I work on tools build OSGi-based microservices for the likes of K8S. By extension this includes thinking/experimenting to discover whether/how OSGi is applicable in these environments.
One thing I noticed is that when you have a distributed application all of its pieces must coordinate their internal lifecycles across the network. This is more in the realm of communication between the microservices, rather than in the realm of deploying containers. For example K8S can maintain replicas of your containers, but this is for scalability rather than to create the illusion network calls can’t fail. The application running on top is expected to adapt on the fly. You really need good programming models. OSGi provides one elegant programming model. You already have services that coordinate their independent dynamic lifecycles. If you model an external entity as a service (e.g. a remote client object) you can hook your application internal state directly to it. Then use discovery to distribute knowledge when things are coming/going/relocating and have the distributed system keep itself in balance while K8S takes care of responding to load – it is a good fit. The other thing I have noticed is the inclination to think of microservices as a universal modularity solution. People brag about having hundreds of services with some consisting of one function. To share this one piece of code you seem to pay the cost of handling distribution, memory/cpu/network to maintain extra processes. This ultimately translates to paying raw money. While Martin Fawler promotes modularity through microservices he explicitly does not say where to stop if I remember correctly. Others say you need to distribute based on your business domains, not on the low level need to share some code. So microservice modularity runs orthogonally to in-process modularity. Indeed you need efficient in-process modularity to build good microservces. Here again OSGi can be a compelling solution since it tends to build really small footprint images, because it has deep understanding what each jar needs. This does not come for free – you need to describe your code well in the module metadata. The third thing I noticed is that it only really works well when you use simple/light OSGi components. Use http whiteboard, not web bundles. Use declarative services, not blueprint. And so on. Even if you use “traditional” distribution without the dynamic lifecycle it is still quite fun and OSGi has a lot to offer (e.g. JAX-RS whiteboard). So in general if you choose a microservice architecture and choose to build immutable small containers you are not at odds with OSGi. It actually can help. If you already have an OSGi application you can consider it a head start. You will have to refactor a lot to split your business logic into independent services, but you won’t refactor less if you were not OSGi based. Mohamed however mentioned he’d like to use ready-made solutions to implement application features and has issues with OSGi in that respect. What are they? OSGi can provide means to structure distributed applications, but it sure can’t provide an independent analog of every heavy-lifting framework out there. ----------------------------------- Todor Boev OSGi Platform Software AG From: osgi-dev-boun...@mail.osgi.org [mailto:osgi-dev-boun...@mail.osgi.org] On Behalf Of Jurgen Albert via osgi-dev Sent: Friday, May 3, 2019 3:41 PM To: SMAIL LOUNES; OSGi Developer Mail List Subject: Re: [osgi-dev] Migrating from OSGI to Microservices Well, like I said: Kubernetes only knows and cares about Containers (Pods) and nothing about any application life cycle. You can define e.g. dependencies like an application container requires a container with a DB. So when someone triggers the start of your application container it will make sure that the DB container is started and as far as I remember will set the coordinates to the DB as system properties for you. However, It will not know the state of readyness of your application or the DB. As an example, we have search server tailor maid for one of our customers. On first start it rebuilds the index from the raw data in their DB. This can take a couple of minutes. For Kubernetes the container is up and running, but the server will not be available to answer queries until the index is ready. Thus, if you want to use the Kubernetes API to start a Pod for a specific services it you can do that, but everything else is not in its scope. It is just a convenient tool to manage an Infrastructure. The rest belongs to your application domain. Regards, Jürgen. Am 03/05/2019 um 14:16 schrieb SMAIL LOUNES: Thank you for this remarkable answer, I'm working on a research project about developping a highly distributed and dynamic communication platform, so we're looknig for using kubernetes to manage µservices life cycle, osgi is a condidate too. we can use an osgi container to deploy some µservices.. do you have an idea about using kubernetes for life cycle mangement and how integrate it's API Thank you so much, Best regards Le ven. 3 mai 2019 à 12:25, Jürgen Albert via osgi-dev <osgi-dev@mail.osgi.org<mailto:osgi-dev@mail.osgi.org>> a écrit : Hi Mohamed, I had the fortune and in parts misfortune of being part of a few such migration projects. Besides our own internal one, everyone decided against OSGi. The descension was always because of personal resentment and/or because everybody had his personal favourite toy they wanted to play with. The reasons ranged from " We don't want to use Eclipse" (enroute with maven wasn't available at the time) over "We want spring because we don't understand OSGi and it seems to complicated" to " Java is outdated, we want to build it with NodeJS". They all jumped on the Martin Fowler approach without really considering what it means in the end. Each ended in disaster or went through a hard phase of near disaster with jobs and reputations on the line. Most ended up with something OSGiish with a lot of the pain going along with modularity but missing most of its benefits. The issue is complex but we Identified one main reason: Modularity is an abstract concept for many developers. Spring for example does not really teach and force a developer to think in a modular fashion. All I saw was a bunch of smaller Monoliths packed in Docker containers. The dynamic nature of a Microservice environment OSGi addresses with its Bundle and Service life cycle , was pushed in the realm of Kubernetes. But Kubernetes (or comparable Systems) is made for managing your Containers and not for any application and service life cycle. Thus one needs at least a few Developers/Architects that have modularity internalised and address issues early on. Another issue with the Martin Fowler approach you have already addressed. A fully distributed system comes with a lot of different problems (e.g. caches). Also the point of network latency and the time serialization and deserialization is an underestimated issue. Like Neil stated: If you are already have an OSGi application you already have a microservice architecture, but maybe no distributed one. The way to go is build a good microservice monolith (or modulith, like it is called nowadays) and then move only the services to there own containers, that really need scaling. Graham Charters talk from the 2016 EclipseCon Europe addresses this quite nicely: https://de.slideshare.net/mfrancis/microservices-osgi-better-together-graham-charters By your mention of blueprint, I deduct that you might use an older version of OSGi. Our internal project was somewhat similar and we managed to go distributed without major problems. We migrated to the latest OSGi Version and used bnd instead of PDE. Later we moved some service to there own container. It worked like charm. We could even show the process to a customer, with zero downtime, by pulling up the new containers and removing bundles with the local service implementations while the system was running. Regarding your point of finding/keep OSGi developers: This is something we are confronted with rather often. The best way get developers sold on OSGi is using the latest version of it together with bnd (pure or with the maven integration). The development speed you can reach and maintain even in complex applications makes most other Java developers jealous and interested to learn more. Regards, Jürgen. Am 03/05/2019 um 10:57 schrieb Mohamed AFIF via osgi-dev: Hi Andrei, My question had as aim to collect some experiences of suchs migrations if this exist, we're in brainstorming phase and I'm not making any judgement value about OSGI or microservices architecture, but what we push to believe that we should probely move toward another technology, is: the business requirement, indeed we want to expose our service to clients as API, and the several technical complications we 've ve been faced to everytime we want to implement a feature easily provided and could be implemented by other open framework in the market, there is also the Human ressource question is involved beacause it's not easy find/keep OSGI developers. personaly I think that OSGI is a perfect tehcnology for servers or embedded system, but I've some doubt when it's regarding applications with open architectures, it's my own view and I could be wrong Regards Mohamed. [https://ssl.gstatic.com/ui/v1/icons/mail/images/cleardot.gif] @Neil Obviously a simple Le jeu. 2 mai 2019 à 16:52, Andrei Dulvac <dul...@apache.org<mailto:dul...@apache.org>> a écrit : Hi Mohamed, Neil. Neil, while I agree with you, I think Mohamed means it in the more "modern", widely-accepted sense: https://martinfowler.com/articles/microservices.html """ In short, the microservice architectural style [1]<https://martinfowler.com/articles/microservices.html#footnote-etymology> is an approach to developing a single application as a suite of small services, each running in its own process and communicating with lightweight mechanisms, often an HTTP resource API. """ Mohamed, I'm curious what you end up with. Without getting too much into it, I dismissed the idea as something "not worth it". - Andrei On Thu, May 2, 2019 at 12:37 PM Neil Bartlett via osgi-dev <osgi-dev@mail.osgi.org<mailto:osgi-dev@mail.osgi.org>> wrote: Well the good news is that OSGi is already a microservice architecture, so you have already finished. Congratulations! If that answer doesn't quite satisfy you, maybe you'd like to describe in more detail what you are attempting to achieve and why? Regards, Neil On Thu, 2 May 2019 at 11:06, Mohamed AFIF via osgi-dev <osgi-dev@mail.osgi.org<mailto:osgi-dev@mail.osgi.org>> wrote: Hello everybody, We 're starting to study the possibility to transform our architcteure in order to migrate from OSGI to microservice architecture, and I would like to know if there is alreay some people who had thought about this subject or already start this migration. Because at first sight it would not be an easy task, many problems/issues we will be facing to them (blueprint injections, managing ditrubued caches instead of one cache in one JVM...) Many thanks -- Cdt Mohamed AFIF _______________________________________________ OSGi Developer Mail List osgi-dev@mail.osgi.org<mailto:osgi-dev@mail.osgi.org> https://mail.osgi.org/mailman/listinfo/osgi-dev _______________________________________________ OSGi Developer Mail List osgi-dev@mail.osgi.org<mailto:osgi-dev@mail.osgi.org> https://mail.osgi.org/mailman/listinfo/osgi-dev -- Cdt Mohamed AFIF _______________________________________________ OSGi Developer Mail List osgi-dev@mail.osgi.org<mailto:osgi-dev@mail.osgi.org> https://mail.osgi.org/mailman/listinfo/osgi-dev -- Jürgen Albert Geschäftsführer Data In Motion Consulting GmbH Kahlaische Str. 4 07745 Jena Mobil: 0157-72521634 E-Mail: j.alb...@datainmotion.de<mailto:j.alb...@datainmotion.de> Web: www.datainmotion.de<http://www.datainmotion.de> XING: https://www.xing.com/profile/Juergen_Albert5 Rechtliches Jena HBR 513025 _______________________________________________ OSGi Developer Mail List osgi-dev@mail.osgi.org<mailto:osgi-dev@mail.osgi.org> https://mail.osgi.org/mailman/listinfo/osgi-dev -- -- Jürgen Albert Geschäftsführer Data In Motion Consulting GmbH Kahlaische Str. 4 07745 Jena Mobil: 0157-72521634 E-Mail: j.alb...@datainmotion.de<mailto:j.alb...@datainmotion.de> Web: www.datainmotion.de<http://www.datainmotion.de> XING: https://www.xing.com/profile/Juergen_Albert5 Rechtliches Jena HBR 513025
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