Apologies for the long post!
I’m working on an application which is standard Rails fare:
database-centric, hosted, with RESTful (-ish!) controllers exposing
methods as web services. Nothing out of the ordinary.
But at some point I’m going to run into a barrier as my audience is
quite conservative and certain organisations that form a very important
part of my target audience will want, and probably demand, the ability
to deploy their application onto their own servers, even if they end up
using the hosted service day-to-day. This is no huge business obstacle
as I intend to open-source the app anyway. Naturally, I’d hope and
expect the majority of clients to use the hosted version. The reality is
that they are more likely to if they know that they can use the app
locally if the company managing the hosted version goes belly-up.
However, what I don’t want is all the data they are storing in the
locally-deployed app to be locked away from the outside world. Although
they may be entering data into their own deployment, I’d like the
centrally hosted application to keep a read-only cache of their data as
up-to-date as possible, at least updated once every 24 hours, and make
it available to other users to the extent the owner of the data permits
(these rules are embedded in the app already, so “all” that would be
required is for the ‘slave’ deployment to communicate updates to the
‘master’). Naturally clients would have the ability to turn off this
synchronisation.
RDBMS-native replication doesn’t seem to make sense as I have no control
over the application deployments. I’m looking at using web services to
communicate updates from one deployment to another, but would rather
avoid re-inventing the wheel as I can imagine this getting tricky
quickly. Are there proven architectures for this situation? Should I be
looking to simultaneously update the local and remote application or
batch updates each day? I’m not talking about high volumes of data or
large number of deployments. And I don’t want to over-engineer an
architecture that I hope will be used very little!
Any thoughts very welcome as I go into this,
Toby