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[Stuart Bishop <stuart.bishop@xxxxxxxxxxxxx>]

I've refactored this into parts and added the client side code I think
we need. I've also added ZeroMQ as an alternative transport.

Branch is at lp:~stub/+junk/gpgverify

Random thoughts:

ZeroMQ seems to do what it says on the tin.

Unlike HTTP, we need to define our own protocol. This gives us more
flexability, but also more to think about.

HA story is the same (by putting servers behind HAProxy), or better
(we could plug in our own broker which whatever features we can dream
up, such as persistent queues or services registering themselves
instead of hard coded addresses and ports).

ZeroMQ doesn't need Apache. With ZeroMQ, we can write and test our own
HA and failover stories. This is very difficult when HA and failover
requires HAProxy. But HAProxy probably provides a good enough story
for us, is already production ready and has a decent admin interface.

ZeroMQ services need ipfilter configuration to open the port. HTTP
services need HAProxy & Apache love, and possibly the ipfilter config
too if Apache is not local.

If we are putting together complex services, I think ZeroMQ would be a
win. But at least at this stage, I think we want simple services and
the HTTP services are less of a surprise. I personally am leaning
towards whatever is easiest to deploy and maintain, as from the dev
side there seems little real difference. If we abstract out the
transport in a similar way to my example code, there will be no
difference. ZeroMQ would have a superior deployment story if we put
the effort into a common broker and had services register themselves
as they come up and down, but not by much since there isn't much work
adding the new service to the HAProxy configuration.

-- 
Stuart Bishop <stuart@xxxxxxxxxxxxxxxx>
http://www.stuartbishop.net/