Hi Folks,Update: ECF has recently completed initial documentation for 9 distribution providers [1]. We've also recently had our 3.11.0 release [2], which includes a new API for registering custom distribution providers via the whiteboard pattern.
Scott[1] http://eclipseecf.blogspot.com/2015/10/ecf-remote-services-distribution.html [2] http://eclipseecf.blogspot.com/2015/09/ecf-3110-custom-remote-services.html
On 6/3/2015 10:03 AM, Scott Lewis wrote:
On 6/3/2015 2:25 AM, Bruce Jackson wrote:I’ve now built 2 different systems based on OSGi at scale (over 1M end devices) where the endpoints needed to communicate together. In both cases, it has required some ‘server’ infrastructure to help with message passing between endpoints, but that could be a side effect of the infrastructure we had to use. However, these server components were again based on OSGi.The http question (I.e. using the HTTP service) is actually a bit of a red herring: there is nothing stopping each endpoint implementing an http service and also being a client of other endpoints to pass messages. My suggestion would be to use this approach, as it has so many side benefits, including:* good availability of tools such as Jackson for message serialisation* open protocols that will allow for different endpoint implementations in future * (by and large) avoiding problems that custom socket protocols will run into with firewall tunnelling etc…the list here is pretty long.I would like to discuss the Remote Service specification before returning to discussing protocols and RS implementations.The specification explicitly allows the runtime selection of a distribution provider to be used to export a remote service, via a standardized service property called the 'config type' (property name: service.exported.configs). As an example, the 'ecf.generic.server' distribution provider is the config type used in this tutorial [1].I feel that one of the most useful aspects of the config type and the underlying distribution system is that it abstracts away the implementation specifics, i.e. the transport protocol (e.g. http, jms, tcp, mqtt, private, etc), as well as the serialization mechanism/format (json, binary, xml, etc). It does this for both the remote service creator/implementer and for the remote service consumer.IMHO, there are there are many advantages of doing this. A big one is modularity and reuse. Why should it be necessary for every remote service author to implement a brand new protocol and serialization, in order to remote their micro service? Another one is flexibility: any given reasonably sophisticated app has changing requirements over time, and sometimes these changing requirements require flexibility in the underlying libraries. Another big advantage is getting access to all the simplicity, dynamics, versioning, and other capabilities of OSGi services provided by the OSGi service registry and libs built on top of it (e.g. DS, etc). There are of course many others.Of course, there are disadvantages in reusing distribution systems or any set of libraries: Perhaps the protocol or serialization mechanism that's widely implemented and popular today doesn't meet your application's performance needs. Perhaps there are more appropriate or new protocols, or improved implementations. Perhaps you have unique security requirements. Perhaps you have timing or reliability requirements that are difficult to address. There are lots of application-specific reasons for favoring or disfavoring non-functional requirements like performance, ease of deployment and management, security (e.g. firewalls), network reliability/failure handling, etc.But in my view, the Remote Services specification adopts a nice balance here, by allowing potentially many distribution providers, down to the level of the individual service instance set at *service instance registration time*. Even if one needs to create a new, entire distribution system, there are still many advantages of using OSGI Remote Services...e.g. the service registry's graceful handling of dynamics inherent in a network-based service, versioning, discovery, and the ability for service creators and perhaps more importantly service consumers to ignore some of the subtle and difficult aspects of distribution (e.g. partial failure, timing, etc). I do think that standardizing these advantages and having many implementations will over time make it easier to build, use, understand, and manage distributed applications.Returning to RS implementations: The approach ECF has taken (since well before the Distributed OSGi rfc and RS/RSA standardization) has been protocol neutral. As such we have gone to the trouble of creating extensible APIs for various types of network communication: e.g. filetransfer, instant messaging, group messaging, voice over ip, network service discovery, and remote services distribution (of course). For each of these types, we have multiple protocol implementations, some created by us (in open source), some created by others (in open source or not). This is true, of course, for our OSGi Remote Services implementation, and it's distribution and discovery subsystems...as I've said we have a number of providers that are based upon tcp and we have providers that are based upon http and REST. But more importantly (I think), we are trying to support the creation of hopefully many other/new providers, created by others...possibly extending those that already exist...that meet their needs for app-specific non-functional requirements, new/popular application areas (like IoT) for distributed applications.The way that we do this with a multi-provider/multi-protocol approach is to:0) Fully implement the latest specs an test for compliance1) Define stable, extensible, open APIs for distribution and discovery (e.g. 'remote services api' -> distribution, 'discovery api' -> discovery), and maintain/enhance these APIs. 2) Re-use existing work to create stable, extensible, open provider implementations for these types (e.g. ecf generic, http/REST, r-osgi, jms, mqtt, etc) 3) Do what we can in open cooperation with the community to document and provide examples for both 1 and 2, as well as document how to create new providers [2], and analyze the runtime characteristics of existing providers. 4) Engage the community (commercial and open source) to drive 0-3 forword in the directions that are most needed, and get support for these efforts via new committers, contributors, collaborators, and supporters [3].5) Provide the support for the community in doing all of the aboveAre we resource-limited? Yes, unless you consider the community. Is there more to do? (particularly around documenting individual providers)? Yes. My comment is that in today's software world I don't think these answers are particularly uncommon ;-). [4]Scott[1] https://wiki.eclipse.org/Tutorial:_Building_your_first_OSGi_Remote_ServiceSee section: Service Host: Register and Export the Service[2] https://wiki.eclipse.org/Tutorial:_Creating_a_RESTful_Remote_Service_Provider[3] https://projects.eclipse.org/projects/rt.ecf/who [4] https://www.eclipse.org/ecf/NewAndNoteworthy_3.10.0.htmlOn 02/06/2015 16:08, "Scott Lewis" <sle...@composent.com> wrote:*** DISCLAIMER *** This message, including attachments, is intended solely for the addressee indicated in this message and is strictly confidential or otherwise privileged. 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Opinions, conclusions and other information expressed in this message are not given or endorsed by Myriad Group AG unless otherwise indicated by an authorized representative independent of this message.On 6/2/2015 2:16 AM, Simon Kitching wrote:Hi Scott, Maybe I shouldn't hijack a thread on the Felix list to ask about ECF, but we are already talking about remote-services implementations, and you are here so I'll do it :-) Link [1] has instructions on using ECF's remote services on Karaf which lead to this karaf features file: http://download.eclipse.org/rt/ecf/3.8.0/site.p2/karaf-features.xml. That file appears to indicate that 49 bundles are needed (the majority from eclipse.org). Plus bundles to support whatever discovery provider is desired. That doesn't seem reasonable; other remote-services implementations have 1-3 bundles. Have I understood correctly?For the latest the correct URL is: http://download.eclipse.org/rt/ecf/latest/site.p2/karaf-features.xml ECF's implementation is quite modular, and so is made up of more bundles, generally much smaller and finer-grained.<stuff deleted> Looking at the commit-log for the osgi code, I see that you are the only committer since at least the start of 2014. Is this correct?I have done the majority of the commits from the start of 2014, but am not the only committer. The source code history is not a very good indicator of overall contributions for a project in this point in it'slife-cycle. Also, much of the recent coding work on ECF (by myself andothers) has taken place on our github repos[4].<stuff deleted> Regarding building from source : I see no Maven, Ant, Groovy or bnd buildfiles in the sourcecode - just eclipse project files. Could you point me to instructions on how to build artifacts from the source-code (ideally outside of the Eclipse IDE)?We currently use Eclipse + buckminster to build, and are part of the Eclipse Simultaneous Release (which also uses buckminster). There are contributors from Red Hat that are working adding to use Tycho to build. FWIW, we also produce a maven repos as part of our build [A].And is there any easy way of seeing what the dependencies of the projects under osgi/bundles are (the kind of info visible in a maven pom-file)?From Eclipse, certainly. When Red Hat's contribution is in place you will be able to do with maven-pom file as well.Is there a list of the implemented "distribution providers" (network protocols for the actual remote method invocation) available, with details on the features and performance of each choice?No, regrettably we don't have that. I've opened an enhancement request to that effect [B]. There was some performance analysis work contributed some time ago, but unfortunately I think it's likely pretty obsolete by now.I couldn't find one. In particular, I needed a high-performance protocol - one that (a) keeps network sockets open rather than opening a new connection for each call, and (b) uses a high-performance serialization mechanism, ie not xml. I couldn't find any page with that kind of information in it. The closest I found was: *https://wiki.eclipse.org/Discovery_and_Distribution_Provider_Configuration_Options*https://wiki.eclipse.org/Comparison_of_Discovery_and_Distribution_Providersbut neither of those pages are very useful. In particular, "r-osgi" and "ecf generic" are not described in any way.For the details about everything there's always 'use the source'. :-) I can tell you that r-osgi, ecf generic, JMS, MQTT distribution providers all 1) keep network sockets open as you describe; 2) use java object serialization as the default I can also tell you that all of those providers, and the distribution API that they implement (known to us as the 'remote services api'), arecustomizable/extensible for both 1 and 2...meaning that if you wish, you can replace both the serialization as well as the socket-level transportwith something more suitable for your use case without having to implement a distribution provider from scratch. As a an example, that is how websockets support was added in the 3.10 release cycle. I propose moving this to ecf-dev or direct correspondence if you want more details. Scott [A] http://build.ecf-project.org/maven/ [B] https://bugs.eclipse.org/bugs/show_bug.cgi?id=469155 --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@felix.apache.org For additional commands, e-mail: users-h...@felix.apache.org--------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@felix.apache.org For additional commands, e-mail: users-h...@felix.apache.org--------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@felix.apache.org For additional commands, e-mail: users-h...@felix.apache.org
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