Handout CNAMEs

In a property's configuration, you can optionally enter a handout CNAME for each data center. When you make a query for such a property, GTM determines to which data center you should be mapped. If that data center has a handout CNAME configured, the answer returned is the handout CNAME, rather than the servers that might be configured for the data center.

Handout CNAMEs are most often used with autonomous system (AS) maps, CIDR maps, and geographically mapped properties, but they can be used with any type of property.

When you specify a Handout CNAME, traffic distributed to this Traffic Target is sent to the data center to which the CNAME is mapped. If you specify servers as well as a Handout CNAME, Liveness Test results from these servers are used to determine if this Traffic Target is available. If you do not specify a server, this Traffic Target is considered always available.

If you set the server name and the Handout CNAME to the same hostname, GTM returns a warning message indicating that this operation is risky and ill-advised. In this scenario, if the hostname resolves to several IP addresses, and half of the IP addresses are down, GTM will do the following:
  • If you use a handout CNAME, then GTM returns the CNAME to the client, who then resolves it, giving GTM a 50% chance of accessing a server that is down.
  • If you do not use a handout CNAME, then GTM returns only the IP addresses that are up (live).

We recommend that you avoid setting the server name and the Handout CNAME to the same hostname.