In the architecture shown here, a large financial institution has its headquarters in London. The organization has data centers in London, New York, and Hong Kong. Currently, the vast majority of the data that is available to employees resides centrally in legacy RDBMS repositories in London. All access to this data from the financial institution’s client community is over the WAN.
The organization is experiencing scalability and performance problems with this centralized model and decides to move to a distributed data model. The organization also decides to deploy an LDAP directory infrastructure at the same time. Because the data in question is considered “mission critical” it must be deployed in a highly available, fault-tolerant infrastructure.
An analysis of client application profiles has revealed that the data is customer-based. Therefore, 95 percent of the data accessed by a geographical client community is specific to that community. Clients in Asia rarely access data for a customer in North America, although this does happen infrequently. The client community must also update customer information from time to time.
The following figure shows the logical architecture of the distributed solution.
Given the profile of 95 percent local data access, the organization decides to distribute the directory infrastructure geographically. Multiple directory consumers are deployed in each geographical location: Hong Kong, New York, and London. London consumers are not shown in the diagram for ease of understanding. Each of these consumers is configured to hold the customer data specific to the location. Data for European and Middle East customers is held in the London consumers. Data for North and South American customers is held in the New York consumers. Data for Asian and Pacific Rim customers is held in the Hong Kong consumers.
With this deployment, the overwhelming data requirement of the local client community is located in the community. This strategy provides significant performance improvements over the centralized model. Client requests are processed locally, reducing network overhead. The local directory servers effectively partition the directory infrastructure, which provides increased directory server performance and scalability. Each set of consumer directory servers is configured to return referrals if a client submits an update request. Referrals are also returned if a client submits a search request for data that is located elsewhere.
Client LDAP requests are sent to Directory Proxy Server through a hardware load balancer. The hardware load balancer ensures that clients always have access to at least one Directory Proxy Server. The locally deployed Directory Proxy Server initially routes all requests to the array of local directory servers that hold the local customer data. The instances of Directory Proxy Server are configured to load balance across the array of directory servers. This load balancing provides automatic failover and failback.
Client search requests for local customer information are satisfied by a local directory. Appropriate responses are returned to the client through Directory Proxy Server. Client search requests for geographically “foreign” customer information are initially satisfied by the local directory server by returning a referral back to Directory Proxy Server.
This referral contains an LDAP URL that points to the appropriate geographically distributed Directory Proxy Server instance. The local Directory Proxy Server processes the referral on behalf of the local client. The local Directory Proxy Server then sends the search request to the appropriate distributed instance of Directory Proxy Server. The distributed Directory Proxy Server forwards the search request on to the distributed Directory Server and receives the appropriate response. This response is then returned to the local client through the distributed and the local instances of Directory Proxy Server.
Update requests received by the local Directory Proxy Server are also satisfied initially by a referral returned by the local Directory Server. Directory Proxy Server follows the referral on behalf of the local client. However, this time the proxy forwards the update request to the supplier directory server located in London. The supplier Directory Server applies the update to the supplier database and sends a response back to the local client through the local Directory Proxy Server. Subsequently, the supplier Directory Server propagates the update down to the appropriate consumer Directory Server.