<p>The ELB service will check the health status of the hosts in the server resource pool. If the ELB service finds that there is a problem with a host, it will forward the request to other normal hosts. When the host returns to normal, the ELB service will resend the request to the host. ELB will test the running status of the back-end server by periodically sending requests to them. Currently, Ping An Cloud provides two health checks, TCP and HTTP.</p> <p><strong><span style="font-size:18px">TCP Health Check</span></strong></p> <p>The four-layer health check uses TCP detection to obtain status information. It is necessary to open the corresponding server back-end port when creating the resource pool.</p> <p><strong><span style="font-size:18px">HTTP Health Check</span></strong></p> <p>The seven-layer health check uses HTTP detection to obtain status information. If you choose to use HTTP health check, make sure that the <strong>Check Path</strong> is an accessible path. The accessible path at least ensures that HTTP requests can return 2xx, 3xx return values. If there is no accessible content under the health <strong>Check Path</strong>, the check may prompt a return value of 4xx. If the prompt fails, the server will be displayed as <strong>Disconnected</strong>.</p> <p>You can test on the back-end server by themselves before starting the HTTP health check.</p> <p><span style="font-size:16px"><strong>Examples for Test Methods: </strong></span></p> <p>curl -i -vvv http://10.1.1.25:80/app</p> <p>&bull;&nbsp;&nbsp;&nbsp;&nbsp; 10.1.1.25 is the host address, replace it with the host address in your pool.</p> <p>&bull;&nbsp;&nbsp;&nbsp;&nbsp; 80 is the server back-end port number, replace it with your server back-end port number, which is the port number you filled in when adding the host to the pool.</p> <p>&bull;&nbsp;&nbsp;&nbsp;&nbsp; /app is the inspection path, replace it with the <strong>Check Path</strong> you filled out when configuring the health check.</p> <p>&nbsp;</p>