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Last Updated: Oct 11, 2021

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

GTM uses DNS to translate a domain name into multiple IP addresses. Therefore, different visitors 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 translated by DNS. This allows the system to implement fault isolation and failover. As a result, visitors can directly connect to the related IP addresses to access an application service. In this case, visitors 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

Layer

Backend address

Weighted round robin

Cross-region difficulty

Fault isolation time

Session persistence

GTM

3

Domain names and IP addresses

Supported

Easy

Minute-level

Not supported

SLB

4 and 7

IP

Supported

Difficult

Second-level

Supported

What are the differences between GTM, Alibaba Cloud DNS, and global server load balancing (GSLB)?

GTM functions based on Alibaba Cloud DNS and Cloud Monitor. GTM integrates the intelligent DNS resolution feature and the application service monitoring feature of Cloud Monitor. GTM also provides several different features. These features include nearby access for visitors from different regions or areas, health checks that you can perform to monitor the statuses of application services, and automatic failover. GTM is used to improve and replace the GSLB feature of Alibaba Cloud DNS. Compared with GSLB, GTM provides more monitoring methods, more advanced IP management features, and more reliable and timely monitoring results.

If you are using the GSLB feature of Alibaba Cloud DNS, we recommend that you migrate the resources that are managed by this feature to GTM. The network monitoring and GSLB features of Alibaba Cloud DNS are phased out. You will receive a notification at least one month before these features are disabled.

The following table describes the differences.

Item

Service access

Health check

Billing

Cross-account

Failover time

Multi-line access

Active-standby policy

GTM

CNAME access

Ping, TCP, HTTP, and HTTPS.

By instance.

No limit.

Minute-level. The time is not subject to the TTL of subdomains.

China Unicom, China Telecom, China Mobile, Dr. Peng.

Automatic failover. Controllable.

GSLB

Subdomains are enabled.

Not supported. This feature must integrate with the network monitoring feature.

Extra payment for a monitoring service is required.

This feature is available only for domain accounts.

This time is subject to the TTL of subdomains.

Not supported. This feature must integrate the required line settings in Alibaba Cloud DNS.

No predefined rules except that a backup line is randomly selected and must be normal. Uncontrollable.

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

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

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

GTM integrates the application service monitoring feature. GTM 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 over ping, TCP, or HTTP.

  • 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?

A: GTM requires about 1 minute to complete a failover after an application service fails. The Alibaba Cloud test team performs multiple tests to verify this test result. Failover time of GTM = Failure detection time + Network-wide switchover time

Note

The network-wide switchover time is subject to multiple factors. These factors include the specified dialing test platform, detection points, TTL cache of each domestic carrier, and testing time.

Notice

The Standard Edition requires about 3 minutes to complete a failover after a failure is identified.

  • Failure detection time: The time remains unchanged. By default, after the health check feature is enabled, GTM requires about 3 minutes to complete a failover after a failure occurs.

  • Network-wide switchover time: The time varies based on the TTL cache settings of each domestic carrier and network environment. Therefore, the time is subject to the specified cache time of each domestic carrier.

The Ultimate Edition requires about 1 minute to complete a failover after a failure is identified.

  • Failure detection time: You can set the health check interval to 15 seconds, TTL to 10 seconds, and number of consecutive failures to 3. In this case, GTM requires about 1 minute to identify a failure after the failure occurs.

  • Network-wide switchover time: The time varies based on the TTL cache settings of each domestic carrier and network environment. Therefore, the time is subject to the specified cache time of each domestic carrier.

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 at the same time. When 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 intelligent DNS resolution. This feature allows GTM to translate addresses from the four major carriers of China, seven regions, and six continents outside mainland China. This feature also allows visitors 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 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?

A: Yes, you can. You can deploy Alibaba Cloud CDN in front of GTM. For more information, see Implement regional intelligent resolution by using GTM.

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

A: Yes, you can add a CNAME access domain name 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 is limited. GTM cannot obtain the accurate statuses of health checks or implement failover. Therefore, we recommend that you do not use this method to add an address to an address pool.