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diff --git a/doc/guide/admin/maintenance.sdf b/doc/guide/admin/maintenance.sdf new file mode 100644 index 0000000..db4b584 --- /dev/null +++ b/doc/guide/admin/maintenance.sdf @@ -0,0 +1,166 @@ +# $OpenLDAP$ +# Copyright 2007-2018 The OpenLDAP Foundation, All Rights Reserved. +# COPYING RESTRICTIONS APPLY, see COPYRIGHT. + +H1: Maintenance + +System Administration is all about maintenance, so it is only fair that we +discuss how to correctly maintain an OpenLDAP deployment. + + +H2: Directory Backups + +Backup strategies largely depend on the amount of change in the database +and how much of that change an administrator might be willing to lose in a +catastrophic failure. There are two basic methods that can be used: + +1. Backup the Berkeley database itself and periodically back up the transaction +log files: + +Berkeley DB produces transaction logs that can be used to reconstruct +changes from a given point in time. For example, if an administrator were willing to only +lose one hour's worth of changes, they could take down the server in +the middle of the night, copy the Berkeley database files offsite, and bring +the server back online. Then, on an hourly basis, they could force a +database checkpoint, capture the log files that have been generated in the +past hour, and copy them offsite. The accumulated log files, in combination +with the previous database backup, could be used with db_recover to +reconstruct the database up to the time the last collection of log files was +copied offsite. This method affords good protection, with minimal space +overhead. + + +2. Periodically run slapcat and back up the LDIF file: + +Slapcat can be run while slapd is active. However, one runs the risk of an +inconsistent database- not from the point of slapd, but from the point of +the applications using LDAP. For example, if a provisioning application +performed tasks that consisted of several LDAP operations, and the slapcat +took place concurrently with those operations, then there might be +inconsistencies in the LDAP database from the point of view of that +provisioning application and applications that depended on it. One must, +therefore, be convinced something like that won't happen. One way to do that +would be to put the database in read-only mode while performing the +slapcat. The other disadvantage of this approach is that the generated LDIF +files can be rather large and the accumulation of the day's backups could +add up to a substantial amount of space. + +You can use {{slapcat}}(8) to generate an LDIF file for each of your {{slapd}}(8) +back-bdb or back-hdb databases. + +> slapcat -f slapd.conf -b "dc=example,dc=com" + +For back-bdb and back-hdb, this command may be ran while slapd(8) is running. + +MORE on actual Berkeley DB backups later covering db_recover etc. + +H2: Berkeley DB Logs + +Berkeley DB log files grow, and the administrator has to deal with it. The +procedure is known as log file archival or log file rotation. + +Note: The actual log file rotation is handled by the Berkeley DB engine. + +Logs of current transactions need to be stored into files so that the database +can be recovered in the event of an application crash. Administrators can change +the size limit of a single log file (by default 10MB), and have old log files +removed automatically, by setting up DB environment (see below). The reason +Berkeley DB never deletes any log files by default is that the administrator +may wish to backup the log files before removal to make database recovery +possible even after a catastrophic failure, such as file system corruption. + +Log file names are {{F:log.XXXXXXXXXX}} (X is a digit). By default the log files +are located in the BDB backend directory. The {{F:db_archive}} tool knows what +log files are used in current transactions, and what are not. Administrators can +move unused log files to a backup media, and delete them. To have them removed +automatically, place set_flags {{DB_LOG_AUTOREMOVE}} directive in {{F:DB_CONFIG}}. + +Note: If the log files are removed automatically, recovery after a catastrophic +failure is likely to be impossible. + +The files with names {{F:__db.001}}, {{F:__db.002}}, etc are just shared memory +regions (or whatever). These ARE NOT 'logs', they must be left alone. Don't be +afraid of them, they do not grow like logs do. + +To understand the {{F:db_archive}} interface, the reader should refer to +chapter 9 of the Berkeley DB guide. In particular, the following chapters are +recommended: + +* Database and log file archival - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/archival.html}} +* Log file removal - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/logfile.html}} +* Recovery procedures - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/recovery.html}} +* Hot failover - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/hotfail.html}} +* Complete list of Berkeley DB flags - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/api_c/env_set_flags.html}} + +Advanced installations can use special environment settings to fine-tune some +Berkeley DB options (change the log file limit, etc). This can be done by using +the {{F:DB_CONFIG}} file. This magic file can be created in BDB backend directory +set up by {{slapd.conf}}(5). More information on this file can be found in File +naming chapter. Specific directives can be found in C Interface, look for +{{DB_ENV->set_XXXX}} calls. + +Note: options set in {{F:DB_CONFIG}} file override options set by OpenLDAP. +Use them with extreme caution. Do not use them unless You know what You are doing. + +The advantages of {{F:DB_CONFIG}} usage can be the following: + +* to keep data files and log files on different mediums (i.e. disks) to improve + performance and/or reliability; +* to fine-tune some specific options (such as shared memory region sizes); +* to set the log file limit (please read Log file limits before doing this). + +To figure out the best-practice BDB backup scenario, the reader is highly +recommended to read the whole Chapter 9: Berkeley DB Transactional Data Store Applications. +This chapter is a set of small pages with examples in C language. Non-programming +people can skip these examples without loss of knowledge. + + +H2: Checkpointing + +MORE/TIDY + +If you put "checkpoint 1024 5" in slapd.conf (to checkpoint after 1024kb or 5 minutes, +for example), this does not checkpoint every 5 minutes as you may think. +The explanation from Howard is: + +'In OpenLDAP 2.1 and 2.2 the checkpoint directive acts as follows - *when there +is a write operation*, and more than <check> minutes have occurred since the +last checkpoint, perform the checkpoint. If more than <check> minutes pass after +a write without any other write operations occurring, no checkpoint is performed, +so it's possible to lose the last write that occurred.'' + +In other words, a write operation occurring less than "check" minutes after the +last checkpoint will not be checkpointed until the next write occurs after "check" +minutes have passed since the checkpoint. + +This has been modified in 2.3 to indeed checkpoint every so often; in the meantime +a workaround is to invoke "db_checkpoint" from a cron script every so often, say 5 minutes. + +H2: Migration + +The simplest steps needed to migrate between versions or upgrade, depending on your deployment +type are: + +.{{S: }} +^{{B: Stop the current server when convenient}} + +.{{S: }} ++{{B: slapcat the current data out}} + +.{{S: }} ++{{B: Clear out the current data directory (/usr/local/var/openldap-data/) leaving DB_CONFIG in place}} + +.{{S: }} ++{{B: Perform the software upgrades}} + +.{{S: }} ++{{B: slapadd the exported data back into the directory}} + +.{{S: }} ++{{B: Start the server}} + +Obviously this doesn't cater for any complicated deployments like {{SECT: MirrorMode}} or {{SECT: N-Way Multi-Master}}, +but following the above sections and using either commercial support or community support should help. Also check the +{{SECT: Troubleshooting}} section. + + |