| 摘要 |
A trigger is provided in association with a network naming service, such as DNS (Domain Name Service), that handles client requests for an application. The trigger comprises a set of executable instructions referenced by a resource record associated with an identifier of the application. In response to a client request concerning the application, the resource record is retrieved and the instructions are executed. In one implementation of a trigger, a DNS server provides load balancing among a plurality of serves within a network name space (e.g., domain or sub-domain) offering an application program (or replicated service) that is known by a virtual server name. A policy is selected for choosing a preferred server from the plurality of servers according to a specified status or operational characteristic of the application instances, such as the least-loaded instance of the application or the instance with the fastest response time. The policy is encapsulated within multiple levels of objects or modules distributed among the plurality of servers and the DNS server. The objects collect and assemble the servers' status and operational characteristics. The information collected by the objects is analyzed to select the server that best satisfies the selected policy. A client request for the application is received by the DNS server, which retrieves a resource record corresponding to the virtual server name. Within the record is the name of a trigger. The trigger is executed to select, or retrieve an identity of, a server to which the client request is to be directed.
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