Troubleshooting an Unhealthy Backend Server

Scenarios

This section describes how you can use ELB self-service troubleshooting to detect and fix unhealthy backend servers in a timely manner.

Prerequisites

Before troubleshooting an unhealthy backend server, make sure you have completed the following:

• Creating a Backend Server Group
• Adding a TCP Listener
• Configuring a Health Check

Constraints

• You can only troubleshoot an unhealthy backend server.
• The backend server must be associated with a listener.
• IP as backend servers does not support self-service troubleshooting.

Procedure

1. Go to the load balancer list page.
2. In the navigation pane on the left, click Self-service Troubleshooting.
3. On the Elastic Load Balance tab, click Unhealthy backend servers.
4. Select the load balancer that has unhealthy backend servers.
5. Select the unhealthy backend server you want to troubleshoot.
6. Click Troubleshoot. On the displayed page, view the troubleshooting progress and details.

   View and rectify the faults in a timely manner as described in Table 1.

   Table 1 Health check items

   Health Check Category	Health Check Item	Reason	Suggestion
   Security group rule configurations	The protocol configured for the inbound rule	The inbound rules of the security group do not allow traffic over the health check protocol.	Change the security group rules by referring to the following: Security Group and Network ACL Rules Security Group and Network ACL Rules
   	The source configured for the inbound rule	The inbound rules of the security group do not allow traffic from the health check IP address to the backend server.
   	The port configured for the inbound rule	The inbound rules of the security group do not allow traffic over the health check port.
   	The protocol configured for the outbound rule	The outbound rules of the security group do not allow traffic over the health check protocol.
   	The destination configured for the outbound rule	The outbound rules of the security group do not allow traffic from the backend server to the health check IP address.
   	The port configured for the outbound rule	The outbound rules of the security group do not allow traffic over the health check port.
   Network ACL rule configurations	The protocol configured for the inbound rule	The inbound rules of the network ACL do not allow traffic over the health check protocol.	Change the network ACL rules by referring to the following: Security Group and Network ACL Rules Security Group and Network ACL Rules
   	The source configured for the inbound rule	The inbound rules of the network ACL do not allow traffic from the health check IP address to the backend server.
   	The source port configured for the inbound rule	The inbound rules of the network ACL do not allow traffic over all source ports.
   	The destination address configured for the inbound rule	The inbound rules of the network ACL do not allow traffic to the destination address.
   	The destination port configured for the inbound rule	The inbound rules of the network ACL do not allow traffic over the destination port.
   	The protocol configured for the outbound rule	The outbound rules of the network ACL do not allow traffic over the health check protocol.
   	The destination configured for the outbound rule	The outbound rules of the network ACL do not allow traffic from the health check IP address to the backend server.
   	The source port configured for the outbound rule	The outbound rules of the network ACL do not allow traffic over the health check port.
   	The destination address configured for the outbound rule	The outbound rules of the network ACL do not allow traffic to the destination address.
   	The destination port configured for the outbound rule	The outbound rules of the network ACL do not allow traffic over all destination ports.
   Health check configurations	The port configured for the health check	The specified health check port is different from that used by the backend server.	Use the backend port as the health check port by referring to Configuring a Health Check.

   

   • If all the check items are reported as normal, perform further checks as guided by How Do I Troubleshoot an Unhealthy Backend Server?
   • If the troubleshooting fails, click Troubleshoot Again or perform further checks as guided by How Do I Troubleshoot an Unhealthy Backend Server?

Popular Questions

• Why Is a Backend Server's Health Check Result Unknown?

  If a backend server group has health check enabled but is not associated with any listener, the health check result will be displayed as unknown.