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Features

Last Updated: Jan 25, 2021

This topic describes the core features of Global Traffic Manager (GTM).

Configure GTM

You can configure basic settings and an access policy when you create a GTM instance. The basic settings include the instance name, canonical domain name, service domain name, global time-to-live (TTL), alert contact group, and alert notification method. The access policy can be created based on geographic locations or latency.

1 . Access policy types

(1) Access policy based on geographical locations

Users in various regions can access services from the nearest access points. This way, network access is accelerated.

(2) Access policy based on latency

GTM detects the access latency between the location of a user and the region in which the application is deployed. Then, GTM routes user requests to the application server cluster that has the lowest latency. This policy is available only to the users of GTM Ultimate Edition.

2 . Basic settings

(1) Canonical domain name (for the Internet)

GTM provides the traffic scheduling service by using CNAME records. In the Alibaba Cloud DNS console, you can create a CNAME record to map a service domain name to a canonical domain name that is provided by GTM. Canonical domain names have the following two types. You can change the types in the global settings.

  • System-assigned canonical domain name: You can select this option if all addresses in the address pool are hosted by Alibaba Cloud.

  • Custom canonical domain name: You can use a domain name of your account as the suffix of a GTM canonical domain name. We recommend that you select this option if your domain name is hosted by a data center.

(2) Load balancing policy

The following two types of load balancing policies are available: Return all addresses and Return addresses by weight.

  • Return all addresses: If multiple IP addresses exist in the address pool, access traffic is evenly distributed to each IP address. This policy is used by default.

  • Return addresses by weight: After a DNS request is sent, GTM returns an IP address based on a preset weight. This way, access traffic is distributed based on address weights.

(3) Global TTL

A global TTL indicates the period for which an IP address that corresponds to a domain name can be cached on a DNS server. If you use a canonical custom domain name, the global TTL must be the same as the minimum TTL that is specified in the DNS package for the domain name.

(4) Service domain name (for the Internet)

A service domain name is use to access an application service. Make sure that you specify a valid service domain name. To implement traffic scheduling, you must use a CNAME record to map a service domain name to a GTM canonical domain name in the Alibaba Cloud DNS console.

(5) Alert contact group

An alert contact group is used to receive notifications if errors occur. You can configure an alert contact group in Cloud Monitor. If the health check feature of GTM detects a problem, for example, an IP address is abnormal or an address pool is unavailable, GTM sends an alert notification to the corresponding contact group.

(6) Alert notification method

You can use emails and text messages to send alert notifications. You can set notification methods based on alert event types.

Configure address pools

Address pools allow you to manage IP addresses for the same application service by group. For example, you can assign IP addresses in different regions to different address pools. This allows you to use the health check and fault isolation features with ease. You can set a working mode and weight for each IP address in an address pool. You can also set the address pool type.

1. Address pool types

  • If you use the access policy based on geographical locations, you can set the Address Pool Type parameter to IPv4, IPv6, or Domain Name.

  • If you use the access policy based on latency, you can set the address pool type to IPv4.

2. Region

After you specify an address in an address pool, GTM automatically displays the geographical location of the application service. You can also click Modify to modify the geographical location of the application service.

Note

If the Address Pool Type parameter is set to Domain Name, you must modify the location.

3. Address working mode

In an address pool, you can set the following working modes for addresses:

  • Smart Return: This mode is used by default. GTM determines whether to return an IP address based on the health check result. If the IP address is available, DNS returns the IP address to clients. If the IP address is unavailable, GTM deletes the IP address.

  • Always Online: In this mode, GTM determines that an address is always available and DNS always returns the address to clients. The health check feature does not check the address. To provide services in an unstable network environment, you can set the Mode parameter of an address to Always Online.

  • Always Offline: In this mode, GTM determines that an address is always unavailable and DNS does not return the address to clients. This address is configured in the system settings for future use. The health check feature does not check the address. To upgrade a cluster, you can set the Mode parameter of an address to Always Offline.

4. Address weight

You can set a weight for each IP address in the address pool. After a DNS request is sent, GTM returns an IP address based on the preset weight. This way, access traffic is distributed based on address weights. You can set load balancing policies for address pools and addresses.

Load balancing policies

Address pool

Address

Supported

Return addresses by weight

Return addresses by weight

Yes

Return all addresses

Return addresses by weight

No. The Return addresses by weight policy that is specified for addresses does not take effect. The Return all addresses policy that is specified for the address pool is used.

Return all addresses

Return all addresses

Supported

Return addresses by weight

Return all addresses

No. The Return all addresses policy that is specified for addresses does not take effect. The Return addresses by weight policy that is specified for the address pool is used.

Note

If you use the access policy based on latency, you cannot specify load balancing policies.

Weight calculation rules:

If both the load balancing policies of an address pool and an address are set to Return addresses by weight, the final weight of the address is obtained by multiplying the weight of the address pool and the weight of the address.

The following table shows an example of weight settings. In this example, the weight of the IP address 1.1.1.1 is: 2 × 4 = 8.

Address pool

PoolA

PoolB

Address pool weight

4

2

Address

1.1.1.1

2.2.2.2

Address weight

2

3

The following table shows another example of weight settings. The IP address 1.1.1.1 exists in both Pool A and Pool B. In this example, the weight of the IP address 1.1.1.1 is: 2 × 4 + 1 × 1 = 9.

Address pool

PoolA

PoolB

Address pool weight

4

1

Address

1.1.1.1

2.2.2.2

1.1.1.1

3.3.3.3

Address weight

2

3

1

3

Access policies

1. Access policy based on geographical locations

(1) DNS Request Sources

You can specify DNS request sources to achieve intelligent DNS resolution. When you select a region, users in this region can access the application service by using the address pool that is configured for the access policy. In this example, select Global. The Global option indicates that the access policy applies to all users.

For information about the carriers and regions that are supported by intelligent DNS resolution, see Supported lines.

(2) Primary Address Pool Set

A primary address pool set is a collection of address pools that are accessed by users in normal conditions.

  • Address Pool Type: The available options include IPv4, IPv6, and Domain Name.

  • Select Address Pool: After you set the address pool type, select an existing address pool of the same type under the current instance or add an address pool of the specified type.

  • Load Balancing Policy: Set a load balancing policy for the address pools in the current address pool set. The available policies include Returns all addresses and Returns addresses by weight.

  • Min. Number of Available Addresses: Specify the minimum number of available addresses in the address pool set. If the number of available addresses in an address pool set is less than the minimum number of available addresses, the address pool set is unavailable.

(3) Secondary Address Pool Set

If the default address pool set is unavailable, GTM automatically switches to a secondary address pool set based on the switchover policy.

2. Access policy based on latency

(1) Primary Address Pool Set indicates a collection of address pools that are accessed by users in normal conditions.

a. Address Pool Type: Only IPv4 is supported.

b. Select Address Pool: After you set the address pool type, select an existing address pool of the same type under the current instance or add an address pool of the specified type.

c. Min. Number of Available Addresses: Specify the minimum number of available addresses in the address pool set. If the number of available addresses in an address pool set is less than the minimum number of available addresses, the address pool set is unavailable.

d. Max. Number of Addresses Returned:

    • The default value 1 indicates that if an application service has multiple IP addresses, GTM returns one IP address with the lowest access latency.

    • If this parameter is set to a value that is greater than 1 and less than 8, GTM returns multiple IP addresses with the lowest access latency.

e. Latency Resolution Scheduling Optimization:

    • If you enable this feature, GTM returns an optimal address from the addresses that are specified by the Max. Number of Addresses Returned parameter.

    • This feature can be enabled only if the Max. Number of Addresses Returned parameter is set to a value that is greater than 1.

(3) Secondary Address Pool Set

If the default address pool set is unavailable, GTM automatically switches to a secondary address pool set based on the switchover policy.

3. Switchover Policy of Effective Address Pool Set

The available switchover policies of address pool sets include Auto Switch and Manual Switching.

Mode

Condition

Primary address pool set

Secondary address pool set

Manual Switching

Specify a primary address pool set.

Specify a secondary address pool set.

Auto Switch

Specify a primary address pool set and do not specify a secondary address pool set.

Specify both primary and secondary address pool sets. The primary address pool set is available.

Specify both primary and secondary address pool sets. The primary address pool set is unavailable and the secondary address pool set is available.

Specify both primary and secondary address pool sets. Both the address pool sets are unavailable. The number of active addresses in the primary address pool set is more than that in the secondary address pool set.

Specify both primary and secondary address pool sets. Both the address pool sets are unavailable. The number of active addresses in the primary address pool set is less than that in the secondary address pool set.

Specify both primary and secondary address pool sets. Both the address pool sets are unavailable. The number of active addresses in the primary address pool set is the same as that in the secondary address pool set.

Description:

a. Auto Switch: After you add an access policy and save the settings, the Switchover Policy of Effective Address Pool Set parameter is automatically set to Auto Switch.

  • Auto Switch indicates automatic switchover between primary and secondary address pool sets based on the address pool set availability. If both the primary and secondary address pool sets are available, the primary address pool set is used.

  • If only the primary address pool set is configured, the primary address pool set is used.

  • If only the secondary address pool set is configured, the secondary address pool set is used.

  • If neither of the two address pool sets is available, the address pool set with a larger number of active addresses is used. If the numbers of active addresses in the address pool set are the same, the primary address pool set is used.

  • If neither of the two address pool sets is available and no active address exists, the primary address pool set is used.

  • The availability of an address pool set depends on the number of available IP addresses in the pool. If the number of available IP addresses is at least the value of the Min. Number of Available Addresses parameter, the address pool set is available. Otherwise, the address pool set is unavailable.

b. Manual Switching: You can manually set an active address pool set. Automatic switchover is not performed based on the availability of address pool sets.

Health check

After you turn on the Health Check switch, you can perform health checks for the IP addresses in an address pool to monitor the availability of applications in real time. This allows enterprises to achieve automatic fault isolation and switchover.

  • Available health check options: ping, tcp, and http(s).

  • Health check cycle: Each monitoring node independently runs health check tasks with an interval of 1 minute.

  • Monitoring nodes:

Category

Geographical location

Border Gateway Protocol (BGP) nodes

China (Zhangjiakou), China (Qingdao), China (Hangzhou), China (Shanghai), China (Hohhot), China (Shenzhen), and China (Beijing)

Nodes outside mainland China

China (Hong Kong), Germany (Frankfurt), Singapore (Singapore), US (California), Australia (Sydney), Malaysia (Kuala Lumpur), and Japan (Tokyo)

Carrier nodes

China Unicom in Wuhan, China Unicom in Dalian, China Unicom in Nanjing, China Unicom in Tianjin, China Telecom in Qingdao, China Telecom in Changsha, China Telecom in Xi'an, China Telecom in Zhengzhou, China Mobile in Shenzhen, China Mobile in Dalian, China Mobile in Nanjing

Failover

Failover is a core capability that is provided by GTM. The following features are supported:

a. GTM determines whether to return an IP address based on the health check result. If the IP address is available, DNS returns the IP address to clients. If the IP address is unavailable, GTM deletes the IP address.

Prerequisite: The Mode parameter of addresses is set to Smart Return.

b. You can configure a primary address pool set that is accessed by users in normal conditions and a secondary address pool set for redundancy. If the primary address pool set fails, the secondary address pool set is used to guarantee the stability of your business.

Prerequisite: The Switchover Policy of Effective Address Pool Set parameter is set to Auto Switch.

c. You can set the Min. Number of Available Addresses parameter for an address pool set. If the number of available IP addresses is less than the value of the Min. Number of Available Addresses parameter, GTM determines that the address pool set is unavailable and switches to the secondary address pool set.