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&PRODUCT; supports Global Server Load Balancing (GSLB) functionalities to provide business continuity, and enable seamless resource movement within a &PRODUCT; environment. &PRODUCT; achieve 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 &PRODUCT;. In order to support his 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 &PRODUCT;. GSLB functionality works in an Active-Active data center environment.

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.

The GSLB functionality is supported both Basic and Advanced zones. GSLB is added as a new network service. GSLB service provider can be added to a physical network in a zone. The admin is allowed to enable or disable GSLB functionality at region level. The admin is allowed to configure a zone as GSLB capable or enabled. A zone shall be considered as GSLB capable only if a GSLB service provider is provisioned in the zone. When users have VMs deployed in multiple availability zones which are GSLB enabled, user is allowed to use the GSLB functionality to load balance traffic across the VMs in multiple zones. The users are allowed to use GSLB to load balance across the VMs across zones in a region only if the admin has enabled GSLB in that region. The users are allowed to load balance traffic across the availability zones in the same region or different regions. The admin is allowed to configure DNS name for the entire cloud. The users can specify an unique name, across the cloud, for a globally load balanced service. The provided name will be used as the domain under the DNS name associated with the cloud. The user-provided name along with the admin-provided DNS name is used to produce a globally resolvable FQDN for the globally load balanced service of the user. For example, if the admin has configured xyztelco.com as the DNS name for the cloud, and user specifies 'foo' for the GSLB virtual service, then the FQDN name of the GSLB virtual service is foo.xyztelco.com. While setting up GSLB, users can select a load balancing method, such as round robin or least RTT, that would be the load balance traffic used across the zones that are part of GSLB. The user shall be able to set weight to zone-level virtual server. Weight shall be considered by the load balancing method is distributing the traffic. The GSLB functionality shall support session persistence, where series of client requests for particular domain name is sent to a virtual server on the same zone. Statistics is collected from each GSLB virtual server.

Log in to the &PRODUCT; UI as administrator. In the left navigation pane, click Region. Select the region for which you want to create a GSLB rule. In the Details tab, click View GSLB. Click Add GSLB. The Add GSLB page is displayed as follows: gslb-add.png: adding a gslb rule Specify the following: Name: Name for the GSLB rule. Description: (Optional) A short description of the GSLB rule that can be displayed to users. GSLB Domain Name: A preferred domain name for the service. Algorithm: (Optional) The algorithm to use to load balance the traffic across the zones. The options are Round Robin, Least Connection, and Proximity. Service Type: The transport protocol to use for GSLB. The options are TCP and UDP. Domain: (Optional) The domain for which you want to create the GSLB rule. Account: (Optional) The account on which you want to apply the GSLB rule. Click OK to confirm.

The following is an illustrated conceptual model of how GLSB functionality is provided in &PRODUCT;: An organization, xyztelco, has set up a public cloud that spans two zones, Zone-1 and Zone-2, across geographically separated data centers that are managed by &PRODUCT;. Tenant-A of the cloud launches a highly available solution by using xyztelco cloud. For that purpose, they launch two instances each in both the zones: VM1 and VM2 in Zone-1 and VM5 and VM6 in Zone-2. Tenant-A acquires a public IP, IP-1 in Zone-1, and configures a load balancer rule to load balance the traffic between VM1 and VM2 instances. &PRODUCT; orchestrates setting up a virtual server on the LB service provider in Zone-1. Virtual server 1 that is set up on the LB service provider in Zone-1 represents a publicly accessible virtual server that client reaches at IP-1. The client traffic to virtual server 1 at IP-1 will be load balanced across VM1 and VM2 instances. Tenant-A acquires another public IP, IP-2 in Zone-2 and sets up a load balancer rule to load balance the traffic between VM5 and VM6 instances. Similarly in Zone-2, &PRODUCT; orchestrates setting up a virtual server on the LB service provider. Virtual server 2 that is setup on the LB service provider in Zone-2 represents a publicly accessible virtual server that client reaches at IP-2. The client traffic that reaches virtual server 2 at IP-2 is load balanced across VM5 and VM6 instances. At this point Tenant-A has the service enabled in both the zones, but has no means to set up a disaster recovery plan if one of the zone fails. Additionally, there is no way for Tenant-A to load balance the traffic intelligently to one of the zones based on load, proximity and so on. The cloud administrator of xyztelco provisions a GSLB service provider to both the zones. A GSLB provider is typically an ADC that has the ability to act as an ADNS (Authoritative Domain Name Server) and has the mechanism to monitor health of virtual servers both at local and remote sites. The cloud admin enables GSLB as a service to the tenants that use zones 1 and 2. gslb.png: GSLB architecture Tenant-A wishes to leverage the GSLB service provided by the xyztelco cloud. Tenant-A configures a GSLB rule to load balance traffic across virtual server 1 at Zone-1 and virtual server 2 at Zone-2. The domain name is provided as A.xyztelco.com. &PRODUCT; orchestrates setting up GSLB virtual server 1 on the GSLB service provider at Zone-1. &PRODUCT; binds virtual server 1 of Zone-1 and virtual server 2 of Zone-2 to GLSB virtual server 1. GSLB virtual server 1 is configured to start monitoring the health of virtual server 1 and 2 in Zone-1. &PRODUCT; will also orchestrate setting up GSLB virtual server 2 on GSLB service provider at Zone-2. &PRODUCT; will bind virtual server 1 of Zone-1 and virtual server 2 of Zone-2 to GLSB virtual server 2. GSLB virtual server 2 is configured to start monitoring the health of virtual server 1 and 2. &PRODUCT; will bind the domain A.xyztelco.com to both the GSLB virtual server 1 and 2. At this point, Tenant-A service will be globally reachable at A.xyztelco.com. The private DNS server for the domain xyztelcom.com is configured by the admin out-of-band to resolve the domain A.xyztelco.com to the GSLB providers at both the zones, which are configured as ADNS for the domain A.xyztelco.com. A client when sends a DNS request to resolve A.xyztelcom.com, will eventually get DNS delegation to the address of GSLB providers at Zone 1 and 2. A client DNS request will be received by the GSLB provider. The GSLB provider, depending on the domain for which it needs to resolve, will pick up the GSLB virtual server associated with the domain. Depending on the health of the virtual servers being load balanced, DNS request for the domain will be resolved to the public IP associated with the selected virtual server.

Currently, &PRODUCT; does not support orchestration of services across the zones. The notion of services and service providers in region are to be introduced.