I'm trying to create a proxy server using regional external application load balancer and regional internet NEG(FQDN) but facing error 503 and showing "no healthy upstream" when sent request to the IP address. It was working fine with global application load balancer and internet NEG. The purpose I'm trying to achieve is to allow static external IP for whitelisting the outbound IP to the main server.
Backend services provide configuration information to the load balancer. Load balancers use the information in a backend service to direct incoming traffic to one or more attached backends.
As per the Official Google cloud document (See the table),Global external Application Load Balancer supports internet NEG(FQDN) but Regional external application load balancer does not support internet NEG(FQDN) backend service.