Explanation
A 503 Service Unavailable Error is an HTTP response status code indicating that a server is temporarily unable to handle the request. This may be due to the server being overloaded or down for maintenance.

Managing Traffic Management GEOLOCATION Steering Policies
Geolocation steering policies distribute DNS traffic to different endpoints based on the location of the end user. Customers can define geographic regions composed of originating continent, countries or states/provinces (North America) and define a separate endpoint or set of endpoints for each region.
The Health Checks service allows you to monitor the health of IP addresses and hostnames, as measured from geographic vantage points of your choosing, using HTTP and ping probes. After configuring a health check, you can view the monitor's results. The results include the location from which the host was monitored, the availability of the endpoint, and the date and time the test was performed.
Also you can Combine Managing Traffic Management GEOLOCATION Steering Policies with Oracle Health Checks to fail over from one region to another The Load Balancing service provides health status indicators that use your health check policies to report on the general health of your load balancers and their components.
if you misconfigure the health check Protocol between the Load balancer and backend set that can lead to not get an accurate response as example below If you run a TCP-level health check against an HTTP service, you might not get an accurate response. The TCP handshake can succeed and indicate that the service is up even when the HTTP service is ly configured or having other issues. Although the health check appears good customers might experience transaction failures.