We are starting to experiment with Azure Traffic Manager and I have a question regard the TTL setting. I am wondering if there is any guidance on the pro's and cons to altering the default of this setting. In our case i would like the TTL to be as low as
possible so that when my hosted services goes offline my users will quickly get routed to a failover service. Since the default is 5 minutes and it takes Traffic Mgr at least 90 seconds to notice failure it would appear by default I have a 6.5 minute window
during which clients could be trying to access a failed service.
So I'd like to dial the TTL down to 60secs, so that I have a 2.5min outage window. But what are the downsides to this? Is it simply going to mean more DNS requests coming in to the Traffic Manager because the results will be cached for a shorter time?
We recommend you leave the setting at the default value of 300 seconds (5 minutes). More frequent times will increase the amount of traffic from clients and secondary DNS servers to Traffic Manager, potentially impacting the performance of clients or DNS
You may also find similar information in the Labs doc:
Note: The TTL determines for how long clients and secondary DNS servers cache a DNS host entry. Clients will
continue to use a given hosted service until its entry in the cache expires. For this hands-on lab, the TTL is set to the lowest possible value to allow policy results and changes in the status of services to be seen as early as possible.
Note, however, that lowering this value increases DNS traffic and that you should consider keeping its default value for your production services.
Using a low TTL value will cost more time for clients to get response even when services are all in normal status while using a high TTL value will make clients still access failed service when that service is down.