This topic describes why a Server Load Balancer (SLB) instance fails to be accessed from a client and how to troubleshoot the issue.
|1||SLB cannot be accessed by backend servers. For Layer 4 SLB, an ECS instance cannot provide services for clients and function as the backend server of the SLB service at the same time.||N/A|
|2||A health check exception occurs.||For more information about how to troubleshoot health check exceptions, see How do I troubleshoot health check exceptions of a layer-4 (TCP/UDP) listener? and How do I troubleshoot a health check exception of a Layer 7 listener (HTTP/HTTPS)?.|
|3||SLB does not support FTP, TFTP, H.323, and SIP protocols.||
|4||The internal firewall of the server does not allow traffic on port 80.||You can run the following commands to temporarily disable the firewall to perform
|5||A backend port exception occurs.||
|6||The rp_filter feature conflicts with the policy-based routing mechanism of the Linux Virtual Server (LVS) for SLB.||
|7||A listener exception occurs.||
Run the following commands on the server. If you can see the listening information of 10.11.192.1:80 or 0.0.0.0: 80, the listening on the port is normal.
|8||No listeners are configured for the SLB instance.||Configure one or more listeners. For more information, see Listener overview.|
|9||The SLB instance cannot be accessed by using its domain name. This may be caused by an error in domain name resolution.||N/A|
|10||An exception occurs on the on-premises network of the client or the intermediate link of the service provider.||Test the connectivity on the service port of the SLB instance in different regions
and network environments.
If the exception occurs only when the SLB instance is accessed from the on-premises network, it can be determined that the problem is caused by a network exception. You can perform ping and MTR tests for further troubleshooting and analysis.
|11||The client IP address is blocked by Alibaba Cloud Security.||
|12||After you switch from Anti-DDoS Pro or Anti-DDoS Premium to Anti-DDoS Basic, the whitelist is not disabled.||Disable the whitelist.|
|If your problem persists, submit a ticket and provide the following information: