[ovirt-devel] Thoughts on modularization

[Alon Bar-Lev]

----- Original Message -----
> From: "Vojtech Szocs" <vszocs at redhat.com>
> To: "Alon Bar-Lev" <alonbl at redhat.com>
> Cc: devel at ovirt.org, "Mark Proctor" <mdproctor at gmail.com>
> Sent: Wednesday, November 5, 2014 5:24:14 PM
> Subject: Re: [ovirt-devel] Thoughts on modularization
> 
> 
> 
> ----- Original Message -----
> > From: "Alon Bar-Lev" <alonbl at redhat.com>
> > To: "Vojtech Szocs" <vszocs at redhat.com>
> > Cc: devel at ovirt.org, "Mark Proctor" <mdproctor at gmail.com>
> > Sent: Wednesday, November 5, 2014 4:12:06 PM
> > Subject: Re: [ovirt-devel] Thoughts on modularization
> > 
> > 
> > 
> > ----- Original Message -----
> > > From: "Vojtech Szocs" <vszocs at redhat.com>
> > > To: devel at ovirt.org
> > > Cc: "Mark Proctor" <mdproctor at gmail.com>
> > > Sent: Wednesday, November 5, 2014 5:04:24 PM
> > > Subject: [ovirt-devel] Thoughts on modularization
> > > 
> > > Hi guys,
> > > 
> > > I've discussed this recently with Yair and Mark, I just wanted to share
> > > some more thoughts on this topic -- in particular, how modularization
> > > problem can be approached (regardless of implementation details).
> > > 
> > > I see two approaches here. The typical one is to define APIs for modules
> > > to consume. For example, oVirt Engine extension API has API for auth
> > > stuff; oVirt UI plugin API has API for showing tabs and dialogs, etc.
> > > The advantage is strict consistency, disadvantage is burden of having
> > > to maintain the whole API. With this approach, you tell modules: "This
> > > is the API to work with system, defining how you can plug into it."
> > > 
> > > Now turn 180 degrees. The other approach, which is really interesting,
> > > is to let modules themselves export API. This naturally leads to module
> > > hierarchies. Ultimately, this leads to micro-kernel-style development,
> > > where all logic resides in modules. Now you might ask: "What if we want
> > > to employ some consistent work flow across multiple modules? For example,
> > > have some pluggable *auth* infra?" -- this can be done via some "higher"
> > > level module, that exports API and "lower" level modules consume that
> > > API.
> > > 
> > > If you have any ideas, please share!
> > 
> > Both solutions can be applied using existing extension api, an extension
> > can
> > locate other extension and interact with it the same way the core interacts
> > with extensions.
> 
> But how does core interact with extensions? I assume via well-defined
> API, i.e. in accordance with first approach mentioned above.

presentation:
http://www.ovirt.org/File:Ovirt_3.5_-_aaa.pdf

package org.ovirt.engine.api.extensions;

/**
 * Interface of an extension.
 */
public interface Extension {

    /**
     * Invoke operation.
     * @param input input parameters.
     * @param output output parameters.
     *
     * <p>
     * Interaction is done via the parameters.
     * Exceptions are not allowed.
     * </p>
     * <p>
     * Basic mappings available at {@link Base}.
     * </p>
     *
     * @see Base
     */
    void invoke(ExtMap input, ExtMap output);

}

> With second approach mentioned above, core would not interact with
> extensions at all (or in a very limited way), instead - extensions
> would interact with each other. In other words, extension would not
> need to implement core-specific API (there would be none), instead
> it would inject its dependencies (other modules/extensions) and
> consume their APIs. This is the difference I wanted to point out :)

The extension interface is primitive to enable exactly that, provided java people will open their minds :)

Regards,
Alon