I am not against boundary, I am just against making things unnecessary complex to enable boundary. If we are going this way, I hope we can make it as much as transparent to developers. That means, as a developer, all a plugin I need to do is 1) provide my separate spring xml 2) inject beans I want (valid beans) in my bean and code business logic 3) compile to a jar and put to some place designated by CloudStack. That's it.
I raise this topic because I have seen some projects to create boundary making things horrible complex. And sometimes developers are hurt by wrong boundaries, as a result, to overcome these limitations people write lots of ugly code which makes thing even worse. However, I am still worry about if we can make things so simpler. For example, we may have an orchestration context that contains major beans needed by almost every plugin, this context can be easily set as parent context for all plugin contexts when bootstrap. However, if a plugin A needs to access some bean defined in plugin B, given they are sibling, how plugin framework resolves the dependency ? > -----Original Message----- > From: Darren Shepherd [mailto:darren.s.sheph...@gmail.com] > Sent: Wednesday, September 18, 2013 11:53 AM > To: dev@cloudstack.apache.org > Subject: Re: [PROPOSAL] Modularize Spring > > I'm not for OSGi either, but contexts are quite useful and will lead to better > things. First off, we don't want one gigantic spring XML config file like we > have > today. I think we can all agree on that. So each plugin will have to supply > its > own XML. So the obstacles you mention, will largely be just that for people. > > With Spring it is really simple to just inject dependencies and cross > architectural boundaries. Its currently everywhere in ACS. You can't just > say > we should review code and make sure nobody doesn't do bad things. A little > bit > of framework to enforce separation is a good thing. But I'm guessing you will > disagree with me there. > > Here are some random points on why contexts are good. Say I want to use > Spring AOP or Spring TX in my plugin. With your own context you can ensure > that you won't screw with anybody else code by accidentally having you > pointcut match their bean. You don't have to worry about bean name conflicts. > If two config files specify bean X, Spring will gladly just use the last one. > I've > already found multiply defined beans in ACS, but things still just happen to > work. > Having multiple contexts also defines initialization order. We can ensure > that > the framework is loaded and ready before child context are loaded and started. > (we kind of do this today with ComponentLifeCycle, but its a hack in my mind). > Additionally, when things start you will know, loading context "crapping plug > X". > If spring fails to initialize, the issue it there. Today, if spring fails to > start, it > could be one of over 500 beans causing the weird problem. The list goes on > and on. > > Finally, this is the big one and why I really want contexts. I have some > notes on > the wiki [1] that you might want to read through. Basically I want to get to > a > more flexible deployment model that allows both a single monolithic JVM as > today and also a fully distributed system. Having contexts in hierarchy will > enable me to accomplish this. By selecting which contexts are loaded at > runtime will determine what role the JVM takes on. The contexts help people > better understand how the distributed architecture will work too, when we get > there. > > Frank, trust me, I hate complex things. I don't want OSGi, classloader magic, > etc. But I do like organization and a little bit of framework so that people > don't > accidentally shoot themselves in the foot. I personally like knowing that I > couldn't have screwed something up, because the framework won't even allow > it. If we separate everything as I want today, and then tomorrow we say this > is > way too much overhead, moving to a flat context is simple. Don't think we are > on some slippery slope to classloaders and dependency hell. > > Darren > > [1] > https://cwiki.apache.org/confluence/display/CLOUDSTACK/Nothing+to+see+her > e...#Nothingtoseehere...-DeploymentModels > > > > On Wed, Sep 18, 2013 at 11:22 AM, Frank Zhang > <frank.zh...@citrix.com>wrote: > > > What's the point in using separate spring context per plugin? > > Separate class loader is the thing I hate most in OSGI, I am afraid we > > are on the same way. > > Frankly speaking, I never see benefits of this *separate* model, our > > project(or most projects) is not like Chrome which has to create > > sandbox for extensions in order to avoid bad plugin screws up the > > whole browser(however, I still see bad plugins screw up my Chrome > > well). > > Projects like CloudStack using plugin to decouple architecture should > > not introduce many isolations to plugin writer, the point preventing > > wrong use of some components is not making much sense to me. If a > > plugin not following guide(if we have > > it) we should kick it out, instead of making obstacles for 99% good people. > > > > > > > > > -----Original Message----- > > > From: Darren Shepherd [mailto:darren.s.sheph...@gmail.com] > > > Sent: Wednesday, September 18, 2013 10:33 AM > > > To: dev@cloudstack.apache.org > > > Subject: Re: [PROPOSAL] Modularize Spring > > > > > > Right, component isn't a thing. I probably shouldn't use that term. > > > I > > want to > > > standarize on the naming convention of plugin, module, and extension. > > It is > > > explained a bit on the wiki [1] but I'll try to do a little better > > > job > > here. So a > > > plugin is basically a jar. A jar contains multiple modules. A > > > modules > > ends up > > > being a spring application context that composes multiple > > > configuration > > files. > > > Modules are assembled into a hierarchy at runtime. Extensions are > > > implementations of interfaces that exist in a module. A maven > > > project produces a jar, so a plugin ends up being a maven project also. > > > > > > So currently today we don't have a strong definition of Plugin and I > > hope to > > > address that. > > > > > > Darren > > > > > > [1] > > > https://cwiki.apache.org/confluence/display/CLOUDSTACK/Plug- > > > ins%2C+Modules%2C+and+Extensions > > > > > > > > > On Wed, Sep 18, 2013 at 4:25 AM, Daan Hoogland > > > <daan.hoogl...@gmail.com>wrote: > > > > > > > sounds great Darren, > > > > > > > > By component, you mean maven project or some larger chunk like > > > > distribution package? (did i miss this definition somewhere or do > > > > we define the components now?) > > > > > > > > regards, > > > > Daan > > > > > > > > On Wed, Sep 18, 2013 at 12:10 AM, Darren Shepherd > > > > <darren.s.sheph...@gmail.com> wrote: > > > > > Currently ACS code is fairly modular in that you can add > > > > > plug-ins to ACS > > > > to > > > > > extend most functionality. Unfortunately ACS is not packaged in > > > > > a > > > > modular > > > > > way. It is still delivered essentially as one large unit. > > > > > There are > > > > many > > > > > reason for this but one large barrier to modularizing ACS is > > > > > that the Spring configuration is managed as one large unit. > > > > > > > > > > I propose that we break apart the Spring XML configuration such > > > > > that each component contributes its own configuration. > > > > > Additionally each component will be loaded into its own Spring > > > > > ApplicationContext such that its beans will not conflict with > > > > > the wiring of other beans in ACS. This change > > > > will > > > > > lay the foundation for a richer plugin model and additionally a > > > > > more distributed architecture. > > > > > > > > > > The technical details for this proposal can be found on the wiki [1]. > > > > > > > > > > Darren > > > > > > > > > > [1] > > > > https://cwiki.apache.org/confluence/display/CLOUDSTACK/Modularize+ > > > > Spri > > > > ng > > > > > >
