Redundancy at the Hardware Level

This section provides basic information about hardware redundancy. Many publications provide comprehensive information about using hardware redundancy for high availability. In particular, see “Blueprints for High Availability” published by John Wiley & Sons, Inc.

Hardware SPOFs can be broadly categorized as follows:

• Network failures

• Failure of the physical servers on which Directory Server or Directory Proxy Server are running

• Load balancer failures

• Storage subsystem failures

• Power supply failures

Failure at the network level can be mitigated by having redundant network components. When designing your deployment, consider having redundant components for the following:

• Internet connection

• Network interface card

• Network cabling

• Network switches

• Gateways and routers

You can mitigate the load balancer as an SPOF by including a redundant load balancer in your architecture.

In the event of database corruption, you must have a database failover strategy to ensure availability. You can mitigate against SPOFs in the storage subsystem by using redundant server controllers. You can also use redundant cabling between controllers and storage subsystems, redundant storage subsystem controllers, or redundant arrays of independent disks.

If you have only one power supply, loss of this supply could make your entire service unavailable. To prevent this situation, consider providing redundant power supplies for hardware, where possible, and diversifying power sources. Additional methods of mitigating SPOFs in the power supply include using surge protectors, multiple power providers, and local battery backups, and generating power locally.

Failure of an entire data center can occur if, for example, a natural disaster strikes a particular geographic region. In this instance, a well-designed multiple data center replication topology can prevent an entire distributed directory service from becoming unavailable. For more information, see Using Replication and Redundancy for High Availability.