Alibaba Cloud DNS:Features

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

Basic settings

After you create a GTM instance, you can configure the basic settings and enable an access policy type for the instance. You can configure basic parameters including Instance Name, CNAME Access Type, Business Domain Name, Global TTL, Alert Group, and Notification Methods. You can enable geographical location-based or latency-based access policies for the instance.

1. Access policy types

(1) Geographical Location-based Access Policy

These policies allow users from different regions or networks to access the nearest node and accelerate access based on the geographical locations of users.

(2) Latency-based Access Policy

These policies allow GTM to detect the access latency between the location of a user and the region in which an application service is deployed. Then, GTM routes the requests from the user to the application server cluster that has the lowest latency. This policy type is available only in GTM instances of Ultimate Edition.

2. Basic settings

(1) CNAME(Internet)

GTM provides the traffic scheduling service by using CNAME records. You must create a CNAME record to map your business domain name to the access domain name of your GTM instance in the Alibaba Cloud DNS console. You can use a public domain name within your account as the suffix of a custom access domain name. The public domain name must be hosted by Alibaba Cloud DNS.

(2) Load Balancing Policy(Address Pool)

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 the specified weights. This way, access traffic is distributed based on address weights.

(3) Global TTL Period

A global time to live (TTL) period 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 custom access 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) Business Domain Name(Internet)

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

(5) Alert Group

An alert contact group is used to receive notifications if errors occur. You can configure an alert contact group in CloudMonitor. 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) Notification Methods

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

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 Type

• Geographical location-based access policies support address pools that contain IPv4 addresses, IPv6 addresses, or domain names.

• Latency-based access policies support address pools that contain IPv4 addresses.

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 Rectify to modify the geographical location of the application service.

3. Mode

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

• Intelligently Returned: This mode is used by default. GTM determines whether to return an address based on the health check result. If the address is available, DNS returns the address to clients. If the address is unavailable, GTM suspends the 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 must first set the Mode parameter of the address to Always Offline.

4. 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 specified weights. This way, access traffic is distributed based on address weights. You can set load balancing policies for address pools and addresses.

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 8, which is obtained by multiplying 4 and 2.

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 9, which is obtained by adding the product of 4 and 2 to the product of 1 and 1.

Access policies

1. Geographical location-based access policies

(1) DNS Request Source

You can specify DNS request sources to achieve intelligent DNS resolution. After you specify a region for an access policy, access to an application service from this region is routed to the specified address pool set. A value of Global indicates that the access policy applies to all users.

For information about the carriers and regions that are supported by intelligent DNS resolution, see the "Supported intelligent resolution lines" section of the Intelligent DNS resolution topic.

(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: Valid values are IPv4, IPv6, and Domain Name.

• Address Pool: After you set the address pool type, select one or more existing address pools of the specified type or create address pools of the specified type.

• Load Balancing Policy(Address Pool): Select a load balancing policy for the address pools in the address pool set. Valid values: Return All Addresses and Return Addresses by Weight.

• Minimum 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 the secondary address pool set based on the switchover policy.

2. Latency-based access policies

(1) 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: Only IPv4 is supported.

• Address Pool: After you set the address pool type, select one or more existing address pools of the specified type or create address pools of the specified type.

• Minimum 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.

• Maximum 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.

• DNS Resolution with Optimal Latency:

  • If you enable this feature, GTM intelligently returns the addresses with optimal latency. The number of returned addresses is less than the value of the Maximum Addresses Returned parameter.

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

(2) Secondary Address Pool Set

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

3. Switchover policy of address pool sets

Valid values of the Address Pool Set Switchover Policy parameter: Automatic Switchover and Manual Switchover.

Description:

(1) Automatic switchover: After you create an access policy, automatic switchover is used by default.

• In this mode, GTM switches between the primary address pool set and the secondary address pool set based on their availability. The primary address pool set is used when both the primary and secondary address pool sets are available.

• 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 available addresses is used. If the numbers of available 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 available 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 Minimum Available Addresses parameter, the address pool set is available. Otherwise, the address pool set is unavailable.

(2) Manual switchover: You can manually set an available address pool set. Automatic switchover is not performed based on the availability of address pool sets.

Health checks

After you configure health checks for an address pool, you can perform health checks for the IP addresses in the 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-based health checks, TCP-based health checks, and HTTP or HTTPS health checks.

• Health check cycle: Each monitoring node independently runs health check tasks at intervals of 1 minute.

• Monitoring nodes

Failover

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

1. 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 suspends the IP address.

Prerequisite: The Mode parameter of addresses is set to Intelligently Returned.

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

Prerequisite: The Address Pool Set Switchover Policy parameter is set to Automatic Switchover.

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