 2.16 can use _NoteDb_ to store almost all this data which
	simplifies creating backups since consistency between database and git
	repositories is no longer critical. If you migrated to _NoteDb_ you can
	follow the backup procedure for 3.0 and higher and additionally take
	a backup of the database, which only contains the schema version,
	hence consistency between git and database is no longer critical since
	the schema version only changes during upgrade. If you didn't migrate
	to _NoteDb_ then follow the backup procedure for older 2.x Gerrit versions.
	+
	Older 2.x Gerrit versions store change meta data, review comments, votes,
	accounts and group information in a SQL database. Creating consistent backups
	where git repositories and the data stored in the database are backed up
	consistently requires to turn the server read-only or to shut it down
	while creating the backup since there is no integrated transaction handling
	between git repositories and the SQL database. Also crons and currently
	running cron jobs (e.g. repacking repositories) which affect the repositories
	may need to be shut down.
	Use a file system supporting snapshots to keep the period where the gerrit
	server is read-only or down as short as possible.

	[#cons-backup-read-only]
	=== Turn primary server read-only for backup

	Make the primary server handling write operations read-only before taking the
	backup. This means read-access is still available from replica servers during
	backup, because only write operations have to be stopped to ensure consistency.
	This can be implemented using the
	link:https://gerrit.googlesource.com/plugins/readonly/[_readonly_,role=external,window=_blank] plugin.

	[#cons-backup-replicate]
	=== Replicate data for backup

	Replicating the git repositories can backup the most critical repository data
	but does not backup repository meta-data such as the project description
	file, ref-logs, git configs, and alternate configs.

	Replicate all git repositories to another file system using
	`git clone --mirror`,
	or the
	link:https://gerrit.googlesource.com/plugins/replication[replication plugin,role=external,window=_blank]
	or the
	link:https://gerrit.googlesource.com/plugins/pull-replication[pull-replication plugin,role=external,window=_blank].
	Best you use a filesystem supporting snapshots to create a backup archive
	of such a replica.

	For 2.x Gerrit versions also set up a database replica for the data stored in the
	SQL database. If you are using 2.16 and migrated to _NoteDb_ you may consider to
	skip setting up a database replica, instead take a backup of the database which only
	contains the current schema version in this case.
	In addition you need to ensure that no write operations are in flight before you
	take the replica offline. Otherwise the database backup might be inconsistent
	with the backup of the git repositories.

	Do not skip backing up the replica, the replica alone IS NOT a backup.
	Imagine someone deleted a project by mistake and this deletion got replicated.
	Replication of repository deletions can be switched off using the
	link:https://gerrit.googlesource.com/plugins/replication/+/refs/heads/master/src/main/resources/Documentation/config.md[server option,role=external,window=_blank]
	`remote.NAME.replicateProjectDeletions`.

	If you are using Gerrit replica to offload read traffic you can use one of these
	replica for creating backups.

	[#cons-backup-offline]
	=== Take primary server offline for backup

	Shut down the primary server handling write operations before taking a backup.
	This is simple but means downtime for the users. Also crons and currently
	running cron jobs (e.g. repacking repositories) which affect the repositories
	may need to be shut down.

	[#backup-methods]
	== Backup methods

	[#backup-methods-snapshots]
	=== Filesystem snapshots

	Filesystems supporting copy on write snapshots::
	+
	Use a file system supporting copy-on-write snapshots like
	link:https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Snapshots[btrfs,role=external,window=_blank]
	or
	https://wiki.debian.org/ZFS#Snapshots[zfs,role=external,window=_blank].


	Other filesystems supporting snapshots::
	https://wiki.archlinux.org/index.php/LVM#Snapshots[lvm,role=external,window=_blank] or nfs.
	+
	Create a snapshot and then archive the snapshot to another storage.
	+
	While snapshots are great for creating high quality backups quickly, they are
	not ideal as a format for storing backup data. Snapshots typically depend and
	reside on the same storage infrastructure as the original disk images.
	Therefore, it’s crucial that you archive these snapshots and store them
	elsewhere.

	3.0 or newer::
	Snapshot the complete site directory

	2.x::
	Similar, but the data of the database should be stored on the very same volume
	on the same machine, so that the snapshot is taken atomically over both
	the git data and the database data. Because everything should be ACID, it can safely
	crash-recover - as if the power has been plugged and the server got booted up again.
	(Actually more safe than that, because the filesystem knows about taking the snapshot,
	and also about the pending writes it can sync.)

	In addition to that, using filesystem snapshots allows to:

	* easy and fast roll back without having to access remote backup data (e.g. to restore
	accidental rm -rf git/ back in seconds).
	* incremental transfer of consistent snapshots
	* save a lot of data while still keeping multiple "known consistent states"

	[#backup-methods-other]
	=== Other backup methods

	To ensure consistent backups these backup methods require to turn the server into
	read-only mode while a backup is running.

	* create an archive like `tar.gz` to backup the site
	* `rsync`
	* plain old `cp`

	[#backup-methods-test]
	== Test backups

	Test backups and fire drill restoring backups to ensure the backups aren't
	corrupt or incomplete and you can restore a backup quickly.

	[#backup-dr]
	== Disaster recovery

	[#backup-dr-repl]
	=== Replicate backup archives

	To enable disaster recovery at least replicate backup archives to another data center.
	And fire drill restoring a new site using the backup.

	[#backup-dr-multi-site]
	=== Multi-site setup

	Use the https://gerrit.googlesource.com/plugins/multi-site[multi-site plugin,role=external,window=_blank]
	to install Gerrit with multiple sites installed in different datacenters
	across different regions. This ensures that in case of a severe problem with
	one of the sites, the other sites can still serve your repositories.

	GERRIT
	------
	Part of link:index.html[Gerrit Code Review]

	SEARCHBOX
	---------