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From Peter Johnson <pe...@wizardslair.net>
Subject Re: Systems Architecture Pros and Cons
Date Thu, 13 Oct 2005 23:01:58 GMT
> If you measure the resource util on the apache boxes while under load,
> you may find that you can get by with A single apache instance and 4 tomcat instances
(each on it's own box).

You may be able to but you lose the ability to load balance across the 
Apache instances for high-availability.

> It does depend on the balance of the workload between the apache and
> tomcat.  The tomcat/jvm generally needs a lot of cpu. 

In many regards this isn't an issue for either layout because if it is 
found that the load is too much one just adds another server. But this 
does raise a valid argument for the N + M configuration as it allows for 
different hardware to be deployed for Tomcat e.g. more RAM or a second 
CPU. However most larger deployments prefer to maintain a standard 
server build for all servers and simply use server count to increase 
capacity in which case I guess the flat single tier is preferable.

> Are you going to store the tomcat content N times (once per box) or use
> a single instance of shared storage?

The option for data management really depends on the type and volume of 
data. Load balancing NFS can be problematic and clustered filesystems 
expensive but it may be the best solution. Syncing out data files (e.g. 
XML) to each server is another alternative. This is really very 
dependent upon the nature of the application and type of the data.

Another option some may use is a central DB from which local files are 
generated based on access or a background task.

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