Alibaba Cloud DNS:TCP health checks

Overview

TCP is one of the network protocols over which Global Traffic Manager (GTM) performs health checks on IP addresses. TCP health checks are performed to monitor multiple metrics of IP addresses. These metrics include network accessibility, port availability, and latency. When a monitored IP address or the port of a monitored IP address is abnormal, the system blocks the IP address. When the IP address or the port becomes normal, the system unblocks the IP address.

Configuration parameters

1. Template Name: This parameter specifies the name of the health check template. We recommend that you use network protocols for health checks to name templates for easy identification.

2. Detection Type: This parameter specifies the IP address type of health check nodes. Valid values: IPv4 and IPv6.

3. Detection Protocol

   This parameter specifies the protocol that is used to monitor the metrics of IP addresses. These metrics include network accessibility, port availability, and latency. In this example, tcp is selected.

4. Health Check Interval

   This parameter specifies the interval between TCP health checks. Default value: 1 Minute. GTM Ultimate Edition supports a minimum interval of 15 seconds.

5. Timeout Period

   This parameter specifies the timeout period of a health check. During a TCP health check, the system calculates the response time of each TCP packet that is sent. If the response time of a packet exceeds the specified timeout period, the health check times out. Valid values: 2 Seconds, 3 Seconds, 5 Seconds, and 10 Seconds.

6. Retries

   This parameter specifies the maximum number of consecutive health checks that an address of an application service fails before the address is deemed abnormal. During TCP health checks, an application service is deemed abnormal only if consecutive health checks determine that an address of the application service is abnormal. The setting of this parameter prevents the accuracy of health checks from being affected by issues such as instantaneous network jitters. Valid values: 1, 2, and 3.

   • The value 1 indicates that an address of an application service is deemed abnormal when one health check determines that this address is abnormal. In this case, one alert is reported.

   • The value 2 indicates that an address of an application service is deemed abnormal when two consecutive health checks determine that this address is abnormal. In this case, two alerts are reported.

   • The value 3 indicates that an address of an application service is deemed abnormal when three consecutive health checks determine that this address is abnormal. In this case, three alerts are reported.

6. Detection Node

   This parameter specifies the geographical locations of nodes that perform TCP health checks. The following table lists the health check nodes that are provided by default.

   Node type	Node name
   BGP Nodes	Zhangjiakou, Qingdao, Hangzhou, Shanghai, Huhehaote, Shenzhen, and Beijing
   Overseas Nodes	Hong Kong, Germany, Singapore, Silicon Valley, Malaysia, and Japan
   ISP Nodes	DalianChina-Unicom, NanjingChina-Unicom, TianjinChina-Unicom, QingdaoChina-Telecom, ChangshaChina-Telecom, XianChina-Telecom, ZhengzhouChina-Telecom, ShenzhenChina-Mobile, DalianChina-Mobile, and NanjingChina-Mobile

   Important

   • If all addresses in an address pool are Alibaba Cloud IP addresses and the blackhole filtering policy is used for fault detection, select Internet service provider (ISP) nodes as detection nodes. Reason: Blackhole filtering is an access control list (ACL) policy that takes effect on the Internet between the Alibaba Cloud network and ISP networks. Traffic between Alibaba Cloud IP addresses flows in the cloud network. This reduces the detection accuracy.

   • Differences between Border Gateway Protocol (BGP) nodes and ISP nodes: BGP nodes select optimal ISP lines. For example, if BGP nodes in Shanghai are used, the China Telecom lines in Shanghai may be used when the China Mobile lines in Shanghai fail. If all lines fail, BGP nodes stop performing health checks. However, if ISP nodes are used, only networks provided by the corresponding ISP are used.

   • If you need to configure a whitelist policy for access sources on a server, you can click View Monitoring Node IP Addresses to obtain the IP addresses of the detection nodes.

   • If the IP address to be checked is outside the Chinese mainland, select nodes outside the Chinese mainland.

7. Detected Node Failure Rate

This parameter specifies the ratio of health check nodes that detect exceptions to all health check nodes during TCP health checks. If the actual ratio is greater than or equal to the specified value, an address of an application service is deemed abnormal. Valid values: 20%, 50%, 80%, and 100%.

Procedure

Create a health check template

1. Log on to the Alibaba Cloud DNS console.

2. In the left-side navigation pane, click Global Traffic Manager. On the page that appears, click the Global Traffic Manager3.0 tab.

3. Click the Health Detection Template tab. Then, click Create Detection Template. In the panel that appears, configure the parameters and click OK.

   Note

   If you want to create more health check templates, click Add and Continue.

   

Modify a health check template

1. Log on to the Alibaba Cloud DNS console.

2. In the left-side navigation pane, click Global Traffic Manager. On the page that appears, click the Global Traffic Manager3.0 tab.

3. On the Global Traffic Manager 3.0 page, click the Health Detection Template tab, find the health check template that you want to modify, and then click Configuration in the Actions column.

4. In the panel that appears, modify the parameters and click OK.

   Important

   The Detection Type parameter cannot be modified.

Delete a health check template

1. Log on to the Alibaba Cloud DNS console.

2. In the left-side navigation pane, click Global Traffic Manager. On the page that appears, click the Global Traffic Manager3.0 tab.

3. On the Global Traffic Manager 3.0 page, click the Health Detection Template tab, find the health check template that you want to delete, and then click Delete in the Actions column.

4. In the Confirm Deletion message, check the IP addresses that are associated with the template and click OK.

   Warning

   Note the following impacts after a health check template is deleted: The template cannot be restored. Health check tasks that are performed on the addresses in the template are deleted as well. The health status of the associated addresses cannot be checked. Please exercise caution before you proceed with this operation.