Clustering a DDD/CQRS/ES app

Hi,

I've been experimenting with a simple app (todo-list manager) where I 
want to try out CQRS/ES with a REST API on top. You can see the code at:
https://github.com/rickardoberg/cqrs (CQRS/ES library)
https://github.com/rickardoberg/stuff (todo list app)
https://github.com/rickardoberg/shithappens (app consuming Stuff REST 
API for automation)

Yesterday I looked into the question of "how would I cluster this?". The 
REST API creates commands and dispatches to a command handler that then 
invokes the domain. So what I did was to introduce a command handler 
filter that uses Hazelcast to distribute the command with global 
ordering into set of servers. All servers get the same sequence of 
commands, process them locally, generate the events, update the views. 
Tremendously simple, and works. The instance that published the command 
gets the result and/or exception from the command handler, and uses that 
to create a REST API response synchronously. If the REST client (e.g. a 
browser) is pinned to a server using cookies it gets a 
read-what-you-write guarantee. Awesome.

The main remaining issue is how to deal with failures, or bringing up a 
new server. Don't quite know the best way to handle that yet.

But my question is: if anyone else is clustering their CQRS/ES apps, how 
did you do it? Where did you put in the clustering, and how do you 
partition and handle failures etc.?

/Rickard


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