Troubleshoot connection issues

Available in Classic and VPC

You may encounter the following issues while using the Load Balancer service. Check the causes and solutions for each issue and take appropriate action.

Subnet connection error

• The Subnet to connect to doesn't appear in the Subnet list when creating a Load Balancer.
• Unable to connect to the Subnet when creating a Load Balancer.

Cause

Occurs when Subnet settings and Load Balancer settings do not match.

Solution

• Verify that you selected Load Balancer as the purpose when creating the Subnet.
• Check if the Subnet is dedicated to the Internet Gateway.
  • It should match the network status of the Load Balancer you're connecting to.
  • If the Load Balancer's network status is Private, the Subnet's Internet Gateway exclusivity should be set to N(Private). If the Load Balancer's network status is Public, the Subnet's Internet Gateway exclusivity should be set to Y(Public).
• Ensure you created the Subnet in the same zone where the Load Balancer is created.

503 error when accessing Load Balancer

• Unable to communicate with the Load Balancer.
• A 503 error occurs when accessing the Load Balancer.

Cause

• 5xx errors are Internal Server errors. It mainly occurs when applications in the target group are not responding (due to middleware or DBMS listener down, resource shortage due to overload, etc.).
• It may occur when the server and Load Balancer are not properly connected.

Solution

Please check the following items:

• Re-check each server that composes the service.
• Verify the Health Check status of the Load Balancer Target.
• Check if the Load Balancer Subnet range and service port are allowed in the target server ACG.
• For NLB, the Client IP is maintained when entering the server. Verify that you added the Client IP range to the Target server ACG.
• Ensure you didn't add conditions that could block load balancer-related traffic to the NACL of the Load Balancer Subnet.
• Check if the monitoring information of the Load Balancer Target group is normal.
• Verify that the service port is operating normally on the server set as the Load Balancer Target (Target server).
• Check that Load Balancer requests are not being blocked by the internal firewall on the server.