After you enable the health check feature for an Edge Load Balancer (ELB) instance, ELB periodically checks whether the backend Edge Node Service (ENS) instances are healthy. If ELB detects an unhealthy ENS instance, ELB distributes new requests to other healthy ENS instances. After the unhealthy ENS instance recovers, ELB redistributes requests to the recovered ENS instance.
Why is a heath check required?
ELB performs health checks to check the availability of backend ENS instances. The health check feature improves overall service availability and reduces the impact of backend server failures.
If your business is highly sensitive to traffic fluctuations, frequent health checks may affect the availability of your business.
To reduce the adverse impacts of health checks on your business, you can reduce the health check frequency, increase the health check interval, or change Layer 7 health checks to Layer 4 health checks.
The health check feature is enabled by default. In most cases, you can use default health check configurations. You can also modify default configurations.
Procedure
Log on to the ENS console.
In the left-side navigation pane, choose .
On the ELB Instance page, find the ELB instance that you want to manage and click Listener Configuration in the Actions column.
On the Listener tab, click Add Listener or click Modify in the Actions column of an existing listener.
Configure the listener until you enter the Health Check step. Health check is enabled by default. Click Modify and configure the following parameters.
Parameter | Description |
Health Check Protocol | Select a protocol for health checks. For TCP listeners, TCP and HTTP health checks are supported.
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Health Check Method | Layer 7 listeners that use HTTP or HTTPS support the HEAD and GET methods. By default, the HEAD method is used. If your backend server does not support the HEAD method or the HEAD method is disabled, you can use the GET method. Note This feature is supported only if the listener protocol is set to HTTP or HTTPS. |
Health Check Path and Health Check Domain Name (Optional) | By default, when ELB performs HTTP health checks, ELB tests the default homepage that is configured on a backend Edge Node Service (ENS) instance by sending HTTP HEAD requests to the private IP address of the ENS instance. If you do not want to use the default homepage for health checks, you can specify a path. Note This feature is supported only if the listener protocol is set to HTTP or HTTPS. |
Normal Status Code | Select the HTTP status code that indicates successful health checks. Note This feature is supported only if the listener protocol is set to HTTP or HTTPS. |
Health Check Port | Specify the backend port that you want to probe. Note By default, the backend port that is specified in the listener configuration is probed. |
Response Timeout | Specify the timeout period for a health check response. If a backend server does not respond within the specified timeout period, the server fails the health check. Valid values: 1 to 300. Unit: seconds.
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Health Check Interval | Specify the interval between two consecutive health checks. Valid values: 1 to 50. Unit: seconds.
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Healthy Threshold | The number of times that an unhealthy backend server must consecutively pass health checks before the backend server is considered healthy.
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Unhealthy Threshold | The number of times that a healthy backend server must consecutively fail health checks before the backend server is considered unhealthy.
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