Gentlemen,
We discussed how to model state transitions in the ReST API in the Tech
Cabal and also offline for those who had particularly strong views. One
of the objections brought forward was how to distinguish between clients
(end users or applications) requesting state changes. For example: A
developer decides he wants to terminate his running instances and system
services that are used to notify conductor of when an instance has
changed state. For example db-o-matic wants to tell conductor that the
instance has now started.
After some deliberation offline between myself and sseago and without
objections from the Tech Cabal. We decided that the services and the
end users should access different APIs and we should not add complexity
into the end user API in order to support these system services.
With this behind us. We then were able to move forward to make a
decision on how to handle requests from a user to transition between
states. Like in the developer example above.
It was agreed that treating the State on an instance as simply an
attribute on the resource (and not an action) was more inline with the
ReST principal (Since adding actions breaks ReST principal of having a
unified interface - in our case the unified interface is defined by HTTP).
So, this now brings us to how we should represent these resources. I
think this is something that can and should be decided on list. I have
included below my opinion on how this should be represented, please add
in your own comments.
==
So in my opinion we should model a state machine as an independent
resource. When client wants to change the state of an instance, it
looks at the state machine to figure out what are the possible states I
can move to now. The instance can hold a reference to it's current
state and the state machine.
A simple example here: https://gist.github.com/4257951
Regards
Martyn
