The primary goal of the Global Traffic Manager is to ensure that name resolution requests are sent to the best available resource on the network. Consequently, it is typical for multiple Global Traffic Managers to reside in several locations within a network. For example, a standard installation might include a Global Traffic Manager at each data center within an organization.
When a Local Domain Name Server (LDNS) submits a name resolution request, you cannot control to which Global Traffic Manager the request is sent. As a result, you will often want multiple Global Traffic Managers to share the same configuration values, and maintain those configurations over time. This process is called synchronization.
In network configurations that contain more than one Global Traffic Manager, synchronization means that each Global Traffic Manager regularly compares the timestamps of its configuration files with each other. If, at any time, a system discovers that its configuration files are too old, it will automatically transfer the newest configuration files to itself. With synchronization, you can change settings on one system and have that change distributed to all other systems.
You can separate the Global Traffic Managers on your network into separate groups, called synchronization groups. A synchronization group is a collection of multiple Global Traffic Managers that share and synchronize configuration settings. These groups are identified by a synchronization group name, and only systems that share this name will share configuration settings. These synchronization groups allow you to customize the synchronization behavior. For example, the Global Traffic Managers residing in data centers in Europe might belong to one synchronization group, while the systems in North America belong to another group.
The following sections provide additional information on synchronization and the Global Traffic Manager, and specifically covers the following topics:
Before you can synchronize Global Traffic Managers, you must define the the Network Time Protocol (NTP) servers that the Global Traffic Manager references. These servers ensure that each Global Traffic Manager is referencing the same time when verifying timestamps for configuration files.
Repeat this process for any additional time servers.
Activating synchronization for the Global Traffic Manager has an immediate affect on its configurations, provided that another Global Traffic Manager is already available on the network. We recommend that you activate synchronization after you have finished configuring one of the systems.
When you opt to synchronize multiple Global Traffic Managers, you are instructing each system to share its configuration files with the other systems on the network. These files are synchronized based on their timestamp: if a Global Traffic Manager determines that its configuration files are older than those on another system, it acquires the newer files and begins using them to load balance name resolution requests.
You can control the synchronization by defining the maximum age difference between two sets of configuration files. This value is referred to as synchronization time tolerance.
By default, the value for the synchronization time tolerance is set to 10 seconds. The minimum value you can set for this value is 5 seconds, while the maximum you can set is 600 seconds.
In the event that you need to deactivate file synchronization, you can do so at any time. Situations in which you want to disable synchronization include updating the data center in which the Global Traffic Manager resides, or when you are testing a new configuration change.
During synchronization operations, the Global Traffic Manager verifies that it has the latest configuration files available and, if it does not, the Global Traffic Manager downloads the newer files from the appropriate system. You can expand the definition of the configuration files to include the DNS zone files used to respond to name resolution requests by using the Synchronize DNS Zone Files option. This option is enabled by default.
Each Global Traffic Manager that you synchronize must belong to a specific group of systems, called a synchronization group. A synchronization group is a collection of multiple Global Traffic Managers that share and synchronize configuration settings. Initially, when you enable synchronization for a Global Traffic Manager, the system belongs to a synchronization group called default. However, you can create new groups at any time. This process allows you to customize the synchronization process, ensuring that only certain sets of Global Traffic Managers share configuration values.
To illustrate how synchronization groups work, consider the fictional company, SiteRequest. SiteRequest has decided to add a new data center in Los Angeles. As part of bringing this data center online, SiteRequest has decided that it wants the Global Traffic Managers installed in New York and in Los Angeles to share configurations, and the Paris and Tokyo data centers to share configurations. This setup exists because SiteRequest's network optimization processes require slightly different settings within the United States than the rest of the world. To accommodate this new network configuration, SiteRequest enables synchronization for the New York and Los Angeles data centers, and assigns them a synchronization group name of United States. The remaining data centers are also synchronized, but with a group name of Rest Of World. As a result, a configuration change at the Paris Global Traffic Manager immediately modifies the Tokyo system, but does not affect the systems in the United States.