Update: the setting described in this post has since changed. See DNS SERVFAIL Errors for what SERVFAIL errors are, and how to configure DNS Check's current ServFail error notification threshold.

We noticed an interesting thing when analyzing the DNS errors that DNS Check has logged. 57% of the errors are of the "ServFail" variety, and of those, the vast majority are resolved 5 minutes later, when the record is next checked.

A ServFail error occurs when there's an error communicating with the DNS server. This could occur for a number of reasons, including an error on the DNS server itself, or a temporary networking issue.

Fortunately, most domains use multiple authoritative DNS servers, so if there is a short lived ServFail issue on one name server which doesn't impact the others, DNS lookups should still work. That said, if a name server has chronic ServFail issues, we recommend investigating why. ServFail errors happen, but should be rare.

Some of our customers are using DNS Check to page them when there's a DNS lookup failure. Of those, some do want to be notified if there's a short lived error that leads to a ServFail error, but others would rather not be paged, unless the error occurs more than once in a row.

Because of this, we've added a new option named "Suppress first ServFail notification" to the Notification Options page to suppress isolated ServFail errors:

Suppress first ServFail notification

If this option is turned on, the DNS checker waits until a DNS record has two or more consecutive ServFail errors before notifying you about them.

If this option is turned off, the DNS checker notifies you the first time a DNS record has a ServFail error.

Other failures, such as the wrong value being returned for a DNS record are not affected by this setting. As long as you have notifications enabled, you'll receive a notification the first time a non-ServFail error occurs.

You can turn this setting on or off for your account by going to the Notification Options page.