What is Round-Robin DNS?

In the world of Internet infrastructure, there are many ways to distribute traffic across a number of servers. One such method is circular DNS. Round-robin DNS is a technique that distributes traffic among multiple servers by rotating through a list of IP addresses associated with a single hostname. While this approach may seem like a quick and easy way to distribute traffic, there are some significant drawbacks to consider.

What is Round-Robin DNS?

Round-robin DNS is a load-balancing technique in which balancing is done by a DNS server called an authoritative name server, rather than a dedicated piece of load-balancing hardware. Round-robin DNS can be used when the content of a website or service is hosted on multiple redundant web servers; When an IP address is requested from a DNS authoritative name server, the server assigns a different address each time, which works in rotation. This is especially useful when redundant web servers are geographically separated, making traditional load balancing difficult. Round-robin is known for its ease of implementation, but it also has strong drawbacks.

A DNS server with round robin enabled will have many different A records, each with the same domain name but a different IP address. Each time a DNS server is queried, it sends the last IP address it answered to the back of the queue, working round the clock. IP addresses in a round robin DNS server are like baseball players in a batting lineup: each takes a turn and then goes to the back of the line.

Why do you need Round-Robin DNS?

Load balancing is essential these days for huge web services that generate huge amounts of traffic. As you can imagine, web servers can easily become overloaded. For this reason, Round-Robin is definitely a good approach to avoid such occurrences. This is the correct way and one of the most used methods to split the traffic on your servers.

How does this work?

When using round-robin DNS, instead of using a dedicated load-balancing hardware element to distribute traffic, the authoritative name server will do the balancing.

Round robin only works when the content of a website or service is hosted on multiple redundant web servers. A server is already a copy of a system that includes communication lines and network devices. If the primary DNS server is running, it can act as the primary operating system.

When queried repeatedly for an IP address, the DNS authoritative name server returns a different IP address each time. It selects these addresses in rotation order:

• User #1 requests example.com and is redirected to the first IP address.
• User #2 sends a request to access example.com and is redirected to a second IP address.
• User #3 requests access to example.com and points to a third IP address.
• When user #4 also requests example.com, it is sent to the first IP address. This is how the round-robin algorithm works.

A DNS server with a round robin configuration has many different A records pointing to the same domain name while pointing to a different IP address. It works in a loop. Each time a DNS server receives a request, it sends the last used IP address behind the line.

Thus, the IP addresses in a circular DNS server work like the spokes of a bicycle wheel: each one falls perpendicular to the other.

Some benefits

• Easy to apply: Round-robin DNS is easy to implement and requires no special skills or knowledge.
• Improved scale: It distributes incoming traffic across multiple servers, which helps handle more requests and improves scalability.
• Load balancing: With this technique, the load is balanced between the available servers, which helps prevent any one server from becoming overloaded.
• High availability: Round-robin DNS helps ensure high availability by directing traffic to available servers. If one server goes down, traffic is automatically redirected to the remaining servers.
• Effective: Round-Robin DNS is a cost-effective solution for distributing traffic between multiple servers. It requires no additional hardware or software and can be easily configured.

Disadvantages

Unfortunately, Round-robin DNS also comes with a number of drawbacks.

• Uneven distribution of traffic: Due to DNS caching and client-side caching, it does not always succeed in evenly distributed traffic. When a user queries a high-traffic recursive resolver for a particular site, the resolver will cache the website’s IP and may continue to send large amounts of traffic to that IP.
• No fault detection: If one of the multiple servers is offline, the algorithm continues to use it and direct requests to it. Usually, its A note must be manually removed from the circuit. Otherwise, every time traffic is directed to a downed server, one unlucky user will be denied service.
• Equal priority: There are downsides to treating every application equally. With the round-robin DNS technique, you cannot prioritize processes, no matter how important they are.

The result

Although round robin DNS may seem like a simple and convenient way to distribute traffic across multiple servers, it has significant limitations that can negatively impact performance and user experience.

Load balancers provide a more robust and intelligent solution that overcomes these limitations and provides additional features and capabilities. So if you’re considering a traffic distribution solution for your website or application, a load balancer is almost always the better choice.