.NET Core Microservices using GeekseatBus

GeekseatBus is a simple message bus that can be use to create microservices in .NET.

Here’s the background why we do this on our own.

Background

A lot of microservices right now is in favour using REST API for communication between services. We are in geekseat take different approach for microservices and we avoid request response between services. This is align with SOA tenets for autonomous component. You component can’t be autonomous if you still using request response. If one service dies, other service is dies too. This will create temporal coupling between services.

We are a big fan of Udi Dahan style of microservices. As it enable high cohesion and loose couple on our big system. If you want to learn more you can register for 2 days course for free from here.

The central things from this approach is the needs of message bus. Message bus is used to communicate via fire and forget and also publish and subscribe between each services. So it promotes loosely coupling between each component.

Geekseat has been researching for simple message bus on RabbitMQ. We found NServiceBus and,  Mass Transit. But both of platform can’t be used in Linux. That’s a big problem for us as our backend currently written on .NET Core ( cross platform .net ). So we decide to create our own implementation of Message Bus on top of RabbitMQ.

We has published GeekseatBus to nuget. This is a big first start for us as we are start to open source our infrastructure for microservices.
We are a great believer of keeping thing simple and minimal configuration. As an agile company we like to see our simple stuff works in production. GeekseatBus also rely on convention over configuration. This will made things easier to use.

Getting Started

Ok, Let’s get started. Here’s the schema of what we are going to achieve on this head first with GeekseatBus.

From the above schema we can see that we have 2 services. Order Service and Billing Service. Order Service have 2 component which is Order Client and Order Service ( Server ).

Geekseat.BillingService subscribe to the OrderPlaced event published from OrderService and do it’s own thing by billing the customer according to the product ordered.

Fire and Forget Demo

Now let’s open our beloved Visual Studio IDE.

Create Solution and the .NET core console application for OrderService. This will be OrderService endpoint. This service will handle PlaceOrder command and publish OrderPlaced event.

Add reference to GeekseatBus nuget package to Geekseat.OrderService project.

Create class library project for messages. We have 2 messages, PlaceOrder command and OrderPlaced event. We have convention for naming the project. You should have project name that contain service name as prefix. Ex: If your service name is Geekseat.OrderService than your message project should be Geekseat.OrderService.Messages.

You also should have create two directory for events and commands like this one. This will give you the namespace for events ( Geekseat.OrderService.Messages.Events ) and for commands ( Geekseat.OrderService.Messages.Commands)

Create PlaceOrder command on Commands folder and OrderPlaced events on Events folder. And Delete Class1.cs.

Make the content of PlaceOrder.cs like this.

And the content of OrderPlaced.cs like this.

Please make sure that your namespace follow the conventions we mention above.

Create another endpoint for Geekseat.OrderClient.

Add GeekseatBus reference to Geekseat.OrderClient. Also add GeekseatBus.OrderService.Messages to OrderClient and OrderService.

Now we can start creating a message handler for PlaceOrder in OrderService.

On Program.cs ( in OrderService ) you should start the bus with this code. Really simple startup right ?

You can try to run the OrderService to see what convention is used on creating queue and exchange in rabbitmq. Basically each service will have it’s own queue ( single queue for handling multiple message). This queue can be bind to event that the service interested in.

A service can also create an exchange for the event it’s published. You can check that OrderService have a queue named Geekseat.OrderService and Exchange Geekseat.OrderService.Messages.Events.OrderPlaced.

Let’s now send some message to our service. Now we will concentrate on Geekseat.OrderClient.

Run both OrderService and OrderClient. And press enter to send the message from Client.

Voila, it receive the message !

Publish and Subscribe Demo

Now we will publish an OrderPlaced event from OrderService. The publishing will be handle in PlaceOrderHandler. We will inject IGsBus into this handler and do publishing.

Ok. Now let’s create subscriber for that event. We will leverage exchange in RabbitMQ. But of course this will be transparent from the user.

Create a new console project Geekseat.BillingService. Add reference to messages and GeekseatBus. Create message handler OrderPlacedHandler.

Add the service startup for BillingService and we’re done.

Run all the console application (OrderService, BillingService and OrderClient). Enter the message from OrderClient and you can see that the event has been published to BillingService.

It Works !

We have open source this library on Github. You can download, experiment and give a pull request !

Happy Microservicing 🙂

 

Cheers

 

 

 

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Reading NSB Message Content

Jika terjadi exception pada handler dari NServiceBus maka proses tersebut akan di eksekusi sebanyak 5 kali secara default. Dan jika tidak juga berhasil ditangani maka message tersebut akan dipindahkan ke error queue. Kemudian exception yg ada tersebut akan di log oleh log4net.

Sehingga system administrator akan membaca log tersebut untuk mengetahui penanganan kesalahan dan setelah perbaikan mengembalikan message yg ada di error queue tersebut ke queue semula.

Penanganan tersebut dijelaskan pada Dokumentasi NServiceBus pada bagian http://www.nservicebus.com/Documentation.aspx

Innermost Exception

seringkali exception yg kita tangkap tidak benar2 bisa menjelaskan apa yg harus dilakukan untuk mengatasi masalah tersebut. Karena pesan error yg dikeluarkan tidak jelas.

Saya melihat implementasi NServiceBus dimana exception yg di log oleh log4net jelas sekali tujuannya. Exception yg diambil adalah pesan yg terdalam dari exception tersebut.

Code dari NSB tersebut saya jadikan sebagai extensions method untuk Exception.

public static class ExceptionExtensions
    {
        public static Exception GetInnermostException(this Exception e)
        {
            var result = e;
            while (result.InnerException != null)
                result = result.InnerException;

            return result;
        }
    }

Messaging via Internet

Messaging merupakan metode untuk pertukaran informasi yg cocok untuk perusahaan pusat dan cabang. Sayangnya NServiceBus tidak support untuk transport lewat internet. Trus gimana kelanjutannya teknik apakah yg akhirnya dipakai untuk mengatasi kekurangan tersebut.

Akhirnya ketemu hal yg bagus juga di blog masternya java indonesia. Mas Endy keren banget jelasin nya di sini

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NServiceBus vs WCF

Disadur dari NServiceBus Homepage

NServiceBus merupakan open source software yang dibuat oleh Udi Dahan (SOA expert). Tujuan si pembuat tentu saja untuk menjadikan NServiceBus sebagai alat yg membuat pembangunan aplikasi berorientasi service menjadi lebih mudah.

NServiceBus (NSB) dirancang untuk kolaborasi antar business-oriented services. NSB tidak bermaksud untuk menggantikan teknologi RPC seperti WCF. WCF tentu saja memiliki tempat pada arsitektur SOA tidak mungkin hanya menggunakan NServiceBus saja.

Nah NSB bukan merupakan service bus yg terpusat seperti BizTalk. Jadi NSB bukan terletak di tengah dimana komunikasi melalui central tersebut. Centralized communication seperti itu merupakan tanggung jawab dari Broker bukan Bus. Bus bukan tidak terlihat secara fisik. NSB lebih dekat ke WCF daripada ke BizTalk