How to share database connection between in spring cloud

Question

How can I share database connection aong in spring cloud module microservices. If there are many microservices how can i use same db connection or should i use db connection per microservices?

Answer 1

In my opinion, the thing that you've asked for is impossible only because each microservice is a dedicated process and it runs inside its own JVM (probably in more than one server). When you create a connection to the database (assuming you use connection pool) its always at the level of a single JVM.

I understand that the chances are that you meant something different but I had to put it on because it directly answers your question

Now, you can share the same database between microservices (the same schema, tables, etc) so that each JVM will have a set of connections opened (in accordance with connection pool definitions). However, this is a really bad practice - you don't want to share the databases between microservice. The reason is the cost of change: if you (as a maintainer of microservice A) decide to, say, alter one of the tables, now all microservices will have to support this, and this is not a trivial thing to do.

So, a better approach is to have a service that has a "sole responsibility" for your data in some domain. Now, all the services could contact this service and ask for the required data through well-established APIs that should never be broken. In this approach, the cost of change is much "cheaper" since only this "data service" should be changed in a way that it doesn't break existing APIs.

Now regarding the database connection thing: you usually will have more than one JVM that runs the same microservice (like data microservice) so, it's not that you share connections between them, but rather you share the same way of working with database (because after all its the same code).

Answer 2

When dealing with a mircoservice architecture it is usually the case that you have a distributed system.

Most microservices that communicate with each other are not on the same machine, instance or container. Communication between them is most commonly done via http, though there are many other ways.

I would suggest designing mircoservices around a single concern of your application. For example, in your case, you could have a "persistence microservice" that would be responsible for dealing with data persistence operations on a single or multiple types data-stores. It could possibly deal with relational DBs, noSQL, file storage etc. Then, via REST endpoints, you can expose any persistence functionality to the mircoservices that deal with business logic.

A very easy way to build a REST service like this would be with the help of Spring Data REST project.

To answer your actual question, I'm not aware of any way to share actual connections between processes. Beyond that, having many microservices running on the same instance is not a good practice most of the time.

Mircoservices are very popular these days and everybody is trying to transition to them. My advice would be to make sure you don't "over-engineer" your project.

Hope I didn't misunderstand your question, but to be fair it is a little vague. If you could provide a longer more detailed description of your architecture and use case I can suggest more tools/frameworks you can use to achieve your cloudy goals.

Answer 3

First and most important - your microservice should be responsible for handling all data in a given business domain/bounded context. So the question is - 'Why do you need to share database connection between microservices and isn't this a sign you went too far with slicing your system?' Microservice is a tool and word 'micro' may be misleading a bit :)

For more reading I would suggest e.g. https://learn.microsoft.com/en-us/dotnet/standard/microservices-architecture/architect-microservice-container-applications/identify-microservice-domain-model-boundaries (don' t worry, it's general enough to be applicable also to Spring).