The DNS Failover Service determines a server is down based on the monitoring type you’ve selected and configured. For example, if you’ve created a PING monitor and assigned that to your server, as soon as it stops pinging and exceeds the test “interval” and “retries” values you’ve specified, it will be considered “down” and subject to failover or removal.
If you are using the HTTP method to monitor your website using the failover system, the monitoring service will look for the HTTP information codes coming back from your web server and accept the one(s) you have specifically set as acceptable. For example, if it receives a 200 code back (which means OK and is accepted by default), then it will consider the website to be up and ok. It really doesn’t matter what content your page sends back. If your site sends back any of the error codes, such as a 301 (redirect), 403 (forbidden), 404 (not found), 408 (timeout), 500 (internal server error) or any other type of error, it will consider the response a failure and will change the ‘A’ record to one of your other IP addresses (if you are not using round robin) or simply remove that ‘A’ record for that particular IP address (if you are using round robin).
It is important to note that the failover service will NOT fail over to one of the other IP addresses if they are not currently reporting an “UP” status. If your second IP is also in a failure state, the service will not change your ‘A’ record because doing so would not improve the situation for your end-users. If, however, one of the secondary IPs did come back while the primary is still down, it will change over.
Configuring failover can be challenging at times. Please do not hesitate to reach out to use for assistance. We’re here 24×7 to help you!