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Global Traffic Manager:FAQ

Last Updated:Mar 15, 2024

Why does the geographical location-based access policy of a Global Traffic Manager (GTM) instance not take effect?

The line type configured for the custom canonical name (CNAME) of the GTM instance conflicts with the line type configured for the access policy of the GTM instance. For more information, see Troubleshoot ineffective DNS records for regional lines for a GTM instance.

What are the differences between GTM and Server Load Balancer (SLB)?

GTM uses Domain Name System (DNS) to resolve a domain name to multiple IP addresses. Therefore, different users can access different IP addresses. This allows GTM to balance the access traffic of an application service across multiple IP addresses. GTM uses health checks to dynamically update the IP addresses that are resolved by DNS. This allows the system to implement fault isolation and failover. As a result, users can directly connect to the related IP addresses to access an application service. In this case, users do not need to connect to GTM. SLB serves as a proxy to which user requests are sent. Then, SLB distributes these user requests across different instances. As a result, all access traffic must be first converged on SLB.

In most cases, you can use SLB to balance workloads across multiple IP addresses that reside in the same region. If you need to balance workloads across multiple SLB addresses that reside in different regions, use GTM.

The following table describes the differences.

Item

Network layer

Backend address

Weighted round-robin

Cross-region load balancing difficulty

Fault isolation time

Session persistence

GTM

3

Domain names and IP addresses

Supported

Easy

Within minutes

Not supported

SLB

4 and 7

IP

Supported

Difficult

Within seconds

Supported

What are the differences between GTM and Alibaba Cloud DNS?

GTM functions based on Alibaba Cloud DNS and CloudMonitor. GTM integrates with the intelligent DNS resolution feature and the application service monitoring feature of CloudMonitor. GTM also provides several different features. These features include nearby access for users from different networks or regions, health checks that you can perform to monitor the statuses of application services, and automatic failover.

Can I use a URL to access the CNAME of a GTM instance?

No, you cannot use the CNAME of the GTM instance as a URL that is accessed by users. The CNAME of GTM functions in the same way as the CNAME of Alibaba Cloud services, for example, Alibaba Cloud CDN. A CNAME can only point to an application service. You cannot use a CNAME as a URL that can be accessed by users.

How can I use GTM to check whether an application service fails?

GTM integrates with the application service monitoring feature and provides 14 monitoring nodes around the world. You can specify a group of monitoring nodes for an application service and check whether the application service fails based on the alert logs that are received from these monitoring nodes. To check whether an application service fails, you can monitor the application service by using ping-based health checks, TCP health checks, and HTTP or HTTPS health checks.

  • Ping-based health check: checks whether an application service fails based on the packet loss rate or response time.

  • TCP health checks: checks whether an application service fails based on the response time of a TCP port.

  • HTTP or HTTPS health checks: checks whether an application service fails based on the HTTP or HTTPS response time or return code.

How long is the failover period of GTM?

According to the test results of the Alibaba Cloud test team, GTM takes about 1 minute to complete a failover after an application service fails. Network-wide recovery time = Failure detection time + Network-wide failover time.

Note

The network-wide failover time is subject to multiple factors. These factors include the specified dialing test platform, detection points, TTL of cache for different Internet service providers (ISPs), and testing time.

Important

Standard Edition takes about 4 minutes to complete a failover after a failure is detected.

  • Failure detection time: The time is ensured. By default, after the health check feature is enabled, GTM takes about 4 minutes to complete a failover after a failure occurs.

  • Network-wide failover time: The time varies based on the TTL settings of ISPs and the network environment. Therefore, the time is subject to the specified TTL value of each ISP.

Ultimate Edition takes about 1 minute to complete a failover after a failure is detected.

  • Failure detection time: You can set the health check interval to 15 seconds, TTL to 1 second, and the number of consecutive failures to 3. In this case, GTM takes about 1 minute to detect a failure after the failure occurs.

  • Network-wide failover time: The time varies based on the TTL settings of ISPs and the network environment. Therefore, the time is subject to the specified TTL value of each ISP.

Can I specify domain names in a GTM address pool?

Yes, you can specify domain names in a GTM address pool. GTM allows you to specify IP addresses or domain names in an address pool. However, an address pool cannot contain both IP addresses and domain names. If an address pool has multiple domain names, GTM balances workloads across these domain names based on the round-robin results.

Can I use GTM to implement intelligent DNS access?

Yes, you can use GTM to implement intelligent DNS access. GTM integrates with intelligent DNS resolution. This feature allows GTM to resolve addresses from the four major ISPs of China, seven regions, and six continents outside the Chinese mainland. This feature also allows users from different networks or regions to access the nearest nodes. This way, network access is accelerated.

Does GTM support the session persistence feature?

No, GTM does not support the session persistence feature. GTM is a DNS-level management system. GTM routes clients to the related addresses of an application service based on DNS responses. To access an application service, clients can directly connect to the related IP addresses. In this case, clients do not need to connect to GTM. You cannot view the HTTP traffic between clients and GTM. Therefore, GTM does not support the session persistence feature.

Can I add a domain name to GTM and Alibaba Cloud CDN at the same time?

Yes, you can add a domain name to GTM and Alibaba Cloud CDN at the same time. You can deploy Alibaba Cloud CDN in front of GTM. For more information, see Implement switchover for origin IP addresses by using GTM.

Can I add a CNAME of a CDN service provider to an address pool of GTM?

Yes, you can add a CNAME of a CDN service provider to an address pool of GTM. However, this setting cannot allow the health check and failover features to achieve an optimal result. In most cases, a CDN service provider has a large number of CDN nodes. Compared with the number of CDN nodes, the number of monitoring nodes of GTM is limited. GTM cannot obtain the accurate statuses of health checks and implement failover. Therefore, we recommend that you do not perform this operation.