Alibaba Cloud DNS:Ping health check

What is a ping health check

A ping health check is a method that Global Traffic Manager (GTM) uses to monitor the health of IP addresses in an address pool. GTM probes each IP address to check the status of the application service that runs on it. If an IP address becomes unhealthy, GTM automatically removes it from DNS responses. When the IP address becomes healthy again, GTM automatically resumes including it in DNS responses.

Parameters

1. Health check protocol

   This topic describes the Ping protocol, which monitors metrics such as network reachability, packet loss rate, and latency for a target IP address.

2. Health check interval

   The interval between health check probes for each IP address. The default interval is 1 minute. The minimum interval is 15 seconds, which is available only to users of the Ultimate Edition.

3. Ping packets

   The number of ping packets sent in each health check probe. This value is used to calculate the packet loss rate. The value is fixed at 20.

4. Packet loss rate

   If the packet loss rate of an IP address reaches this threshold, the address is considered unhealthy. The rate is calculated as (Lost packets / Total packets sent) * 100%. Available thresholds: 10%, 30%, 50%, 80%, 90%, and 100%.

5. Timeout

   The maximum time to wait for a ping response. If a response is not received within this period, the packet is considered lost. Available values: 2s, 3s, 5s, and 10s.

6. Consecutive failures

   The number of consecutive failed probes required to mark an application service as unhealthy. This setting helps prevent incorrect health statuses caused by transient network jitter. Available values: 1, 2, and 3.

• 1: The application service becomes unhealthy after one failed health check.

• 2: The application service becomes unhealthy after two consecutive failed health checks.

• 3: The application service becomes unhealthy after three consecutive failed health checks.

  Important

  Conditions such as total network unreachability or ICMP destination unreachable responses are not counted as packet loss. Therefore, they do not trigger the unhealthy state based on the packet loss rate threshold. To resolve this, ensure the network path is valid or switch to an HTTP health check.

7. Failure rate

   If the percentage of monitoring nodes reporting a failure exceeds this threshold, the application service is marked as unhealthy. Available thresholds: 20%, 50%, 80%, and 100%.

8. Monitoring nodes

   The locations from which GTM sends health check probes. GTM provides the following default monitoring nodes:

   Important

   If your address pool contains only Alibaba Cloud IP addresses and you use blackhole filtering for fault testing, you must select ISP nodes for monitoring. This is because blackhole filtering is an access control list (ACL) policy that takes effect at the internet boundary between the cloud network and carrier networks. Traffic between Alibaba Cloud IP addresses typically remains within the internal cloud network, bypassing this boundary and rendering the probes ineffective.

   Node type	Geographic locations
   BGP node	Zhangjiakou, Qingdao, Hangzhou, Shanghai, Hohhot, Shenzhen, Beijing
   Overseas node	China (Hong Kong), Germany, Singapore, California, Malaysia, Japan
   ISP node	China Unicom (Wuhan, Dalian, Nanjing, Tianjin), China Telecom (Qingdao, Changsha, Xi'an, Zhengzhou), China Mobile (Shenzhen, Dalian, Nanjing)

Procedure

1. Log in to the Alibaba Cloud DNS - Global Traffic Manager console.

2. On the instance list page, find the target instance and click Actions in the Configure column.

• If you have not configured GTM for the instance, follow the instructions in enable health checks.

• If you have already configured GTM for the instance, click the Address Pools tab. Click the + icon next to the address pool that you want to manage. In the Health Check section, click Modify to configure settings such as health check interval, timeout, consecutive failures, and monitoring nodes.