Traffic Router 4.0 dns.max-threads tuning

[Rawlin Peters <ra...@apache.org>]

Hey folks,

With TR 4.0, you can run into issues hitting max JVM thread/memory
limits if your `dns.max-threads` setting in
/opt/traffic_router/conf/dns.properties is set too high. Due to the
addition of the DNS Bounded Queue feature in 4.0, the DNS handler
thread count has effectively doubled.

The default for this value is 1000, which should be fine for most
environments, but I recommend trying out different settings in your
environment to see what gives you the best results. We had it set
originally to 10000 in our environment, and upon upgrading to 4.0, we
began to see TR unable to allocate new threads and crash due to lack
of memory. If your environment experiences a high percentage of TCP
DNS requests, you may hit the thread/memory limits sooner.

Best,
Rawlin