Running multiple Quarkus instances on one machine

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I have an application separated in various OSGI bundles which run on a single Apache Karaf instance. However, I want to migrate to a microservice framework because

  • Apache Karaf is pretty tough to set up due its dependency mechanism and
  • I want to be able to bring the application later to the cloud (AWS, GCloud, whatever)

I did some research, had a look at various frameworks and concluded that Quarkus might be the right choice due to its container-based approach, the performance and possible cloud integration opportunities.

Now, I am struggeling at one point and I didn't find a solution so far, but maybe I also might have a misunderstanding here: my plan is to migrate almost every OSGI bundle of my application into a separate microservice. In that way, I would be able to scale horizontally only the services for which this is necessary and I could also update/deploy them separately without having to restart the whole application. Thus, I assume that every service needs to run in a separate Quarkus instance. However, Quarkus does not not seem to support this out of the box?!? Instead I would need to create a separate configuration for each Quarkus instance.

Is this really the way to go? How can the services discover each other? And is there a way that a service A can communicate with a service B not only via REST calls but also use objects of classes and methods of service B incorporating a dependency to service B for service A?

Thanks a lot for any ideas on this!

quarkus microservices osgi
1 Answers

I think you are mixing some points between microservices and osgi-based applications. With microservices you usually have a independent process running each microservice which can be deployed in the same o other machines. Because of that you can scale as you said and gain benefits. But the communication model is not process to process. It has to use a different approach and its highly recommended that you use a standard integration mechanism, you can use REST, you can use Json RPC, SOAP, or queues or topics to use a event-driven communication. By this mechanisms you invoke the 'other' service operations as you do in osgi, but you are just using a different interface, instead of a local invocation you do a remote invocation.

Service discovery is something that you can do with just Virtual IP's accessing other services through a common dns name and a load balancer, or using kubernetes DNS, if you go for kubernetes as platform. You could use also a central configuration service or let each service register itself in a central registry. There are already plenty different flavours of solutions to tackle this complexity.

Also more importantly, you will have to be aware of your new complexities, but some you already have.

  • Contract versioning and design
  • Synchronous or asynchronous communication between services.
  • How to deal with security in the boundary of the services / Do i even need security in most of my services or i just need information about the user identity.
  • Increased maintenance cost and redundant side code for common features (here quarkus helps you a lot with its extensions and also you have microprofile compatibility).
  • ...

Deciding to go with microservices is not an easy decision and not one that should be taken in a single step. My recommendation is that you analyse your application domain and try to check if your design is ok to go with microservices (in terms of separation of concenrs and model cohesion) and extract small parts of your osgi platform into microservices, otherwise you mostly will be force to make changes in your service interfaces which would be more difficult to do due to the service to service contract dependency than change a method and some invocations.

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