----- Original Message ----- > From: "Michael Pasternak" <mpast...@redhat.com> > To: "Itamar Heim" <ih...@redhat.com> > Cc: "Vojtech Szocs" <vsz...@redhat.com>, "engine-devel" > <engine-devel@ovirt.org>, "Einav Cohen" <eco...@redhat.com> > Sent: Sunday, November 24, 2013 9:37:22 AM > Subject: Re: Using REST API in web UI - review call summary > > On 11/22/2013 12:00 AM, Itamar Heim wrote: > > On 11/21/2013 11:56 PM, Vojtech Szocs wrote: > >> > >> > >> ----- Original Message ----- > >>> From: "Itamar Heim" <ih...@redhat.com> > >>> To: "Vojtech Szocs" <vsz...@redhat.com>, "engine-devel" > >>> <engine-devel@ovirt.org> > >>> Cc: "Einav Cohen" <eco...@redhat.com> > >>> Sent: Thursday, November 21, 2013 10:25:04 PM > >>> Subject: Re: Using REST API in web UI - review call summary > >>> > >>> On 11/21/2013 11:18 PM, Vojtech Szocs wrote: > >>>> Hi guys, > >>>> > >>>> this is a summary of yesterday's review call, I'll try to highlight > >>>> important Q/A and things we agreed on. Feel free to add anything in case > >>>> I've missed something. > >>>> > >>>> -- > >>>> > >>>> Q: Why don't we simply try to use existing Java SDK and adapt it for GWT > >>>> apps? (asked by Michael & Gilad) > >>>> > >>>> A: This might be a viable option to consider if we wanted to skip > >>>> JavaScript-based SDK altogether and target Java/GWT code directly; we > >>>> could simply take Java SDK and customize its abstractions where > >>>> necessary, > >>>> i.e. using HTTP transport layer implementation that works with GWT. In > >>>> any > >>>> case, this would mean coupling ourselves to Java SDK (which has its own > >>>> release cycle) and I think this would complicate things for us. > >>>> > >>>> As proposed on the meeting, I think it's best to aim for JavaScript SDK > >>>> as > >>>> the lowest common denominator for *any* web application that wants to > >>>> work > >>>> with REST API. oVirt GWT-based UI can simply bind to JavaScript SDK, > >>>> i.e. > >>>> Java/GWT code that just overlays objects and functions provided by > >>>> JavaScript SDK. Another reason is ease of maintenance - I'd rather see > >>>> JavaScript SDK's code generation process to be independent of any other > >>>> SDK (people responsible for maintaining JavaScript SDK should have full > >>>> control over generated code). > >>>> > >>>> -- > >>>> > >>>> Q: What about functionality currently used by oVirt UI but not supported > >>>> by > >>>> REST API? (asked by Einav) > >>>> [For example, fetching VM entity over GWT RPC also returns related > >>>> data > >>>> such as Cluster name.] > >>>> > >>>> A: Based on discussion I've had with other colleagues after yesterday's > >>>> review call, I don't think that separate support-like backend layer is a > >>>> good idea. Instead, this is the kind of functionality that could be > >>>> placed > >>>> in oVirt.js library. Logical operations like "get VMs and related data" > >>>> would be exposed through oVirt.js (callback-based) API and ultimately > >>>> realized as multiple physical requests to REST API via JavaScript > >>>> Binding. > >>>> > >>>> oVirt.js client would be completely oblivious to the fact that multiple > >>>> physical requests are dispatched. In fact, since HTTP communication is > >>>> asynchronous in nature, oVirt.js client wouldn't even notice any > >>>> difference in terms of API consumption. This assumes JavaScript SDK > >>>> would > >>>> use callback-based (non-blocking) API instead of blocking one - after > >>>> all, > >>>> blocking API on top of non-blocking implementation sounds pretty much > >>>> like > >>>> leaky abstraction [1]. > >>>> > >>>> For example: > >>>> > >>>> sdk.getVmsWithExtraData( > >>>> callbackToGetExtraDataForGivenVm, // might cause extra > >>>> physical > >>>> requests to REST API > >>>> callbackFiredWhenAllDataIsReady // update client only when > >>>> all > >>>> data is ready > >>>> ) > >>> > >>> would this also resolve RunMultipleActions? > >> > >> Yes, I think so. There could be API to pass multiple "actions" and get > >> notified when they complete. > >> > >>> sounds like no reason to have RunMultipleQueries, although i'm still > >>> sure a single call to engine for multiple keys would be much more > >>> efficient than multiple async calls? > >>> (I understand we may not be able to model this). > >> > >> Efficiency-wise, yes, single call to get all data seems optimal. API-wise, > >> I don't think it really matters from oVirt.js client perspective. > >> > >> We can proceed with simple (possibly inefficient) solution and improve as > >> needed. We're making baby steps now.. > >> > >>> > >>>> > >>>> [1] http://en.wikipedia.org/wiki/Leaky_abstraction > >>>> > >>>> -- > >>>> > >>>> Last but not least, where to maintain JavaScript SDK projects: low-level > >>>> JavaScript Binding + high-level oVirt.js library. > >>>> > >>>> I agree that conceptually both above mentioned projects should go into > >>>> dedicated "ovirt-engine-sdk-js" git repository and have their own > >>>> build/release process. However, for now, we're just making baby steps so > >>>> let's keep things simple and prototype these projects as part of > >>>> "ovirt-engine" git repository. > >>>> > >>>> ... we can complicate things anytime, but we should know that any > >>>> complex > >>>> system that works has inevitably evolved from simple system that works > >>>> ... > >>>> (quote from http://en.wikipedia.org/wiki/Gall%27s_law) > >>> > >>> I think the entities should just be generated from the xsd. > >> > >> +1 > >> > >> The JavaScript Binding (aka low-level SDK) module should follow same > >> concepts as existing Java SDK - generated entities decorated with > >> operations to form fluent API. > >> > >> Everything Java SDK currently offers should be available in JavaScript > >> Binding. oVirt.js is our opportunity to build on top of that. > >> > >>> for the rsdl, makes sense to start with clean code to see what works > >>> best, then see about generating it (but you should adhere the rsdl as > >>> guidlines i guess). > >> > >> +1 > >> > >> The initial prototype should be written by hand, things will get generated > >> as soon as we have better idea how the end result should look like. > > > > i can understand that for the methods and maybe for populating the entities > > for the first few. > > the entities themselves, no point in hand coding - just generated them from > > the api.xsd. > > and once you decide how you want to fill them, not worth hand coding this - > > either json gives this out of the box, or should be generated as well. > > > >> > >>> > >>> lets try to plan for lightweight entities while at it - the API has a > >>> mechanism for different level of details - maybe we need a custom level > >>> where the client specifies which fields they want back or something like > >>> that. > >> > >> Good idea! We should definitely think about the granularity of entities. > >> > >> I didn't know REST API supports different level of detail per entity, is > >> there some documentation for this feature? > > currently it's about adding adding extra information (by supplying header > [1]), > this is driven by the properties that require extra query against the engine > to > fill them, > > obviously the default is [2] > > [1] All-Content: True > [2] All-Content: False
OK so if I understand correctly, "All-Content: False" (default) just returns data of given entity plus IDs of related entities, whereas "All-Content: True" returns data of given entity plus (embedded) data of related entities, is that correct? > > >> > >> Since JavaScript is dynamic, one possible solution would be to let client > >> define the entity structure (i.e. what data client needs) on the fly, > >> during runtime :) > > we talked about this solution couple of years ago, but it was obvious > that there is no real "demand" for it till UI moves to REST, I assume you mean to let client selectively specify properties of given entity when making REST call, correct? If yes, are you planning to support such feature? > > btw it won't solve the problem where to fill UI entity you need combination > of N REST entities, you still will have to perform N + 1 queries to API Of course. But we can make improvements with regard to: - optimizing queries so that client receives/parses only data it needs (see my question above) - if necessary, combine such optimized queries into bigger "logical" queries (utilizing callback mechanism) > (maybe asking for entity with fewer details), - all it address is a capacity > of the data being send. Not only that, capacity of data sent goes proportionally with time needed to parse & process such data on client. (Imagine big XML marshalling on client. This is why everyone prefers JSON nowadays, JSON naturally maps to native JavaScript structures with minimal computational overhead.) > > > > > michael? > > > >> > >>> > >>> Good luck, > >>> Itamar > >>> > > > > > -- > > Michael Pasternak > RedHat, ENG-Virtualization R&D > _______________________________________________ Engine-devel mailing list Engine-devel@ovirt.org http://lists.ovirt.org/mailman/listinfo/engine-devel
