Configuring a Health Check

Scenarios

You can configure a health check when you add a listener. If you have no special requirements, retain the default settings.

Function Description

• The health check protocol can be different from the backend protocol.
• To reduce the CPU usage of backend servers, you can use TCP for health checks. If you want to use HTTP for health checks, use static files to obtain the health statuses.
• You can increase the health check interval to reduce the health check frequency.
• After you enable health checks, the load balancer immediately checks the health of backend servers and will start routing requests over new connections. If a backend server becomes unhealthy, the load balancer will stop routing traffic to it. However, request routing over established connections is not affected. To ensure service availability, you can enable health checks during off-peak hours.
• New requests are not routed to the backend server whose weight is 0, even if the backend server is considered healthy.

Configuring a Health Check for a Dedicated Load Balancer

1. Log in to the management console.
2. In the upper left corner of the page, click and select the desired region and project.
3. Hover on in the upper left corner to display Service List and choose Networking > Elastic Load Balance.
4. Locate the load balancer and click its name.
5. Click Backend Server Groups, locate the backend server group, and click its name.
6. In the Basic Information area, click Configure next to Health Check.
7. In the Configure Health Check dialog box, enable the health check. Configure the parameters based on Table 1.

   Table 1 Parameters for configuring a health check

   Parameter	Description	Example Value
   Enable Health Check	Specifies whether to enable health checks.	N/A
   Protocol	Specifies the protocol used by the load balancer to perform health checks on backend servers. You can select TCP, HTTP, or HTTPS. . If the frontend protocol is UDP, the health check protocol is UDP by default.	HTTP
   Domain Name	Specifies the domain name that will be used for health checks. This parameter is available when you set the health check protocol to HTTP or HTTPS. The domain name can contain digits, letters, hyphens (-), and periods (.), and must start with a digit or letter. The field is left blank by default and must start with a digit or letter.	www.elb.com
   Port	Specifies the port used by the load balancer to perform health checks on backend servers. The port number ranges from 1 to 65535. NOTE: This parameter is optional. If you do not specify a health check port, a port of the backend server will be used for health checks by default. If you specify a port, it will be used for health checks.	80
   Check Path	Specifies the health check URL, which is the destination on backend servers for health checks. Configure this parameter only if you have set Protocol to HTTP. The value can contain 1 to 80 characters and must start with a slash (/). The value can contain letters, digits, hyphens (-), slashes (/), periods (.), percent signs (%), ampersands (&), and the following special characters: _~';@$*+,=!:()	/index.html
   Interval (s)	Specifies the maximum time between two consecutive health checks, in seconds. The interval ranges from 1 to 50.	5
   Timeout (s)	Specifies the maximum time required for waiting for a response from the health check, in seconds. The timeout duration ranges from 1 to 50.	3
   Maximum Retries	Specifies the maximum number of health check retries. The value ranges from 1 to 10.	3

8. Click FinishOK.

Follow-Up Operations

• How Do I Troubleshoot an Unhealthy Backend Server?
• Why Does ELB Frequently Send Detection Requests to Backend Servers During Health Checks?