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In my last article I mentioned that we had cases when we needed to split our back-end application across several processes and as a result we gained more flexibility when we needed to scale the application. This time I want to keep sharing some insights on why we try to keep some parts of the application loosely coupled. This time I wanted to talk about loose coupling at design time when the whole application might run in the single process. According to one of the definitions ”loosely coupled system is one in which each of its components has, or makes use of, little or no knowledge of the definitions of other separate components”. In object oriented paradigm, that we are using to create our Fitradar application, most of the code is spread among various classes and therefore the smallest component that we consider is a class. And since classes are just containers for data and functions then we usually see the loose coupling as a way how to call a function of another class with little information as possible.
The simplest way how to call a method on the other object is to create that object from a class (in Java and C# we do that by new operator) and call the needed method. But it turns out there are many cases when it is undesirable to know the class name of an object or even a specific method name during the design time and therefore there are several methods how to reduce the knowledge of a class we are going to use and a method we are going to call:
On the larger scale where components are not anymore single classes but the whole systems the loose coupling further can be achieved by introducing the middle-ware like Queues and Service Buses.
As we can see making a method call something that is not bound to a single implementation opens up a dozen of options how to design and build an application in very flexible way.
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Recently our team finished the work on FitRadar booking system. That was quite a challenging task and I decided to share some insights and knowledge we gained during the design and development of this system. Already on the early stage of designing and requirement gathering it was clear that ticket booking system on the back-end should be independent from the rest of the Fitradar system because we wanted to introduce Event Sourcing for such entities as Order and Payment. Since these two entities are responsible of money charging and money is always a very sensitive topic, we wanted to make sure we can always track down the state changes in booking and payment processes. But to what degree it should be independent was the question we had to answer.
So there is very little we can do about object decoupling at runtime in single process application case, but do we really need to deploy a booking system in a separate application? Maybe we can just isolate our booking system in a separate library and still run it in the same process with the rest of FitRadar libraries? And so we started to investigate it. Very quickly we noticed that our ideas of making booking system independent from the rest of application strongly reassembles the principles of Microservices architecture . And since now days there are a lot of talks around the Microservices we thought that our project might be a good candidate to move to Microservices architecture. But just because something is promoted doesn’t mean it fits your needs. You usually don’t start the development of application as a distributed system, unless it was a requirement from the beginning. Applications usually mature to the state when Monolithic Architecture doesn’t satisfy the initial requirements and a team starts to consider switching to Microservices Architecture. And we wanted to make sure that this is the time when the new feature requires us to switch to the new Architecture to make the development easier in the future. Here are the advantages of Microservices Architecture that really attracted our attention:
And for our project it seemed that we will gain more than loose if we will treat booking system as separate application and deploy it in a separate process. So we gave it a try.
Visit our website: http://fitradar.me/ and join the mailing list. Our app is coming soon!