The Mistake of Using DNS Caching for Monitoring Websites

DNS or Domain Name Server is the protocol on the internet that allows users to access websites by name instead of using their IP address. When a user tries to access website using its name, the browser connects to the destination web server to resolve its IP for that domain name. Once the DNS record is identified, the browser loads the page as requested by the user, leaving the DNS server free to deal with another request. Though the whole process takes only few milliseconds time for each DNS query, it can cause a overload on the server if unlimited simultaneous requests are made to reach the server. This can cause DNS failures making the site totally not reachable to the users or affecting the site performance by slowing down the responses to the DNS queries.

What is DNS Caching?

To reduce the unnecessary load of DNS lookup requests and have the faster retrieval of web pages, DNS caching is done by saving the data locally on the system. The initial request might take a few milliseconds longer but the subsequent requests are answered faster since the data is already cached locally. Every DNS record is associated with a TTL (Time to Live) value which determines how long a particular DNS record should be cached locally before a new copy of the record is retrieved from DNS. When a request is made for a website, it first refers to the cache to get the IP address for that domain name and if record is not found then the request would pass on to the DNS server.

Why Relying on DNS Caching Can be Bad for Monitoring Services?

Website monitoring service plays an important role in minimizing the website downtime. Generally, the monitoring service sends immediate alerts as soon as it encounters an issue with any of the parameters associated with the websites. But some monitoring services misguide website owners by giving wrong information on site's downtime because they use DNS caching to determine website availability. Here, the site outage will be known only after the TTL timespan gets elapsed. That means if TTL is set for 2 hours, and if DNS server encounters an issue in the meantime, it will be known only after site's time-to-live expires. This delay in identifying the outage is a loss to website owners, because there is a possibility of losing substantial business revenues during this downtime duration.

How a Quality Monitoring Service Works?

A quality monitoring service has a different approach to website downtime issues. The service adopts best methods to avoid delays in identifying the issues related to website downtime. As said, the quality service will not depend on DNS caching to determine outages of DNS servers. Regardless of the domain's TTL configuration settings, the site monitoring service would continuously track servers for uptime and alert promptly when any issue is identified that can affect website working.