Tuesday, January 13, 2015

Quick note on OpenAM CTS stores

The following is extracted from OpenAM documentation (nightly maybe), but important:

  • Prevent random or round-robin load balancing to external CTS stores. 
  • No load balancer is needed between OpenAM and an external CTS store. Instead configure multiple directory server replicas in the Connection Strings of the configuration. 
  • When OpenAM writes to a directory server in the external CTS store, directory server replication pushes the write to other directory servers in the same replication group. When under load operations in an OpenAM server can happen more quickly than the network can push replication updates. Therefore, balancing the LDAP traffic from OpenAM to the CTS store in random or round robin fashion leads to errors where a read operation arrives at a replica before the expected write operation can cross the network
  • For complex deployments you might opt for an external directory service as the CTS store with a load balancer between OpenAM and the directory service. In this case, the choice of load balancing algorithm is important to ensure consistency under load within the CTS layer. High loads with a round-robin or random algorithm cause replication conflicts within the CTS layer, which the CTS layer is unable to resolve. The load balancer must operate only for failover, and not to balance LDAP traffic between directory servers. In other words, the load balancer in front of the external CTS store must use an Active/Passive configuration, whereby the load balancer sends all requests to the same directory server until that server becomes unavailable, and then all requests go to the standby directory server, and so on. Load balancers must not use an Active/Active configuration, as this leads to the type of errors described above.


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