The master directory server must provide reliable replication to the replica systems. OpenLDAP currently provides three methods for replicating that data, each with its pros and cons.

Replication types

• slurpd – A push-based method of replication
• syncrepl – A pull-based or push-based method of replication
• delta-syncrepl – Another pull-based method of replication, using slapo-accesslog and syncrepl

slurpd replication

Slurpd is the oldest of the replication mechanisms. It allows the master to connect to replicas and push changes.

Pros

• Proven track record for reliability
• Allows master->client replication when there is a firewall preventing the replicas from initiating connections to the master.
• Data updates are minimal (ADD, DEL, or deltas for MOD)

Cons

• Not actively developed
• Minimally configurable
• Requires a secondary process for replication (slurpd)
• Does not support replica catch-up

syncrepl replication

Syncrepl is the newest form of replication. It allows replica servers to connect to the master to pull changes.

Pros

• Highly configurable
• Actively developed
• Allows master->client replication when the master is behind a firewall that prevents it from opening connections to a replica
• Supports replica catch-up if the replicas database is older than the masters
• Replication does not require a separate process
• Can be used with back-ldap to implement push-based replication

Cons

• Data updates are maximal (ADD, DEL, or a full set of MODs for all existing attributes)

delta-syncrepl replication

Delta-Syncrepl is an extension of syncrepl, and uses the accesslog overlay to track changes that need replicating.

Pros

• Highly configurable
• Actively developed
• Allows master->client replication when the master is behind a firewall that prevents it from opening connections to a replica
• Supports replica catch-up if the replicas database is older than the masters
• Replication does not require a separate process
• Data updates are minimal (ADD, DEL, or deltas for MOD)

Cons

• Updates are serialized. If there are multiple processes that update the master, updates will be very slow.