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From Oleg Kalnichevski <ol...@apache.org>
Subject Re: looking for reliable failover pattern
Date Sat, 28 May 2011 15:47:45 GMT
On Thu, 2011-05-26 at 20:17 -0400, Dan Checkoway wrote:
> Hello,
> I'm looking for recommendations on best practice for client side
> failover...with pooling/keepalive.  I've been rolling my own, but I'm
> migrating to HC and could use some advice.  Here's what I'm faced with
> requirements-wise:
> 1. My app is running on appserver01...n, and it's using HttpClient to
> talk to a web service that's running on ws01...n.
> 2. Unfortunately, my hands are tied and I can't throw a VIP/LB in
> front of ws01...n (wouldn't that just be too easy), and I can't use
> round-robin DNS either (I found MultihomePlainSocketFactory, but it's
> deprecated anyway).  I need to address the ws* boxes individually.
> 3. A key requirement is that I take advantage of persistent HTTP
> connections (keepalive).
> 4. When appserverN needs to talk to ws*, it should pick a node at
> random (poor man's load balancing).  If that node is down, it needs to
> fail over to another node, without the calling code knowing or caring
> what happened.
> Is there a reliable existing pattern or example out there somewhere,
> or -- better yet -- something in HttpCore or HttpClient that provides
> this type of pooling with failover strategy out of the box?  I would
> rather steal or adapt good code than reinvent this wheel...
> Any tips?
> Thanks,
> Dan


HttpClient 4.1 supports fail-over based on multiple DNS entries (so
called multihoming) out of the box. This is actually the reason
MultihomePlainSocketFactory got deprecated. 

Does your application need to support fail-over to a standby node only,
or you actually need to be able to 'spray' the traffic across multiple


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