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From Oleg Kalnichevski <ol...@apache.org>
Subject Re: Connection Pool and DNS Resolution timeout
Date Tue, 04 Mar 2014 14:14:26 GMT
On Mon, 2014-03-03 at 12:59 +0000, Alex, Joseph (Contractor) wrote:
> Hi,
> 
> We use HttpClient 3.1 and Httpcomponents 4.2.x in some of our apps with MultiThreadedHttpConnectionManager
and PoolingClientConnectionManager respectively. Some of our server endpoints use a Global
Name which can be switched to point to different data centers at runtime, depending on which
one is active (with the other DC still being "alive"). Example www.global.com<http://www.global.com>
which could either point to www.dc1.com<http://www.dc1.com> or www.dc2.com<http://www.dc2.com>.
When this switch was done, we noticed that the connections were not picking up the new DC's
IP and still routing to the old one. Assuming that the DNS resolution timeouts (networkaddress.cache.ttl)
is set to a low value in the JVM, would the connection pool honor this value and reset the
connections accordingly? . If they don't, what options do we have of ensuring that the connections
are reset, and recreated with the new DNS resolution, without having to restart the JVM?
> 
> Thanks,
> Joseph

Hi Joseph

HttpClient of all versions are fully reliant on the standard DNS
resolution mechanism provided by JRE. They also do not attempt to cache
or re-use resolved addresses, so 'networkaddress.cache.ttl' parameter
should have effect. 

Since HttpClient 4.2 though, one can plug in a custom DNS resolver
implementation [1] to replace or enhance the standard resolution
mechanism. 

Hope this helps

Oleg

[1]
http://hc.apache.org/httpcomponents-client-4.3.x/httpclient/apidocs/org/apache/http/conn/DnsResolver.html




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