What is Round-Robin DNS?

Round-robin DNS is a way to point one hostname at several servers and let DNS itself spread requests between them. Instead of a single A record, you publish multiple A records for the same name, each pointing to a different server, and the nameserver cycles through the order it returns them.

Because clients generally connect to the first address in the list, rotating that order means different visitors are steered to different servers. It requires no special hardware and no extra software, which is why it has been a go-to approach for decades.

Consider a name with three A records pointing to three web servers. As queries arrive, the nameserver rotates the order:

1. The first resolver to ask might receive the addresses in the order server A, server B, server C.
2. The next resolver receives server B, server C, server A.
3. The one after that receives server C, server A, server B, and the cycle repeats.

Each client typically uses the first address it is given, so over many queries the connections are spread roughly evenly across the three servers. The rotation is the whole mechanism, there is no awareness of load, latency, or whether a server is even alive.

Round-robin DNS is a good fit when you want simple distribution without standing up dedicated infrastructure:

• Basic load spreading across a pool of equivalent, stateless web or application servers.
• Distributing many independent resolvers, such as listing several mail exchangers or API endpoints of equal weight.
• A low-cost starting point for small sites that have outgrown a single server but do not yet need a full load balancer.

The simplicity that makes round-robin attractive also creates its weaknesses:

• No health checks. DNS keeps handing out a server's address even after it crashes, so a portion of users hit a dead endpoint until you edit the records by hand.
• Caching skews balance. Resolvers cache one answer for the duration of its TTL and serve it to every client behind them, so a single large resolver can funnel an outsized share of traffic to one server.
• No load awareness. Rotation ignores how busy each server actually is, so a heavily loaded machine receives the same share as an idle one.
• Slow to react. Removing a failed server only takes effect once cached records expire, and lowering the TTL to compensate increases query volume.

When you need smarter distribution, several approaches improve on plain round-robin:

• Load balancers sit in front of your servers, run real health checks, and route around failures in seconds rather than waiting for TTLs to expire.
• GeoDNS answers based on where the client is, sending users to the nearest region instead of rotating blindly.
• Managed DNS with failover combines health checks at the DNS layer with low TTLs to remove dead addresses automatically.

Whichever approach you choose, your records become critical infrastructure. ZoneWatcher watches them around the clock and alerts you the instant an address is added, removed, or changed unexpectedly.