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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Does Tomcat support clustering for automatic fail over?
Date Thu, 05 Nov 2015 22:10:02 GMT
Stephen,

On 11/5/15 10:49 AM, Stephen Booth wrote:
> On 04/11/2015 00:56, javier_espana@hna.honda.com wrote:
>> I would like to setup a couple of servers for automatic fail-over.  In case
>> one fails the other can take over.  Does Tomcat support that kind of setup?
>> If so, can you direct me to where I can find some documentation about it?
> 
> As others have commented fail-over is usually handled by the
> load-balancer but that still leaves the problem of the load-balancer as
> a single point of failure.
> 
> One trick is to use CARP
> https://en.wikipedia.org/wiki/Common_Address_Redundancy_Protocol
> to fail over between servers. In the freely available linux
> implementations this is not a substitute for a load balancer because
> only one server is active at a time. Strictly speaking this is
> redundancy of hosts not processes carp won't help you if the tomcat
> process dies but the node stays up.
> 
> The actual configuration we use is to have redundant apache servers with
> an ip address that fails over via CARP and then use apache as a load
> balancer to access the tomcat nodes.
> We don't really have the level of traffic to need a load-balancer but
> putting in fail-over at every level of the software stack reduces
> exposure to losing a process it also makes it easier to do work on the
> tomcat processes while keeping the service live.

I would argue that any production deployment ought to utilize a load
balancer and at least two servers, even if only to allow you to take one
of them offline for upgrades. Maybe you don't require 24x7 uptime, but
most production deployments do, and having a single box running
everything is simply not robust enough.

Note that "load balancer" can be any number of things, including an
industrial-strength piece of hardware to a simple httpd instance (which
has its own set of similar uptime issues).

-chris

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