To use GTM, you need to configure access policies for different users in order to provide user-specific service. An access policy involves DNS resolution based on location and address pool failover.
You can configure multiple access policies for an instance to enable failover and allow users in different regions to access the nearest application service.
To configure an access policy, specify the following information:
Set an access policy name that is easy to remember and recognize.
A default address pool is one that users use to access application services in normal cases. You can select an address pool from the drop-down list as the default address pool.
When the default address pool is unavailable because multiple IP addresses are faulty, the access policy switches to a failover address pool. Select an address pool from the drop-down list as the failover address pool.
Region where the users corresponding to the current access policy is located:
- Global: All the access users by default.
- ISP: ISP for the access users. With an ISP selected, if DNS matches the users of the ISP, it returns the corresponding address pool; if no match is found, DNS returns the global settings.
- Mainland China: Region for the access users. You can configure different address pools for users in different regions. If DNS matches the users in a specific region, it returns the corresponding address pool; if no match is found, DNS returns the global settings. This option and ISP are mutually exclusive.
- Overseas regions: Continent where access users outside Mainland China are located. You can configure different address pools for users in different continents. If DNS matches the users in a specific continent, it returns the corresponding address pool; if no match is found, DNS returns the global settings.
After an access policy is created, the system generates a corresponding DNS record. The access status indicates the address pool accessed by a specific user. By default, information about the default address pool is displayed if this address pool is normal; if it is abnormal, information about the failover address pool is displayed.
The status of an address pool is determined by the number of available IP addresses in the address pool. The address pool is available when the number of its available IP addresses is greater than or equal to the value of Minimum Available Addresses; otherwise, the address pool is unavailable.
By default, the Auto Switch policy is used, which switches between the default and failover address pool based on the pool status. If address pool switchover does not meet your expectation, you can manually adjust the access policy to your expected address pool.