An address pool is a group of IP addresses or domain names that provide the same application service. All addresses in a pool share the same carrier or regional properties.
Purpose of address pools
Address pools are a feature of Global Traffic Manager (GTM) for managing application service addresses. You can configure multiple address pools for a GTM instance. This lets you route users from different regions to different address pools for proximity-based routing. It also enables failover if an entire address pool collection becomes unavailable.
Add an address pool
Click the Address Pool Configuration tab, and then click the Create Address Pool button.
On the Create Address Pool page, click the address pool icon and select Basic Configuration.
In the Address Pool Basic Configuration dialog box, configure the parameters and click Submit Configuration.
Item
Description
Address Pool Name
Enter an easy-to-remember name for the address pool, such as "test". Access policies use this name to identify the address pool.
Address Pool Type
Options: IPv4, IPv6, and Domain Name.
NoteThe address pool type is associated with the Record Type selected for the access domain name. The relationships are as follows:
If the GTM access domain name has a record type of A, the address pool can be of type IPv4 or Domain Name.
If the GTM access domain name has a record type of AAAA, the address pool can be of type IPv6 or Domain Name.
If the GTM access domain name has a record type of CNAME, the address pool can only be of type Domain Name.
Address Pool Health Status Condition
This metric determines if the address pool is available. The address pool is considered unavailable if the number of available addresses in it falls below this value. The options are:
At least 1 address in the address pool is available
At least 30% of addresses in the address pool are available
At least 50% of addresses in the address pool are available
At least 70% of addresses in the address pool are available
All addresses in the address pool are available
Enabled Status
Enabled by default. If set to Disabled, GTM does not return addresses from this address pool.
Remarks
Enter a description for the address pool. This helps you identify it later.
Add addresses to an address pool
After you configure the basic settings for the address pool, on the Address Pool page, click the address pool icon and select the Select Existing Address button.
NoteIf you have not configured any addresses, click Add New Address to configure one. For more information, see Address configuration.
After you add the service addresses, click the Submit Configuration button.
Add an address pool to an access domain name
After you configure an address pool, add it to a target access domain name.
Go to Alibaba Cloud DNS - Global Traffic Manager, find the target domain name, and click Configuration in the Actions column to open the configuration page.
Click the Access Domain Name icon, and in the dialog box that appears, click Select Existing Address Pool.
In the Select Existing Address Pool panel that appears, select the address pool that you configured.
Configure a load balancing policy for address pools
GTM provides four load balancing policies for address pools: Round-robin, Sequential, Weighted, and Source Proximity. Select the policy that best suits your business scenario.
Policy descriptions
Round-robin
For each DNS query, all available address pools are returned. The order of the address pools is rotated for each query. The client typically accesses an address from the first address pool in the list.
1st query: Address Pool 1, Address Pool 2, Address Pool 3
2nd query: Address Pool 3, Address Pool 1, Address Pool 2
3rd query: Address Pool 2, Address Pool 3, Address Pool 1
4th query: Address Pool 1, Address Pool 2, Address Pool 3
Limits: You cannot configure a round-robin policy if two address pools are of different types or if both are of the domain name type. For example, you cannot use a round-robin policy for an IPv4 address pool and a domain name address pool, an IPv6 address pool and a domain name address pool, or two domain name address pools.
Scenarios
Load balancing traffic between multiple peer data centers (active-active architecture).
Simple traffic distribution scenarios that do not require high precision.
Recommendations: Because of DNS caching and client behavior, the actual traffic distribution may not be a strict 1:1:1 round-robin. However, the traffic tends to balance out over time.
Sequential
For each DNS query, GTM returns the available address pool with the smallest ordinal number. The ordinal number indicates the priority of the address pool. A smaller number indicates a higher priority. If the highest-priority address pool is unavailable, the address pool with the next smallest ordinal number is returned. In sequential mode, there are two service recovery modes that apply when a higher-priority resource becomes available again: Preemptive Mode and Non-preemptive Mode.
Preemptive Mode: Prioritizes the resource with the smaller ordinal number when a resource recovers.
For example, Address Pool 1 has ordinal number 1, Address Pool 2 has 2, and Address Pool 3 has 3. If Address Pool 1 is available, it is always returned.
If Address Pool 1 is abnormal, Address Pool 2 is returned. If both Address Pool 1 and Address Pool 2 are abnormal, Address Pool 3 is returned. If both Address Pool 1 and Address Pool 2 recover, Address Pool 1 is returned.
Non-preemptive Mode: When a higher-priority resource recovers, the current resource continues to be used.
For example, Address Pool 1 has ordinal number 1, Address Pool 2 has 2, and Address Pool 3 has 3. If Address Pool 1 is available, it is always returned.
If Address Pool 1 is abnormal, Address Pool 2 is returned. If both Address Pool 1 and Address Pool 2 are abnormal, Address Pool 3 is returned. If both Address Pool 1 and Address Pool 2 recover, Address Pool 3 is still returned.
Scenarios
Scenario | Recommended Mode | Reason |
Active-standby disaster recovery | Non-preemptive Mode | This avoids the risk of data loss caused by data inconsistency between the active and standby data centers. After traffic switches to the standby center and new data is generated, if the active center recovers and immediately preempts traffic, the new data from the standby center may not have been synced back. This can cause access errors or data loss for users. |
Performance tiers | Preemptive Mode | Prioritize using high-performance or low-latency resource pools to ensure a good user experience. When the high-performance resource recovers, traffic should switch back immediately. |
Cost optimization | Preemptive Mode | Prioritize using low-cost resource pools, such as subscription resources. Switch to high-cost pay-as-you-go resources only during a failure. Switch back immediately after the primary resource recovers to save costs. |
Weight
You can set an integer weight value from 1 to 100 for each address pool. GTM distributes DNS queries based on the specified weight ratio. The higher the weight, the greater the probability that the address pool is returned.
Scenarios
Phased release: Direct a small amount of traffic, such as 5%, to a newly deployed address pool to verify its stability.
Proportional traffic switching: Distribute traffic proportionally based on the processing capacity of different data centers.
Recommendations
Weight drift: Because of the effects of DNS caching at various levels, the actual service traffic ratio may differ from the configured weights. This behavior is expected. Calibrate the weights based on your business monitoring data instead of relying solely on DNS query statistics.
Weight precision: To make weight adjustments more effective, the difference between weight values should be at least 10.
Source Proximity
GTM uses the source IP address of the DNS query to match an available address pool. It prioritizes matches based on the granularity of the source line. If a source matches multiple available address pools, GTM returns the one with the smallest ordinal number.
Scenarios
You have data centers deployed in multiple locations globally or nationally and want to provide the best access experience for users in different regions.
Recommendations
You must configure a default line to match all unspecified source regions. This ensures global service availability.
Procedure
Go to Alibaba Cloud DNS - Global Traffic Manager, find the target access domain name, and open its configuration details page.
Click the load balancing policy between address pools under the access domain name, such as Round-robin. The configuration panel appears.
Click Configure Load Balancing Policy and select Load Balancing Policy (between address pools).
Except for the Round-robin policy, other policies require you to configure policy data for each address pool. For example:
Sequential: Set an ordinal number for each address pool (a smaller number indicates a higher priority), and select Preemptive Mode or Non-preemptive Mode based on the recommendations above.
Weighted: Set an integer weight value from 1 to 100 for each address pool.
Source Proximity: For each planned access source, such as a region, country, province, or carrier, select the corresponding address pool. You must also configure a default address pool.
Verification: You can verify that the policy has taken effect by checking the DNS records. You can also detect address changes by querying public DNS servers.
dig @223.5.5.5 your-domain.com +short dig @8.8.8.8 your-domain.com +short
Address pool status changes
Service Availability Status: Indicates the service availability of an address pool. The status can be Available or Unavailable.
Available: If an address pool is Enabled and its health status is Normal, its service availability status is Available.
Unavailable: If an address pool is Disabled or its health status is Abnormal, its service availability status is Unavailable.
The following table shows the priority used to determine the service availability status of an address pool:
Enabled Status | Health Status | Service Availability Status |
Enabled | Normal or Warning | Available |
Enabled | Abnormal | Unavailable |
Disabled | Normal, Warning, or Abnormal | Unavailable |
Address pool health status:
Normal: All referenced addresses in the address pool are available. The health status of the address pool is Normal.
Warning: Some referenced addresses in the address pool are unavailable. However, the number of unavailable addresses does not exceed the configured health status condition. The health status of the address pool is Warning. In the Warning state, DNS queries resolve to the available addresses in the pool, but not to the unavailable addresses.
Abnormal: The number of unavailable referenced addresses in the pool exceeds the configured health status condition. The health status of the address pool is Abnormal. An abnormal address pool stops responding to DNS queries.