DNS Failover explained

In the best-case scenario, your DNS will always work perfectly. The name servers will be up all the time, and your visitors will get their queries resolved without any problem. Sadly the perfect case does not exist. Sometimes servers go down. Here comes the DNS Failover. It is a simple mechanism to redirect the traffic in case of a failure.

DNS Failover and how does it work

DNS Failover is a mechanism in case of a problem with a particular DNS name server. It gets triggered, and it will auto-perform action such as change the DNS A records (the IP addresses) or only notify the administrator.

  1. You have DNS records for your domain. Let’s see just the A DNS records for this example. Those records link your domain to its addresses. Other typical records that benefit from the DNS Failover are the AAAA records and the SRV records.
  1. You will need to set a DNS monitoring that works with your DNS Failover. The monitor will periodically check the availability of your DNS server. Usually, it is a simple ping to see if they are responding. You can regulate the time interval between the probes. Other popular monitoring methods are using web checks, TCP, or UDP for the probes.
  1. If the monitor system detects down servers, it will trigger the DNS Failover, and it will auto-change the A records that lead to the down server with others (backup) that you predetermined. It will push the update across your DNS servers. You can set what action exactly the Failover should do. Just notify, just remove the IP address or change the IP addresses. You can also set the value, based on the % of lost packets, when exactly is the moment to trigger an action. In some cases, you can trigger the IP address change when your server is losing 50% of the packets, not 100%.
  1. The same monitoring system will be checking when the down server gets back up. When that happens, it can change the DNS records again and propagate the update to the rest of the servers. The system will get back to its normal state automatically, without any human interaction. That way, the downtime is experienced by a tiny group of visitors before the records get updated. You will have a lot better uptime, and your visitors can have a good experience. Of course, you can just set to notify when the server is back without changing the IP address.

Why should you care about DNS Failover?

Because it makes the life of a DNS administrator easier! If your website or application is down, you don’t need to do anything. Just sit down and relax. In a few minutes, depending on the frequency of the DNS monitor checking, you will be back online. No need for manually changing DNS records and waiting for DNS propagation.

If your downtime only lasts a few minutes, you will continue to receive visitors on your site or users on your application, relatively uninterrupted. That means they can continue using what they want, buy or do other activities.

It is easy to setup. Just activate it for the records you want, like A or AAAA records, by adding the additional IP addresses in case of failures.

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