H3: MirrorMode
MirrorMode is a hybrid configuration that provides all of the consistency
-guarantees of single-master replication while also providing the high
+guarantees of single-master replication, while also providing the high
availability of multi-master. In MirrorMode two masters are set up to
replicate from each other (as a multi-master configuration) but an
external frontend is employed to direct all writes to only one of
repaired and restarted it will automatically catch up to any changes
on the running master and resync.
+This is discussed in full in the {{SECT:MirrorMode}} section below
+
H2: LDAP Sync Replication
The {{TERM:LDAP Sync}} Replication engine, {{TERM:syncrepl}} for
H2: MirrorMode
+H3: Arguments for MirrorMode
+
+* Provides a high-availability (HA) solution for directory writes (replicas handle reads)
+* As long as one Master is operational, writes can safely be excepted
+* Master nodes replicate from each other, so they are always up to date and
+can be ready to take over (hot standby)
+* Syncrepl also allows the master nodes to re-synchronize after any downtime
+* Delta-Syncrepl can be used
+
+
+H3: Arguments against MirrorMode
+
+* MirrorMode is not what is termed as a Multi-Master solution. This is because
+writes have to go to one of the mirror nodes at a time
+* MirrorMode can be termed as Active-Active Hot-Standby, therefor an external
+server (slapd in proxy mode) or device (hardware load balancer) to manage which
+master is currently active
+* While syncrepl can recover from a completely empty database, slapadd is much
+faster
+* Does not provide faster or more scalable write performance (neither could
+ any Multi-Master solution)
+* Backups are managed slightly differently
+- If backing up the Berkeley database itself and periodically backing up the
+transaction log files, then the same member of the mirror pair needs to be
+used to collect logfiles until the next database backup is taken
+- To ensure that both databases are consistent, each database might have to be
+put in read-only mode while performing a slapcat.
+- When using slapcat, the generated LDIF files can be rather large. This can
+happen with a non-MirrorMode deployment also.
+
+H3: MirrorMode Configuration
+
+MirrorMode configuration is actually very easy. If you have ever setup a normal
+slapd syncrepl provider, then the only change is the directive:
+
+> mirrormode on
+
+You also need to make you the {{rid}} of each mirror node pair is different and
+that the {{provider}} syncrepl directive points to the other mirror pair.
+
+H4: Mirror Node Configuration
+
+This is the same as the {{SECT:Set up the provider slapd}} section, referencing
+{{SECT:delta-syncrepl replication}} if using {{delta-syncrepl}}.
+
+Here's a specific cut down example using {{SECT:LDAP Sync Replication}} in
+{{refreshAndPersist}} mode ({{delta-syncrepl}} can be used also):
+
+MirrorMode node 1:
+
+> # syncrepl directives\r
+> syncrepl rid=1\r
+> provider=ldap://ldap-rid2.example.com\r
+> bindmethod=simple\r
+> binddn="cn=mirrormode,dc=example,dc=com"\r
+> credentials=mirrormode\r
+> searchbase="dc=example,dc=com"\r
+> schemachecking=on\r
+> type=refreshAndPersist\r
+> retry="60 +"\r
+> \r
+> mirrormode on
+
+MirrorMode node 2:
+
+> # syncrepl directives\r
+> syncrepl rid=2\r
+> provider=ldap://ldap-rid1.example.com\r
+> bindmethod=simple\r
+> binddn="cn=mirrormode,dc=example,dc=com"\r
+> credentials=mirrormode\r
+> searchbase="dc=example,dc=com"\r
+> schemachecking=on\r
+> type=refreshAndPersist\r
+> retry="60 +"\r
+> \r
+> mirrormode on
+
+It's simple really; each MirrorMode node is setup {{B:exactly}} the same, except
+that the {{B:provider}} directive is set to point to the other MirrorMode node.
+
+H4: Failover Configuration
+
+There are generally 2 choices for this; 1. Hardware proxies/load-balancing or
+dedicated proxy software, 2. using a Back-LDAP proxy as a syncrepl provider
+
+MORE HERE and a nice PICTURE
+
+
+H4: Normal Consumer Configuration
+
+This is exactly the same as the {{SECT:Set up the consumer slapd}} section. It
+can either setup in normal {{SECT:syncrepl replication}} mode, or in
+{{SECT:delta-syncrepl replication}} mode.
+
+H3: MirrorMode Summary
+
+Hopefully you will now have a directory architecture that provides all of the
+consistency guarantees of single-master replication, whilst also providing the
+high availability of multi-master replication.
+
projects / openldap / blobdiff