Whatever we do, there will be failures. The computer can break down; the connection can get saturated; a bug can cripple a server, or whatever other reason can lead to a big problem. But can a person stay 24-hour a day monitoring our DNS servers? There is a better solution, a service that will monitor your DNS traffic and act if there is a problem, and it is called DNS Failover.
DNS Failover explained
The DNS Failover is a system that monitors the traffic and event reaction that automatically switches your DNS records if a server goes down, so your visitors get a new IP address of another server that is still up.
That way, your domain will still be available through another IP address of one of the additional DNS servers.
First, there is a monitoring system. It could be checking the traffic or directly the DNS server with a command like a ping in a particular interval. In case there is too substantial traffic, or the DNS server stopped responding to the ping, an event will happen.
This event will trigger a reaction in your DNS. The reaction could be passive if you only want to get notified.
There is also a chance to set it up to deactivate the DNS record only.
The best is to replace the IP addresses.
Your DNS Failover will change the IP address in the DNS records and redirect to one of the rest DNS servers that are still up. If you have GeoDNS, you can have a server per continent, and if the one in Europe is down, the traffic will be redirected to the closest still working in Asia.
Some of the DNS Failover services have a mechanism to refresh the DNS records yet again when your previously down DNS server gets up and running again.
Benefits of DNS Failover
- Constant monitoring of your DNS. If there is a problem, you will know. You can choose what kind of monitoring to perform like ping, HTTP, HTTPS, TCP, and UDP. You can also decide which region you want to be monitoring.
- Stay up. Even if a server goes down, the load balancing mechanism will redirect the traffic to another IP address. And it will auto-update when the server gets up again.
- Ease of use. Most DNS providers have a very easy DNS Failover setup procedure. You can set it up in no time and have a better DNS network.
Problems with DNS Failover
When a user visits a site, the DNS records (A, AAAA, or others) will be stored in the browser cache for the period that the TTL value indicates. If you have a DNS Failover, you want low TTL values, but there could be a time period, for example, 5-10 minutes, when your user’s DNS records will still direct to the server that is down.
The period is small, and you can lower the TTL values, but you should think about it.
It is an additional cost to your typical DNS plan, but being able to just stay relaxed, knowing that your DNS provider will react in case of a problem, is worth it. If you have a backup, your client will not have any problem, and you can check what happened to the server that is not responding when you have time.