A TCP health check is a network protocol that Global Traffic Manager (GTM) uses to check the health of target addresses. This health check monitors metrics such as network reachability, port availability, and the latency of IP addresses. If an IP address or port becomes abnormal, GTM automatically blocks the abnormal IP address. When the IP address returns to normal, GTM automatically unblocks it.
Configuration parameters
Template Name: The name of the health check template. For easy identification, use a name that indicates the health check protocol.
Type: The IP address type of the probe nodes. Valid values are IPv4 and IPv6.
Protocol
The health check uses the TCP protocol to check the target IP address. It monitors metrics such as network reachability, port availability, and latency.
Interval
The interval at which TCP health checks are performed. The default value is 1 minute. The minimum interval is 15 seconds. This feature is available only for the Ultimate Edition.
Timeout Period
The period to wait for a response to a TCP packet. If a response is not received within the specified timeout period, the health check fails. You can set the timeout to 2, 3, 5, or 10 seconds.
Retries
The number of consecutive times a health check must fail before the application service is marked as abnormal. This feature helps prevent temporary issues, such as network jitter, from affecting monitoring accuracy. You can set the number of consecutive failures to 1, 2, or 3.
1: If one health check fails, the application service is marked as abnormal.
2: If two consecutive health checks fail, the application service is marked as abnormal.
3: If three consecutive health checks fail, the application service is marked as abnormal.
Detection Node
The geographic locations of the nodes that perform TCP health checks. The following default detection nodes are provided:
Node type
Geographic location
BGP node
Qingdao, Zhangjiakou, Beijing, Hohhot, Shenzhen, Shanghai, Hangzhou
International node
Malaysia, Germany, China (Hong Kong), Singapore, California, Japan
Carrier node
Changsha Telecom, Xi'an Telecom, Nanjing Unicom, Zhengzhou Telecom, Tianjin Unicom, Nanjing Mobile, Dalian Unicom, Shenzhen Mobile, Dalian Mobile, Qingdao Telecom
ImportantIf all addresses in the address pool are Alibaba Cloud addresses and you use a blackhole filtering policy for fault testing, select carrier nodes as the probe nodes. This is because blackhole filtering is an access control list (ACL) policy that takes effect on the Internet traffic between the Alibaba Cloud network and carrier networks. Traffic between Alibaba Cloud IP addresses flows mostly within the Alibaba Cloud network, which reduces the effectiveness of the probes.
Difference between BGP nodes and carrier nodes: Border Gateway Protocol (BGP) nodes automatically select the optimal carrier network. For example, if you use a BGP node in Shanghai and the China Mobile line fails, the probe node may switch to the China Telecom line. The probe node switches to an available line unless all lines fail. In contrast, a carrier node uses only its specified carrier network and does not have this optimization mechanism.
To configure a whitelist for access sources on your server, click View Monitoring Node IP Addresses to obtain the IP addresses of the probe nodes.
If the IP address to be probed is located outside China, select international nodes.
Detected Node Failure Rate
The application service is marked as abnormal if the percentage of selected detection nodes that report a health check failure exceeds this threshold. You can set the failure rate threshold to 20%, 50%, 80%, or 100%.
Configuration methods
Create a detection template
On the Health Check Template tab, click Create Health Check Template. In the dialog box that appears, configure the parameters and submit the form.
Modify a probe template
Go to the Alibaba Cloud DNS - Global Traffic Manager console.
On the Health Check Template tab, find the probe template that you want to modify and click the Configure button.
In the dialog box that appears, modify the parameters and submit the changes.
ImportantThe Type cannot be modified.
Delete a probe template
Go to the Alibaba Cloud DNS - Global Traffic Manager console.
On the Health Check Template tab, find the target probe template and click Delete in the Actions column.
In the dialog box that appears, confirm the deletion.
WarningA template cannot be recovered after it is deleted. The health check tasks associated with the template are also deleted. As a result, the health status of the associated addresses can no longer be probed. Before you proceed, confirm that you want to delete the template.