This is a great and coherent answer and it made me think a lot. > Others say you need to distribute based on your business domains, not on the low level need to share some code.
But neither choice has an impact on the size of the (micro-) service > So microservice modularity runs orthogonally to in-process modularity. Indeed you need efficient in-process modularity to build good microservces. What I meant when I said there's an overlap it's the modularisation part. Yes, with OSGi you can and might want to modularise your service further, but if you're going through the infra and ops cost of maintaining and deploying microservices, you can split down a larger service further into two microservices (if performance and the arch permits). And if your services are quite split already, how much benefits do the extra in-process modularisation bring you? Don't get me wrong, I love OSGi and, on top of that, I think it's actually a better way to start a project from a green field and make use of that modularisation. So start with a monolith in that strict sense (as you don't have the scalability part). And when you need all the advantages of microservices in the strict sense, your service is already modular (*) and you can just take out the part that needs to scale and make it a separate service that you can scale independently. A wise man once told me: "You will never get the architecture and domain boundaries right from the start with microservices" (*) As long as you future-proof a bit and don't make an architecture that assumes blindly that osgi services are sharing the process with other services. - Andrei On Fri, May 3, 2019 at 5:32 PM Boev, Todor via osgi-dev < osgi-dev@mail.osgi.org> wrote: > 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> 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. > > > > > > > > > > > > > > > > @Neil > > Obviously a simple > > > > > > > > Le jeu. 2 mai 2019 à 16:52, Andrei Dulvac <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> 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> 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 > https://mail.osgi.org/mailman/listinfo/osgi-dev > > _______________________________________________ > OSGi Developer Mail List > 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 > > 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 > > Web: www.datainmotion.de > > > > XING: https://www.xing.com/profile/Juergen_Albert5 > > > > Rechtliches > > > > Jena HBR 513025 > > _______________________________________________ > OSGi Developer Mail List > 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 > > Web: www.datainmotion.de > > > > XING: https://www.xing.com/profile/Juergen_Albert5 > > > > Rechtliches > > > > Jena HBR 513025 > > _______________________________________________ > OSGi Developer Mail List > osgi-dev@mail.osgi.org > https://mail.osgi.org/mailman/listinfo/osgi-dev
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