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Backup and Recovery Manager for PostgreSQL Tutorial Barman (backup and recovery manager) is an administration tool for disaster recovery of PostgreSQL servers written in Python. Barman can perform remote backups of multiple servers in business critical environments, and helps DBAs during the recovery phase. Barman's most wanted features include: backup catalogues, retention policies, remote recovery, archiving and compression of WAL files and of backups. Barman is written and maintained by PostgreSQL professionals 2ndQuadrant. __________________________________________________________________ Introduction In a perfect world, there would be no need for a backup. However it is important, especially in business environments, to be prepared for when the "unexpected" happens. In a database scenario, the unexpected could take any of the following forms: * data corruption; * system failure, including hardware failure; * human error; * natural disaster. In such cases, any ICT manager or DBA should be able to repair the incident and recover the database in the shortest possible time. We normally refer to this discipline as Disaster recovery. This guide assumes that you are familiar with theoretical disaster recovery concepts, and you have a grasp of PostgreSQL fundamentals in terms of physical backup and disaster recovery. If not, we encourage you to read the PostgreSQL documentation or any of the recommended books on PostgreSQL. Professional training on this topic is another effective way of learning these concepts. At any time of the year you can find many courses available all over the world, delivered by PostgreSQL companies such as 2ndQuadrant. For now, you should be aware that any PostgreSQL physical/binary backup (not to be confused with the logical backups produced by the pg_dump utility) is composed of: * a base backup; * one or more WAL files (usually collected through continuous archiving). PostgreSQL offers the core primitives that allow DBAs to setup a really robust Disaster Recovery environment. However, it becomes complicated to manage multiple backups, from one or more PostgreSQL servers. Restoring a given backup is another task that any PostgreSQL DBA would love to see more automated and user friendly. With these goals in mind, 2ndQuadrant started the development of Barman for PostgreSQL. Barman is an acronym for "Backup and Recovery Manager". Currently Barman works only on Linux and Unix operating systems. __________________________________________________________________ Before you start The first step is to decide the architecture of your backup. In a simple scenario, you have one PostgreSQL instance (server) running on a host. You want your data continuously backed up to another server, called the backup server. Barman allows you to launch PostgreSQL backups directly from the backup server, using SSH connections. Furthermore, it allows you to centralise your backups in case you have more than one PostgreSQL server to manage. During this guide, we will assume that: * there is one PostgreSQL instance on a host (called pg for simplicity) * there is one backup server on another host (called backup) * communication via SSH between the two servers is enabled * the PostgreSQL server can be reached from the backup server as the postgres operating system user (or another user with PostgreSQL database superuser privileges, typically configured via ident authentication) It is important to note that, for disaster recovery, these two servers must not share any physical resource except for the network. You can use Barman in geographical redundancy scenarios for better disaster recovery outcomes. System requirements * Linux/Unix * Python 2.6 or 2.7 * Python modules: + argcomplete + argh >= 0.21.2 + psycopg2 + python-dateutil < 2.0 (since version 2.0 requires python3) + distribute (optional) * PostgreSQL >= 8.4 * rsync >= 3.0.4 Important The same major version of PostgreSQL should be installed on both servers. Tip Users of RedHat Enterprise Linux, CentOS and Scientific Linux are advised to install the Extra Packages Enterprise Linux (EPEL) repository. [Further information at [1]http://fedoraproject.org/wiki/EPEL] __________________________________________________________________ Installation On RedHat/CentOS using RPM packages Barman can be installed on RHEL5 and RHEL6 Linux systems using RPM packages. Barman is available through the PostgreSQL Global Development Group RPM repository with Yum. You need to follow the instructions for your distribution (RedHat, CentOS, Fedora, etc.) and architecture that you can find at [2]http://yum.postgresql.org/. Then, as root simply type: yum install barman On Debian/Ubuntu using packages Barman can be installed on Debian and Ubuntu Linux systems using packages. It is available in the official repository for Debian Sid (unstable) and Ubuntu 12.10 (Quantal Quetzal). Note You can install an up-to-date version of Barman on many Debian and Ubuntu releases using the PostgreSQL Community APT repository at [3]http://apt.postgresql.org/. Instructions can be found at [4]https://wiki.postgresql.org/wiki/Apt. Installing Barman is as simple as typing as root user: apt-get install barman From sources Create a system user called barman on the backup server. As barman user, download the sources and uncompress them. For a system-wide installation, type: barman@backup$ ./setup.py build barman@backup# ./setup.py install # run this command with root privileges or s udo For a local installation, type: barman@backup$ ./setup.py install --user Important The --user option works only with python-distribute barman will be installed in your user directory (make sure that your PATH environment variable is set properly). __________________________________________________________________ Getting started Prerequisites SSH connection Barman needs a bidirectional SSH connection between the barman user on the backup server and the postgres user. SSH must be configured such that there is no password prompt presented when connecting. on the pg server. As the barman user on the backup server, generate an SSH key with an empty password, and append the public key to the authorized_keys file of the postgres user on the pg server. The barman user on the backup server should then be able to perform the following operation without typing a password: barman@backup$ ssh postgres@pg The procedure must be repeated with sides swapped in order to allow the postgres user on the pg server to connect to the backup server as the barman user without typing a password: postgres@pg$ ssh barman@backup For further information, refer to OpenSSH documentation. PostgreSQL connection You need to make sure that the backup server allows connection to the PostgreSQL server on pg as superuser (postgres). You can choose your favourite client authentication method among those offered by PostgreSQL. More information can be found here: [5]http://www.postgresql.org/docs/current/static/client-authentication. html barman@backup$ psql -c 'SELECT version()' -U postgres -h pg Note As of version 1.1.2, Barman honours the application_name connection option for PostgreSQL servers 9.0 or higher. Backup directory Barman needs a main backup directory to store all the backups. Even though you can define a separate folder for each server you want to back up and for each type of resource (backup or WAL segments, for instance), we suggest that you adhere to the default rules and stick with the conventions that Barman chooses for you. You will see that the configuration file (as explained below) defines a barman_home variable, which is the directory where Barman will store all your backups by default. We choose /srv/barman as home directory for Barman: barman@backup$ sudo mkdir /srv/barman barman@backup$ sudo chown barman:barman /srv/barman Important We assume that you have enough space, and that you have already thought about redundancy and safety of your disks. Basic configuration In the docs directory you will find a minimal configuration file. Use it as a template, and copy it to /etc/barman.conf, or to ~/.barman.conf. In general, the former applies to all the users on the backup server, while the latter applies only to the barman user; for the purpose of this tutorial there is no difference in using one or the other. From version 1.2.1, you can use /etc/barman/barman.conf as default system configuration file. The configuration file follows the standard INI format, and is split in: * a section for general configuration (identified by the barman label) * a section for each PostgreSQL server to be backed up (identified by the server label, e.g. main or pg) [all and barman are reserved words and cannot be used as server labels] As of version 1.1.2, you can now specify a directory for configuration files similarly to other Linux applications, using the configuration_files_directory option (empty by default). If the value of configuration_files_directory is a directory, Barman will read all the files with .conf extension that exist in that folder. For example, if you set it to /etc/barman.d, you can specify your PostgreSQL servers placing each section in a separate .conf file inside the /etc/barman.d folder. Otherwise, you can use Barman's standard way of specifying sections within the main configuration file. ; Barman, Backup and Recovery Manager for PostgreSQL ; http://www.pgbarman.org/ - http://www.2ndQuadrant.com/ ; ; Main configuration file [barman] ; Main directory barman_home = /var/lib/barman ; System user barman_user = barman ; Log location log_file = /var/log/barman/barman.log ; Default compression level: possible values are None (default), bzip2, gzip o r custom ;compression = gzip ; Pre/post backup hook scripts ;pre_backup_script = env | grep ^BARMAN ;post_backup_script = env | grep ^BARMAN ; Directory of configuration files. Place your sections in separate files with .conf extension ; For example place the 'main' server section in /etc/barman.d/main.conf ;configuration_files_directory = /etc/barman.d ; Minimum number of required backups (redundancy) ;minimum_redundancy = 0 ; Global retention policy (REDUNDANCY or RECOVERY WINDOW) - default empty ;retention_policy = ; Global bandwidth limit in KBPS - default 0 (meaning no limit) ;bandwidth_limit = 4000 ;; ; 'main' PostgreSQL Server configuration ;; [main] ;; ; Human readable description ;; description = "Main PostgreSQL Database" ;; ;; ; SSH options ;; ssh_command = ssh postgres@pg ;; ;; ; PostgreSQL connection string ;; conninfo = host=pg user=postgres ;; ;; ; Minimum number of required backups (redundancy) ;; ; minimum_redundancy = 1 ;; ;; ; Examples of retention policies ;; ;; ; Retention policy (disabled) ;; ; retention_policy = ;; ; Retention policy (based on redundancy) ;; ; retention_policy = REDUNDANCY 2 ;; ; Retention policy (based on recovery window) ;; ; retention_policy = RECOVERY WINDOW OF 4 WEEKS You can now test the configuration by executing: barman@backup$ barman show-server main barman@backup$ barman check main Write down the incoming_wals_directory, as printed by the barman show-server main command, because you will need it to setup continuous WAL archiving. Important Executing these two commands, saves you the time of manually creating backup directories for your servers. Continuous WAL archiving Edit the postgresql.conf file of the PostgreSQL instance on the pg database and activate the archive mode: wal_level = 'archive' # For PostgreSQL >= 9.0 archive_mode = on archive_command = 'rsync -a %p barman@backup:INCOMING_WALS_DIRECTORY/%f' Make sure you change the INCOMING_WALS_DIRECTORY placeholder with the value returned by the barman show-server main command above. Restart the PostgreSQL server. In order to test that continuous archiving is on and properly working, you need to check both the PostgreSQL server [For more information, refer to the PostgreSQL documentation] and the backup server (in particular, that the WAL files are collected in the destination directory). Listing the servers The following command displays the list of all the available servers: barman@backup$ barman list-server Executing a full backup To take a backup for the main server, issue the following command: barman@backup$ barman backup main As of version 1.1.0, you can serialise the backup of your managed servers by using the all target for the server: barman@backup$ barman backup all This will iterate through your available servers and sequentially take a backup for each of them. Viewing the list of backups for a server To list all the available backups for a given server, issue: barman@backup$ barman list-backup main the format of the output is as in: main - 20120529T092136 - Wed May 30 15:20:25 2012 - Size: 5.0 TiB - WAL Size: 845.0 GiB (tablespaces: tb_name:/home/tblspace/name, tb_temp:/home/tblspace/temp ) where 20120529T092136 is the ID of the backup and Wed May 30 15:20:25 2012 is the start time of the operation, Size is the size of the base backup and WAL Size is the size of WAL files archived. As of version 1.1.2, you can get a listing of the available backups for all your servers, using the all target for the server: barman@backup$ barman list-backup all Restoring a whole server To restore a whole server issue the following command: barman@backup$ barman recover main 20110920T185953 /path/to/recover/directory where 20110920T185953 is the ID of the backup to be restored. When this command completes succesfully, /path/to/recover/directory contains a complete data directory ready to be started as a PostgreSQL database server. Here is an example of a command that starts the server: barman@backup$ pg_ctl -D /path/to/recover/directory start Important If you run this command as user barman, it will become the database superuser. You can retrieve a list of backup IDs for a specific server with: barman@backup$ barman list-backup srvpgsql Remote recovery Barman is able to recover a backup on a remote server through the --remote-ssh-command COMMAND option for the recover command. If this option is specified, barman uses COMMAND to connect to a remote host. Note The postgres user is normally used to recover on a remote host. There are some limitations when using remote recovery. It is important to be aware that: * Barman needs at least 4GB of free space in the system temporary directory (usually /tmp); * the SSH connection between Barman and the remote host must use public key exchange authentication method; * PGDATA directory must exists on the remote host and the remote user must be its owner; * a directory per tablespace must exist on the remote host and the remote user must be their owner; * there must be enough free space on the remote server to contain the base backup and the WAL files needed for recovery. Restoring to a given point in time Barman employs PostgreSQL's Point-in-Time Recovery (PITR) by allowing DBAs to specify a recovery target, either as a timestamp or as a transaction ID; you can also specify whether the recovery target should be included or not in the recovery. The recovery target can be specified using one of three mutually exclusive options: * --target-time TARGET_TIME: to specify a timestamp * --target-xid TARGET_XID: to specify a transaction ID * --target-name TARGET_NAME: to specify a named restore point created previously with pg_create_restore_point(name) function call (from PostgreSQL 9.1) You can use the --exclusive option to specify whether to stop immediately before or immediately after the recovery target. Barman allows you to specify a target timeline for recovery, using the target-tli option. The notion of timeline goes beyond the scope of this document; you can find more details in the PostgreSQL documentation, or in one of 2ndQuadrant's Recovery training courses. __________________________________________________________________ WAL compression The barman cron command (see below) will compress WAL files if the compression option is set in the configuration file. This option allows three values: * gzip: for Gzip compression (requires gzip) * bzip2: for Bzip2 compression (requires bzip2) * custom: for custom compression, which requires you to set the following options as well: + custom_compression_filter: a compression filter + custom_decompression_filter: a decompression filter __________________________________________________________________ Limiting bandwidth usage From version 1.2.1 it is possible to limit the usage of I/O bandwidth through the bandwidth_limit option (global/per server), by specifying the maximum number of kilobytes per second. By default it is set to 0, meaning no limit. In case you have several tablespaces and you prefer to limit the I/O workload of your backup procedures on one or more tablespaces, you can use the tablespace_bandwidth_limit option (global/per server): tablespace_bandwidth_limit = tbname:bwlimit[, tbname:bwlimit, ...] The option accepts a comma separated list of pairs made up of the tablespace name and the bandwidth limit (in kilobytes per second). When backing up a server, Barman will try and locate any existing tablespace in the above option. If found, the specified bandwidth limit will be enforced. If not, the default bandwidth limit for that server will be applied. __________________________________________________________________ Backup ID shortcuts As of version 1.1.2, you can use any of the following shortcuts to identify a particular backup for a given server: * latest: the latest available backup for that server, in chronological order. You can also use the last synonym. * oldest: the oldest available backup for that server, in chronological order. You can also use the first synonym. These aliases can be used with any of the following commands: show-backup, delete, list-files and recover. __________________________________________________________________ Minimum redundancy safety From version 1.2.0, you can define the minimum number of periodical backups for a PostgreSQL server. You can use the global/per server configuration option called minimum_redundancy for this purpose, by default set to 0. By setting this value to any number greater than 0, Barman makes sure that at any time you will have at least that number of backups in a server catalogue. This will protect you from accidental barman delete operations. Important Make sure that your policy retention settings do not collide with minimum redundancy requirements. Regularly check Barman's log for messages on this topic. __________________________________________________________________ Retention policies From version 1.2.0, Barman supports retention policies for backups. A backup retention policy is an user-defined policy that determines how long backups and related archive logs (Write Ahead Log segments) need to be retained for recovery procedures. Based on the user's request, Barman retains the periodical backups required to satisfy the current retention policy, and any archived WAL files required for the complete recovery of those backups. Barman users can define a retention policy in terms of backup redundancy (how many periodical backups) or a recovery window (how long). Retention policy based on redundancy In a retention policy, the setting that determines how many periodical backups to keep. A redundancy-based retention policy is contrasted with retention policy that uses a recovery window. Retention policy based on recovery window A recovery window is one type of Barman backup retention policy, in which the DBA specifies a period of time and Barman ensures retention of backups and/or archived WAL files required for point-in-time recovery to any time during the recovery window. The interval always ends with the current time and extends back in time for the number of days specified by the user. For example, if the retention policy is set for a recovery window of seven days, and the current time is 9:30 AM on Friday, Barman retains the backups required to allow point-in-time recovery back to 9:30 AM on the previous Friday. Scope Retention policies can be defined for: * PostgreSQL periodical base backups: through the retention_policy configuration option; * Archive logs, for Point-In-Time-Recovery: through the wal_retention_policy configuration option. Important In a temporal dimension, archive logs must be included in the time window of periodical backups. There are two typical use cases here: full or partial point-in-time recovery. Full point in time recovery scenario Base backups and archive logs share the same retention policy, allowing DBAs to recover at any point in time from the first available backup. Partial point in time recovery scenario Base backup retention policy is wider than that of archive logs, allowing users for example to keep full weekly backups of the last 6 months, but archive logs for the last 4 weeks (granting to recover at any point in time starting from the last 4 periodical weekly backups). Important Currently, Barman implements only the full point in time recovery scenario, by constraining the wal_retention_policy option to main. How they work Retention policies in Barman can be: * automated: enforced by barman cron; * manual: Barman simply reports obsolete backups and allows DBAs to delete them. Important Currently Barman does not implement manual enforcement. This feature will be available in future versions. Configuration and syntax Retention policies can be defined through the following configuration options: * retention_policy: for base backup retention; * wal_retention_policy: for archive logs retention; * retention_policy_mode: can only be set to auto (retention policies are automatically enforced by the barman cron command). These configuration options can be defined both at a global level and a server level, allowing users maximum flexibility on a multi-server environment. Syntax for retention_policy The general syntax for a base backup retention policy through retention_policy is the following: retention_policy = {REDUNDANCY value | RECOVERY WINDOW OF value {DAYS | WEEKS | MONTHS}} Where: * syntax is case insensitive; * value is an integer and is > 0; * in case of redundancy retention policy: + value must be greater than the server minimum redundancy level (if not is is assigned to that value and a warning is generated); + the first valid backup is the value-th backup in a reverse ordered time series; * in case of recovery window policy: + the point of recoverability is: current time - window; + the first valid backup is the first available backup before the point of recoverability; its value in a reverse ordered time series must be greater than the server minimum redundancy level (if not is is assigned to that value and a warning is generated). By default, retention_policy is empty (no retention enforced). Syntax for wal_retention_policy Currently, the only allowed value for wal_retention_policy is the special value main, that maps the retention policy of archive logs to that of base backups. __________________________________________________________________ Available commands Barman commands are applied to three different levels: * general commands, which apply to the backup catalogue * server commands, which apply to a specific server (list available backups, execute a backup, etc.) * backup commands, which apply to a specific backup in the catalogue (display information, issue a recovery, delete the backup, etc.) In the following sections the available commands will be described in detail. General commands List available servers You can display the list of active servers that have been configured for your backup system with: barman list-server Maintenance mode You can perform maintenance operations, like compressing WAL files and moving them from the incoming directory to the archived one, with: barman cron This command enforces retention policies on those servers that have: * retention_policy not empty and valid; * retention_policy_mode set to auto. Note This command should be executed in a cron script. Server commands Show the configuration for a given server You can show the configuration parameters for a given server with: barman show-server <server_name> Take a base backup You can perform a full backup (base backup) for a given server with: barman backup <server_name> Tip You can use barman backup all to sequentially backup all your configured servers. Show available backups for a server You can list the catalogue of available backups for a given server with: barman list-backup <server_name> Diagnostics check You can check if the connection to a given server is properly working with: barman check <server_name> Tip You can use barman check all to check all your configured servers. Backup commands Note Remember: a backup ID can be retrieved with server list <server_name> Show backup information You can show all the available information for a particular backup of a given server with: barman show-backup <server_name> <backup_id> From version 1.1.2, in order to show the latest backup, you can issue: barman show-backup <server_name> latest Delete a backup You can delete a given backup with: barman delete <server_name> <backup_id> From version 1.1.2, in order to delete the oldest backup, you can issue: barman delete <server_name> oldest Warning Until retention policies are natively supported, you must use the oldest shortcut with extreme care and caution. Iteratively executing this command can easily wipe out your backup archive. List backup files You can list the files (base backup and required WAL files) for a given backup with: barman list-files [--target TARGET_TYPE] <server_name> <backup_id> With the --target TARGET_TYPE option, it is possible to choose the content of the list for a given backup. Possible values for TARGET_TYPE are: * data: lists just the data files; * standalone: lists the base backup files, including required WAL files; * wal: lists all WAL files from the beginning of the base backup to the start of the following one (or until the end of the log); * full: same as data + wal. The default value for TARGET_TYPE is standalone. Important The list-files command facilitates interaction with external tools, and therefore can be extremely useful to integrate Barman into your archiving procedures. __________________________________________________________________ Hook scripts As of version 1.1.0, Barman allows a database administrator to run hook scripts before and after a backup. These scripts can be configured with the following global configuration options (which can be overridden on a per server basis): * pre_backup_script: hook script launched before a base backup * post_backup_script: hook script launched after a base backup The script definition is passed to a shell and can return any exit code. The shell environment will contain the following variables: * BARMAN_BACKUP_DIR: backup destination directory * BARMAN_BACKUP_ID: ID of the backup * BARMAN_CONFIGURATION: configuration file used by barman * BARMAN_ERROR: error message, if any (only for the post phase) * BARMAN_PHASE: phase of the script, either pre or post * BARMAN_PREVIOUS_ID: ID of the previous backup (if present) * BARMAN_SERVER: name of the server * BARMAN_STATUS: status of the backup * BARMAN_VERSION: version of Barman (from 1.2.1) Important No check is performed on the exit code of the script. The result will be simply written in the log file. __________________________________________________________________ Support and sponsor opportunities Barman is free software, written and maintained by 2ndQuadrant. If you require support on using Barman, or if you need new features, please get in touch with 2ndQuadrant. You can sponsor the development of new features of Barman and PostgreSQL which will be made publicly available as open source. For further information, please visit our websites: * Barman website: [6]http://www.pgbarman.org/ * 2ndQuadrant website: [7]http://www.2ndquadrant.com/ Useful information can be found in: * the FAQ section of the website: [8]http://www.pgbarman.org/faq/ * the "Barman" category of 2ndQuadrant's blog: [9]http://blog.2ndquadrant.com/tag/barman/ __________________________________________________________________ Authors In alphabetical order: * Gabriele Bartolini <[10][email protected]> (core team) * Marco Nenciarini <[11][email protected]> (core team) Past contributors: * Carlo Ascani __________________________________________________________________ License and Contributions Barman is the exclusive property of 2ndQuadrant Italia and its code is distributed under GNU General Public License 3. Copyright © 2011-2013, 2ndQuadrant Italia (Devise.IT S.r.l.) - [12]http://www.2ndQuadrant.it. Barman has been partially funded through [13]4CaaSt, a research project funded by the European Commission's Seventh Framework programme. Contributions to Barman are welcome, and will be listed in the file AUTHORS. 2ndQuadrant Italia requires that any contributions provide a copyright assignment and a disclaimer of any work-for-hire ownership claims from the employer of the developer. This lets us make sure that all of the Barman distribution remains free code. Please contact [14][email protected] for a copy of the relevant Copyright Assignment Form. __________________________________________________________________ Last updated 2013-08-23 18:35:29 CEST References 1. http://fedoraproject.org/wiki/EPEL 2. http://yum.postgresql.org/ 3. http://apt.postgresql.org/ 4. https://wiki.postgresql.org/wiki/Apt 5. http://www.postgresql.org/docs/current/static/client-authentication.html 6. http://www.pgbarman.org/ 7. http://www.2ndquadrant.com/ 8. http://www.pgbarman.org/faq/ 9. http://blog.2ndquadrant.com/tag/barman/ 10. mailto:[email protected] 11. mailto:[email protected] 12. http://www.2ndQuadrant.it/ 13. http://4caast.morfeo-project.org/ 14. mailto:[email protected]
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