A GSLB service is the representation of a global application. It acts as a front end for instantiations of the application that are deployed at multiple sites.

The following are key elements of a global service:

  • Global application service name: The name by which administrators reference the GSLB configuration.

  • Application FQDN: Used by the end user clients to reference the global service. A list of domain names can be provided for aliasing, for example, www.foo.com and foo.com.

  • Applications running in various GSLB sites, organized into one or more GSLB pools: An application is usually hosted as a virtual service on NSX Advanced Load Balancer. However, it can also be the virtual service of a third-party ADC or an IP:port on a standalone server.

    Note:

    A GSLB pool is different from a server pool. The former aggregates backing services, while the latter aggregates servers.

  • Health Monitoring: For more information on health monitors, see Health Monitoring in the VMware NSX Advanced Load Balancer Configuration Guide.

  • A time-to-live (TTL) ranging from 1-86400 seconds: This value determines the frequency with which clients need to obtain fresh steering information for client requests. If no TTL value is specified for a particular GSLB service, the value defaults to the one specified in the DNS application profile (default value is 30 seconds).

  • Support for load balancing algorithms.

  • Support for deployment models like Active-Active and Active-Standby.

Note:

It is recommended to use caution when using very low values of TTL since some DNS or operating systems discard a very low TTL.

DNS Response when GSLB Service is Down

When a GSLB service pool member (that is, some participating virtual service) is down, the GSLB DNS returns one of four standard responses. In the GslbService object, set the GslbService.down_response parameter to select one of these following:

GSLB_SERVICE_DOWN_RESPONSE_NONE

The default option, simply drops the request.

GSLB_SERVICE_DOWN_RESPONSE_FALLBACK_IP

Respond with a single preset fallback IP address, which typically would point to an error page.

GSLB_SERVICE_DOWN_RESPONSE_ALL_RECORDS

Return all IP addresses of all members of all pools.

It is recommended to use this option because, if the GSLB service goes down, all IP addresses are returned to the client, and the client can choose the IP address as required.

GSLB_SERVICE_DOWN_RESPONSE_EMPTY

Return an empty DNS response. It can be used to make the client retry in certain cases.