What are Traffic Manager "DNS Queries"?
Whenever a user accesses your application, a DNS query is used to map the name of your service to its IP address. By providing different responses to different DNS queries, Traffic Manager allows you to route incoming traffic across multiple hosted Azure services whether they're running in the same datacenter or across different datacenters around the world.
Traffic Manager provides you with a choice of traffic routing methods, including performance, failover, and round-robin. By using these to effectively manage your traffic, you can ensure high performance, availability, and resiliency of your applications.
Related questions and answers
Traffic Manager enables you to improve the availability of your critical applications by monitoring your hosted Azure service endpoints and providing automatic failover capabilities when a service goes down.
To do this, Traffic Manager continually monitors the health of each service endpoint. When these “Health Checks” detect that a service has gone down, Traffic Manager re-routes traffic to the other services.
Yes, the prices for DNS queries and health checks are the same irrespective of the traffic routing method used.
When a user's PC makes a DNS query, it doesn't contact the Traffic Manager name servers directly. Instead, these queries are sent via recursive DNS servers run by enterprises and ISPs. These servers cache the DNS responses, so that other users' queries can be processed more quickly. Since these cached responses don't reach the Traffic Manager name servers, they don't incur a charge.
The caching duration is determined by the "TTL" parameter in the original DNS response. This parameter is configurable in Traffic Manager—the default is 300 seconds, and the minimum is 30 seconds.
By using a larger TTL, you can increase the amount of caching done by recursive DNS servers and thereby reduce your DNS query charges. However, increased caching will also impact how quickly changes in endpoint status are picked up by users, for example, your user failover times in the event of an endpoint failure will become longer. For this reason, we don't recommend using very large TTL values.
Likewise, a shorter TTL gives more rapid failover times, but since caching is reduced the query counts against the Traffic Manage name servers will be higher.
By allowing you to configure the TTL value, Traffic Manager enables you to make the best choice of TTL based on your application's business needs.