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From Bishnu Gautam <bishn...@hotmail.com>
Subject RE: River-examples project - followup
Date Mon, 13 Apr 2015 00:22:17 GMT
Great explanation GreggLet's have a tutorial how a Jini service can bypass the firewall constraint
by using HTTP endpoint in Raspberry Pi.Once we have such a tutorial, I am pretty sure that
JINI/River will take lead in developing cloud/fog services.RegardsBishnu

Bishnu Prasad Gautam


> From: greggwon@gmail.com
> Subject: Re: River-examples project - followup
> Date: Sat, 11 Apr 2015 23:50:26 -0500
> To: dev@river.apache.org
> 
> The important thing for me, is to provided simple APIs.  The basics of what I am talking
about are visible in my startnow project which has been out on java.net for about 15years
now.  Some of that is rough and unfinished work.  But the basics are, I think you should be
able to start a service like
> 
> public class MyApplication extends PersistentJiniService {
> 	public static void main(string args) {
> 		new MyApplication(args).startService();
> 	}
> 
> 	public MyApplication(args) {
> 		super(args);
> 	}
> }
> 
> The implication is that everything is in your configuration, and the default configuration
should be a nice set of reasonable defaults which include things like a default port for the
services endpoint, which we should register and advertise in the well known service names
list.  That would help with firewall rule support.  For more than one service/endpoint, we
should have an automatic recognition of more than one service being started in a JVM, and
we should be able to provide the "next" port to use through a method in PersistentJiniService
which could be overridden to return different ports.
> 
> There are lots of "choices" which don't add value to the new user experience.  It would
be best to make reasonable defaults for the average user who would put a service up for testing.
> 
> The other item would be to provide a new Jeri InvocationLayerFactory and Endpoint which
would allow a single port to be used for all inbound services.  The basic idea is that the
InvocationLayerFactory construction would provide some kind of mechanism for services to be
registered and authentication and everything would just work for multiple services on the
same endpoint.
> 
> Think about how HTTP routing works in most modern HTTP services.  The user might use
Annotations or something to mark the service entry points and we would then be able to use
that information to cause the InvocationLayerFactory to call out to the correct class and
method.
> 
> We really should look at creating an HTTP endpoint with the ability to use POST as an
inbound invocation that would deliver a JSON message to the function bound to that HTTP request.
 This would allow small, lightweight restful services to be created without a large complex
web server underneath it. 
> 
> I think that this would make Jini on Raspberry Pi particularly alluring.
> 
> Gregg Wonderly
> 
> 
> > On Apr 8, 2015, at 9:12 PM, Patricia Shanahan <pats@acm.org> wrote:
> > 
> > Maybe it would be possible to put one or more of the richer functions in an example?
That would let us get practical experience before committing to an API change.
> > 
> > Patricia
> > 
> > On 4/8/2015 6:47 PM, Gregg Wonderly wrote:
> >> I think that it could be beneficial, to provide code examples, in
> >> some form that do the two different things that are possible to make
> >> this less visible.  First, show the reader how to use an exit hook in
> >> the tutorial to see the service registration disappear.  Second, show
> >> them how to use the lease timeout value to make the change happen
> >> automatically for the case of a network split or network card or
> >> computer failure that would keep the exit hook from ever generating
> >> network traffic to cancel the lease.
> >> 
> >> I still feel that we actually need new APIs that operate at a bit
> >> higher level and provide all of these things as parameters to richer
> >> functions.
> >> 
> >> Gregg Wonderly
> >> 
> >>> On Apr 6, 2015, at 8:56 PM, Greg Trasuk <trasukg@stratuscom.com>
> >>> wrote:
> >>> 
> >>> 
> >>> Hi all:
> >>> 
> >>> I updated the tutorial to include the discussion below in the
> >>> “hello-service” module.  ‘svn up’ should bring it down to your
> >>> local machine.  I haven’t yet integrated Patricia’s formatting
> >>> suggestions, mainly because I have to dig in to Maven’s site
> >>> command a bit to include the correct css, but I’ll do that before
> >>> we release.
> >>> 
> >>> Any feedback is greatly appreciated.
> >>> 
> >>> Cheers,
> >>> 
> >>> Greg Trasuk
> >>> 
> >>> On Apr 6, 2015, at 3:30 PM, Greg Trasuk <trasukg@stratuscom.com>
> >>> wrote:
> >>> 
> >>>> 
> >>>> Hi Dan:
> >>>> 
> >>>> Thanks for the great feedback.
> >>>> 
> >>>> I’m pretty sure you already know this, Dan, since you’re a
> >>>> long-time Jini user, but let me explain for the newer folks and
> >>>> the archives.  This is a case where what you’re seeing is the
> >>>> expected behaviour.  When the service registers itself with
> >>>> Reggie, it takes out a lease on the registration. That lease is
> >>>> usually renewed periodically by the service’s JoinManager (that
> >>>> isn’t quite the whole story, but it’ll do for now).  When you
> >>>> kill the service unexpectedly with ctrl-c, the service doesn’t
> >>>> de-register itself, however the lease eventually runs out (now
> >>>> that it’s not being renewed by the service) and then the
> >>>> registration expires, allowing Reggie to reclaim its resources
> >>>> and notify any registrar listeners.
> >>>> 
> >>>> It would be possible to register a vm shutdown hook to
> >>>> de-register the service before the vm exits, but in this case I
> >>>> think it’s actually better to leave it out, since it demonstrates
> >>>> nicely that a dead  service (or at least a dead JoinManager)
> >>>> eventually gets dropped from the registrar.
> >>>> 
> >>>> You said the duplicate service instances “worked”, in that you
> >>>> can show info and browse the service, but of course, you’re
> >>>> really just looking at the information that’s in the registry -
> >>>> the registrar and service browser don’t actually contact the
> >>>> service.  Reggie has no knowledge of the “liveness” of the
> >>>> service, and doesn’t attempt to do any “health check”.
> >>>> 
> >>>> In fact, it’s a common misconception that if the service renews
> >>>> the lease, it must be “live”.  This turns out to be false for
> >>>> many reasons.  (1) The service could have delegated its lease
> >>>> renewals to a different service.  (2) There’s no guarantee that
> >>>> failure of the actual service thread would also cause failure of
> >>>> the lease renewal thread, even if they are in the same process
> >>>> (embedded programmers might recognize this as being similar to
> >>>> the “resetting the watchdog in a timer-triggered interrupt
> >>>> service routine” problem).  (3) Even if there were a health check
> >>>> task, the service could fail in the instant just after the health
> >>>> check.  The most a health check, monitor or heartbeat can do is
> >>>> place a limit on how long it takes to find out a service has
> >>>> failed.  The only way to say with certainty that a service
> >>>> “works” is to attempt to use it.
> >>>> 
> >>>> The lease is purely for the convenience of the registrar (or
> >>>> generically, the service granting the lease).  If ever the lease
> >>>> is not renewed, the landlord can go ahead and reclaim whatever
> >>>> resources were dedicated to the lease.  In the case of Reggie, if
> >>>> the lease isn’t renewed, Reggie drops the registration.  So
> >>>> there’s little risk of “stuck registrations”.  And since the
> >>>> lease can be renewed, there’s no need for any kind of extended
> >>>> default timeout.
> >>>> 
> >>>> So, I think I’ll put most of the above explanation into the
> >>>> tutorial, unless anyone has other thoughts.
> >>>> 
> >>>> Cheers,
> >>>> 
> >>>> Greg Trasuk
> >>>> 
> >>>> On Apr 6, 2015, at 1:42 PM, Dan Rollo <danrollo@gmail.com>
> >>>> wrote:
> >>>> 
> >>>>> Hi Greg,
> >>>>> 
> >>>>> I finally took some time to try this out. It really looks great
> >>>>> to me!
> >>>>> 
> >>>>> I noticed one minor thing that I thought might confuse users:
> >>>>> While going through tutorial steps, I decided to stop (via
> >>>>> cntrl+c) are restart the hello-service a couple times. This
> >>>>> resulted in the service being shown multiple times in the
> >>>>> service browser (screenshot attached). It appeared all the
> >>>>> duplicate instances in the browser “worked” (I could “show
> >>>>> info” and “browse service” on all of them). Eventually, the
> >>>>> duplicate registrations “cleaned up” and I was left with just
> >>>>> one. I’m not sure how best to avoid confusion about this
> >>>>> situation. Would more doc about “why”/“how” that works just
> >>>>> complicate things? Is there any sort of “force lease check”
to
> >>>>> do in the browser that could clear up the duplicates sooner?
> >>>>> (And if so, would that be worth noting in the tutorial?). So
> >>>>> basically, not sure this is a “problem”, but thought I’d ask…
> >>>>> 
> >>>>> Thanks! Dan
> >>>>> 
> >>>>> <revier-examples-RepeatedService.png>
> >>>> 
> >>> 
> >> 
> 
 		 	   		  
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