I have a single data center; do I need GTM?

Short answer

GTM is not needed to distribute traffic among the servers in the data center; this is the job of Load Balancer - ADC. Even in a single data center, GTM works in the Standalone mode and is useful for these needs: managing domain names on TR7 as authoritative DNS, removing the unhealthy address from the answer if the same service is reachable at more than one address, and directing the user to another address (e.g. a maintenance page) with Fail-Safe Records when no healthy address remains at all. When a second data center is added, the same domain is switched to the Disaster Recovery or Datacenter mode.

How Does It Work?

In the Standalone mode, the domain has a single data center group (the local data center). The HC condition of each address in the record is selected as Static, Disabled or a health scenario:

1. An address bound to a scenario is included in the answer while the scenario is active, and is removed from the answer otherwise.
2. The remaining addresses are returned according to the record's Balance Algorithm.
3. If no address remains at all, Fail-Safe Records are returned, if defined.

What Is It For?

Need	Without GTM	With GTM (Standalone)
Distribution among servers	Load Balancer	Load Balancer (GTM is not needed)
DNS of the domain name	A separate DNS server	TR7 answers as authoritative DNS
The service is reachable at more than one address	Even if one of the addresses does not respond, DNS keeps giving it	The address whose scenario is passive is removed from the answer
None of the service's addresses is healthy	DNS keeps giving the same addresses	The fail-safe address (e.g. a maintenance page in the cloud) is returned

In TR7

• When a domain is added, Default Mode comes as Standalone by default; in this mode there is no data center selection, and no Remote Devices definition is needed.
• Fail-Safe Records are useful as long as TR7's DNS Service can answer; against the data center becoming entirely unreachable, the Disaster Recovery or Datacenter mode is set up with a TR7 in a second data center.
• The other data center in the Disaster Recovery and Datacenter modes is another TR7 device added to Remote Devices. If the backup target is outside TR7 (e.g. a cloud address), Fail-Safe Records are used in the Standalone mode.

Common Misconceptions

• "GTM balances load among servers." GTM selects the addresses in the answer; connection-level distribution to the servers in the same data center is done with the Load Balancer (What is the difference between GTM and the Load Balancer?).
• "The fail-safe address is also monitored with a health check." Fail-Safe Records are not bound to a health condition; they are returned only when no candidate address remains (What is fail-safe; what does GTM answer if no address is healthy?).
• "Standalone means only static DNS." By binding the addresses to a health scenario, health-aware answers are given even in a single data center.

How it is done in the documentation

• Domains · Standalone
• GTM (Global Traffic Manager) · Use Cases
• Records · Fail-Safe Records

Related questions

• Can I use GTM only as an authoritative DNS server?
• What is the difference between the Standalone, Disaster Recovery and Datacenter modes?
• What is the difference between Load Balancer and GTM; which one should I use?