Citrix Systems 4.2 manual About Global Server Load Balancing, Components of Gslb

Global Server Load Balancing

You can delete or modify existing health check policies.

To configure how often the health check is performed by default, use the global configuration setting healthcheck.update.interval (default value is 600 seconds). You can override this value for an individual health check policy.

For details on how to set a health check policy using the UI, see Section 16.8.1, “Adding a Load Balancer Rule”.

16.9. Global Server Load Balancing

CloudPlatform supports Global Server Load Balancing (GSLB) functionalities to provide business continuity by load balancing traffic to an instance on active zones only in case of zone failures. CloudPlatform achieves this by extending its functionality of integrating with NetScaler Application Delivery Controller (ADC), which also provides various GSLB capabilities, such as disaster recovery and load balancing. The DNS redirection technique is used to achieve GSLB in CloudPlatform.

In order to support this functionality, region level services and service provider are introduced. A new service 'GSLB' is introduced as a region level service. The GSLB service provider is introduced that will provider the GSLB service. Currently, NetScaler is the supported GSLB provider in CloudPlatform. GSLB functionality works in an Active-Active data center environment.

16.9.1. About Global Server Load Balancing

Global Server Load Balancing (GSLB) is an extension of load balancing functionality, which is highly efficient in avoiding downtime. Based on the nature of deployment, GSLB represents a set of technologies that is used for various purposes, such as load sharing, disaster recovery, performance, and legal obligations. With GSLB, workloads can be distributed across multiple data centers situated at geographically separated locations. GSLB can also provide an alternate location for accessing a resource in the event of a failure, or to provide a means of shifting traffic easily to simplify maintenance, or both.

16.9.1.1. Components of GSLB

A typical GSLB environment is comprised of the following components:

•GSLB Site: In CloudPlatformterminology, GSLB sites are represented by zones that are mapped to data centers, each of which has various network appliances. Each GSLB site is managed by a NetScaler appliance that is local to that site. Each of these appliances treats its own site as the local site and all other sites, managed by other appliances, as remote sites. It is the central entity in a GSLB deployment, and is represented by a name and an IP address.

•GSLB Services: A GSLB service is typically represented by a load balancing virtual server in a zone. In a GSLB environment, you can have a local as well as remote GSLB services. A local GSLB service represents a local load balancing or content switching virtual server. A remote GSLB service is the one configured at one of the other sites in the GSLB setup. At each site in the GSLB setup, you can create one local GSLB service and any number of remote GSLB services.

•GSLB Virtual Servers: A GSLB virtual server refers to a logical grouping of one or more GSLB services. CloudPlatform GSLB functionality ensures that traffic is load balanced across VMs in multiple zones. It evaluates the configured GSLB methods or algorithms to select a GSLB service to which to send the client requests. One or more virtual servers from different zones are bound to the GSLB virtual server. GSLB virtual server does not have a public IP associated with it, instead it will have a FQDN DNS name.

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