bob-barrett commented on pull request #9902:
URL: https://github.com/apache/kafka/pull/9902#issuecomment-771823264


   > For instance, we could try all the resolved IPs before applying the 
backoff. However, we would still have to wait until the connection timeouts for 
each IP.
   
   @dajac That's right, and that's my concern with exhausting the 
currently-resolved IPs. The default connection setup timeout is 10 seconds. 
Even without applying the backoff, 10 seconds of delay per additional IP 
address is pretty noticeable.
   
   > Also, I suppose that we assume that closing connection is rather 
infrequent in normal circumstances so the cost of the DNS resolution is low. On 
the other hand, we relies on the DNS cache if the resolution happens really 
frequently. Am I getting this right?
   
   I think this is the right way to think about it, yes. There's already a DNS 
cache, which can be configured as needed. We're effectively adding our own 
additional cache (with a very long TTL) on top of that by preserving the 
resolved IPs. If a client has been connected to a server for hours or days and 
then disconnects, it makes complete sense to me to re-resolve DNS.


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