Introduction to Load Balancing

Directory Proxy Server distributes requests according to a load balancing algorithm. The following load balancing algorithms can be configured:

Proportional algorithm

Requests are distributed according to the weight of the data source and the cumulative load of the data source since the last startup of Directory Proxy Server.

Saturation algorithm

Requests are distributed according to the weight of the data source and the number of available connections on the data source.

Operational affinity algorithm

Requests are distributed according to the hash value. The number of hash values that are allocated to an attached data source is proportional to the weight of that data source.

Failover algorithm

Requests are distributed exclusively to the attached data source with the highest weight for that operation.

In all load balancing algorithms, each attached data source can be configured with an independent weight for each of the following types of operation:

• Add

• Bind

• Compare

• Delete

• Modify DN

• Modify

• Search

If multiple attached data sources are configured with the same weight for a given type of operation, Directory Proxy Server distributes the requests evenly between the data sources. If a data source has a weight of disabled for a particular type of operation, Directory Proxy Server never distributes requests of that type to the data source. If a data source has a weight of 0 (zero) no requests are distributed to that data source unless all other data sources are unavailable. Therefore, data sources configured with a weight of 0 are used only when all other data sources are down.

An attached data source cannot be selected by the load balancing algorithm in the following circumstances:

• The data source is unavailable because an error occurred.

• All connections between the Directory Proxy Server and the data source are in use.

If a data source is configured as read-only, the data source cannot receive add, delete, or modify requests. The data source can receive search requests.

The load balancing algorithm works on a best-effort basis. If there are not sufficient resources for the load balancing algorithm to distribute requests by respecting weights, the weights are overruled. For example, if the number of simultaneous requests to a data source exceeds the maximum number of connections to that data source, requests are distributed to other data sources.

When the client affinity feature is active, Directory Proxy Server distributes requests by using the client affinity feature instead of using the load balancing algorithm. For information about client affinity, see Client Affinity.