Troubleshoot your Classic Load Balancer

The following tables list the troubleshooting resources that you'll find useful as you work with a Classic Load Balancer.

API errors

Error
CertificateNotFound: Undefined
OutofService: A transient error occurred

HTTP errors

Error
HTTP 400: BAD_REQUEST
HTTP 405: METHOD_NOT_ALLOWED
HTTP 408: Request timeout
HTTP 502: Bad gateway
HTTP 503: Service unavailable
HTTP 504: Gateway timeout

Response code metrics

Response code metric
HTTPCode_ELB_4XX
HTTPCode_ELB_5XX
HTTPCode_Backend_2XX
HTTPCode_Backend_3XX
HTTPCode_Backend_4XX
HTTPCode_Backend_5XX

Health check issues

Issue
Health check target page error
Connection to the instances has timed out
Public key authentication is failing
Instance is not receiving traffic from the load balancer
Ports on instance are not open
Instances in an Auto Scaling group are failing the ELB health check

Connectivity issues

Issue
Clients cannot connect to an internet-facing load balancer
Requests sent to a custom domain aren't received by the load balancer
HTTPS requests sent to the load balancer return "NET::ERR_CERT_COMMON_NAME_INVALID"

Instance registration issues

Issue
Taking too long to register an EC2 instance
Unable to register an instance launched from a paid AMI