Re: [ovirt-devel] Thoughts on modularization

From: "Vojtech Szocs" <vszocs(a)redhat.com&gt; To: "Alon Bar-Lev" <alonbl(a)redhat.com&gt; Cc: devel(a)ovirt.org, "Mark Proctor" <mdproctor(a)gmail.com&gt; Sent: Wednesday, November 5, 2014 5:24:14 PM Subject: Re: [ovirt-devel] Thoughts on modularization ----- Original Message ----- > From: "Alon Bar-Lev" <alonbl(a)redhat.com&gt; > To: "Vojtech Szocs" <vszocs(a)redhat.com&gt; > Cc: devel(a)ovirt.org, "Mark Proctor" <mdproctor(a)gmail.com&gt; > Sent: Wednesday, November 5, 2014 4:12:06 PM > Subject: Re: [ovirt-devel] Thoughts on modularization > > > > ----- Original Message ----- > > From: "Vojtech Szocs" <vszocs(a)redhat.com&gt; > > To: devel(a)ovirt.org > > Cc: "Mark Proctor" <mdproctor(a)gmail.com&gt; > > 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.

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 :)