Hi there, I’m looking into this - and indeed, is a little confusing.
This setting should be used in conjunction with
When Tyk initiate keep-alive connection, DNS query made only once per connection but there could be many connections in request pool.
In some cases, when upstream instance is removed from load balancer, but not terminated, it continues receiving traffic from Tyk, since the TCP connection is still active, and nobody terminated it.
This option forces connection to be re-created after a specific amount of time, so Tyk will establish connection to new valid upstream instance.
This is quite specific case, since in most of the cases, when the instance is removed from LB, connection is terminated properly.
So while it does not directly relate to DNS caching, it solves related issue caused by IP caching.