On a previous post
we introduced MassTransit on this blog and presented and some reasons why it may be a real nice alternative to your system. Today we will review a simple use case: I will simulate a client/server architecture by building two console applications using
MassTransit as the service bus,
RabbitMQ as the transport running on
Docker,
.NET Core.
Sounds complicated? Let's take a look.
Installing RabbitMQ
The quickest way to install
RabbitMQ locally is by using
RabbitMQ's official Docker image. Assuming you have
docker installed on your machine, pulling and running it is as simple as:
$ docker run --hostname rmqhost --name rmqcontainer -p 15672:15672 -p 5672:5672 rabbitmq:3.7.5-management
Before running that command, let's examine what each part means:
- --hostname rmqhost : sets the host name
- --name rmqcontainer : sets the name of the container
- -p 15672:15672 : maps container port 15672 to host port 15672 so you can access on your localhost
- -p 5672:5672 : maps container port 5672 to host port 5672 so you can access on your localhost
- rabbitmq:3.7.5-management : the name of the image to donwload and run. I chose that one because it has a nice UI to manage RabbitMQ in case you want to play with it.
If you don't have that image yet, Docker will pull it for you and initialize a container based on the parameters above.
Once the download is complete, Docker will init RabbitMQ for us. On
my Fedora box, I get:
With your image loaded and you can then access the Management UI on
http://localhost:15672. Login with guest | guest:
Cool. Now that we have RabbitMQ running, let's take a look at MassTransit.
Building a shared .NET POCO Contract
Since we're building a client and a server, we also need to build a shared contract they can access. Because the client and the server may (and should) run on different servers, the common solution is to build a class library and reference it on both projects.
In .NET Core we simply type in the terminal:
dotnet new console -n MassTransit.RabbitMQ.Contracts
Then open that project and add this simple message:
That's it. Build that project to validate everything is ok and let's move to the client.
Building a MassTransit RabbitMQ Client
As previously said, the client will need to do two important things:
- connect to the bus so it can start sending messages
- send messages that the server recognizes. That's why we created the contract on the step above.
You can initialize your client with a command similar to the one executed above. Once you have your project created, the important bits are: adding a reference to the contract project previously created, initializing the bus and publishing a message to RabbitMQ.
Initializing the bus
To initialize the bus, write a code similar to:
Publishing a message
Now, we should be able to publish a message with a code like:
Build this project with $ dotnet build to make sure everything is ok but don't run it yet. We still need to build the server.
Building a MassTransit RabbitMQ Server
The simple server is pretty similar to the client with the difference that:
- the server does not publish messages
- the server contains handlers (consumers) to messages published
Build a new console app and reference the contract project created above. The gist below shows how to init a service that will run on a console terminal and handle the CreateAccount message:
Testing
Now, let's test both the client and the server to see if they're working ok. Don't forget that now you'll need your RabbitMQ instance running. I suggest running the apps side by side and let's see how that goes:
My Client App:
My Server App:
And my RabbitMQ console:
So, from the above, you see that the messages sent from the client are reaching the server. Remember, those applications do not know about each other and the only coupling between them is the standalone contract project that both references.
Conclusion
With all that we reach the end of this post. I hope this demo showed how simple it is to create a MassTransit client/server application using RabbitMQ, .NET Core. I've been using MassTransit for a couple of years now and definitely would recommend it as a base framework for your distributed systems. Want to learn more about MassTransit? Please consider reading the following posts:
Source Code
The source code used on this post
is available on GitHub.
See Also
