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From David Lutterkort <>
Subject Re: design question about cimi system's subcollection implementations
Date Tue, 26 Feb 2013 22:27:20 GMT
Hi Dies,

I am not 100% sure I understand what you are suggesting, but I think you
are saying that the instances method in each driver should support an
additional filter param 'system_id' .. is that correct ?

As I understand it, the find method in CIMI::Model::SystemMachine needs
to accept a system_id param to indicate what system we're looking at,
and that param would be passed to driver.instances, i.e.
SystemMachine#find would like something like

        def find(system_id, ctx)
          ctx.driver.instances(ctx.credentials, :system_id => system_id).map do |sm|

If so, I am all for it. Do we need a way to introspect whether instances
accepts a :system_id param ?


On Tue, 2013-02-26 at 21:46 +1100, Koper, Dies wrote:
> I'm looking at what the best way would be to design a cimi system's subcollections (SystemMachine
and SystemVolume in particular), and their mapping to the drivers.
> Retrieval of a system (or collection of systems), gives a response that includes e.g.
its machines:
>   <machines href="" />
> Listing the system's machines, should return a collection of SystemMachines, with references
to the actual machines.
> <Collection xmlns="" resourceURI="">
>   <id>http://localhost:3001/cimi/systems/system1/machines</id>
>   <count>2</count>
>   <SystemMachine>
>     <id>http://localhost:3001/cimi/systems/system1/machines/inst0</id>
>     <name>Mock Instance With Profile Change</name>
>     <description>SystemMachine inst0 for System system1</description>
>     <machine href="http://localhost:3001/cimi/machines/inst0" />
>    <operation rel="delete" href="http://localhost:3001/cimi/systems/system1/machines/inst0"
>   </SystemMachine>
> ...
> I'm considering several ways to implement this:
> 1. From system_machine#self.find, passing the system_id to the existing driver.instances
method to list only the instances of that system, then convert the instances into a SystemMachineCollection.
This would be the most efficient way for fgcp.
> 2. Introduce a driver.system_machines method and leave it up to the driver how to retrieve
the instances. A disadvantage is that each supporting driver relying on instances() would
have to do the instance->machine conversion themselves.
> 3. Introduce a driver.system_instances method and leave it up to the driver how to retrieve
the instances belonging to this system. The instance->machine conversion would be done
in system_machine#self.find as in 1. A disadvantage of this is the mixture of cimi and DC
> I prefer 1. Possibly by adding a "system" feature for the drivers that support this in
their instances (and storage_volumes, keys?) methods, so that we can use the DB for drivers
that don't.
> What do you think?
> Regards,
> Dies Koper
> --
> Dies KÖPER
> Software & Solutions Architect
> Fujitsu Australia Software Technology (FAST) - Cloud Computing
> Tel. +61 2 9452 9061 (Fujitsu internal 7985-29061)

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