What is DNS Server Load Balancing?

DNS Server Load Balancing is an architecture where Domain Name System (DNS) servers are placed behind a Server Load Balancing system. DNS requests are distributed, or load balanced, across a group of DNS servers. This provides a highly available and high performing DNS infrastructure.

DNS technologies provide a built-in load balancing solution based on the DNS protocol specification. Multiple DNS servers are often deployed, and clients performing DNS queries are presented a list of IP addresses for every DNS server. The DNS client protocol will attempt to query the first DNS server, and if this query fails, will fail-over and attempt the query on the next DNS server.

This DNS standard solution works well enough for most network environments. The downside with the standard DNS failover mechanism is when one or more of the DNS servers is not responding to DNS queries, the client will pause until the request times out. This timeout period depends on the client system. Typical timeout periods are 15 seconds or more. In modern networks, 15 seconds is an extremely long time.

There are classes of network infrastructures where the standard DNS failover mechanism is unacceptable. These environments include:

  • Internet Service Provider (ISP) networks which provide DNS as part of their core services. Any DNS server failure would create unacceptable performance issues for customers.
  • High volume network infrastructures such as network carriers, cloud service providers, high transaction data center environments and other large service provider infrastructures.
  • Infrastructures with high end-user performance requirements like stock traders, online store businesses, etc.
  • Infrastructures with Global Server Load Balancing (GSLB) implementations

DNS Server Load Balancing Benefits

DNS Servers placed behind Server Load Balancers or Application Delivery Controllers is a “best in class” architecture for mission critical infrastructures. DNS queries are simple UDP connections on port 53 and relatively simple to deploy. The benefits of this architecture include:

  • Failed or unhealthy DNS servers are monitored by the ADC load balancing systems and almost instantly removed from client query requests.
  • DNS servers can be removed from service live for maintenance without affecting existing customers
  • DNS services can be scaled-out dynamically without updates to DNS name services. All servers are behind a single external IP, and additional services can be added dynamically.
  • High-volume DNS services are load balanced based on performance and load. Traditional DNS uses a round-robin approach with no server loading or health visibility.

Related Terms

How A10 Can Help

A10 Networks Thunder Series of Application Delivery Controllers is deployed in most of the world’s largest carrier network and service provider networks.

A10 devices are built using an in-depth strategy, with key protections integrated within our Thunder Series ADCs. Our ADCs are compatible with a variety of different firewall vendors, allowing you to deploy our devices right away with your existing corporate defense systems and adequately secure your network.

Learn more about the A10 portfolio of high-performance ADCs. Download the white paper Evolution of ADCs: The A10 Advantage Over Legacy Load Balancers.