A dotnet-core console application that can be used in a Docker container to pick up messages from RabbitMQ.
- The queue is provided by RabbitMQ.
- The client library to RabbitMQ is EasyNetQ.
- Docker containers isolate the different parts.
Run RabbitMQ with the management plugin in a Docker container:
$ docker run -d -p 15672:15672 -p 5672:5672 -h subscriber-rabbit --name subscriber-rabbit rabbitmq:3-management
With Docker Toolbox there're a few differences.
Set docker.local as an entry in a HOSTS file that points to the Docker
Machine IP [1]. The IP is listed when you run
docker-machine env. Now log in to http://docker.local:15672/
(default: guest/guest).
After restoring all the packages and building all the projects the following steps will create and run the container for the subscriber:
$ dotnet publish .\src\Unsettling.Dequeue\ -c debug
$ docker-compose -f .\docker-compose.development.yml build
$ docker run -d unsettling/dequeue:development
Now if you log into your local RabbitMQ you will see activity on a queue when you publish a message.
$ dotnet .\src\Unsettling.Enqueue\bin\Debug\netcoreapp1.1\Unsettling.Enqueue.dll
The queue URIs are hard-coded to keep the code size down. The docker.local
refers to an entry in a HOSTS file that points to the Docker Machine IP but the
subscriber requires the IP as it doesn't have access to the HOSTS file.
Note: Watch out for the case-sensitive Dockerfile not recognising the Debug
directory. You can just rename the folder on the filesystem to debug.
Traditionally a console application keep-alive could be managed with a single
Console.Readline() but this won't work with dotnet-core in a Windows Service,
where the original Windows-centric APIs are no longer available, or a Docker
container, where the STDIN redirection wouldn't work.
The answer is to host the console application. An easily accessible solution
lies in using the ASP.NET Core Host. We set this up in our application's
Main() method and it builds whatever is defined in the Startup class.
Now host.Run() will run the Start() method from our implementation of
IServer (in the Application class).
Startup.cs does the normal configuration of the application that you'd expect in a dotnet core application. In this example code I've foregone config to minimise the code you have to read.
IServer defines a Start method in Application.cs. It's setting up
a consumer for a single message type on a named queue in RabbitMQ. A
handler is defined: a delegate that will do something when that message is put
on the queue. The code here is massively simplified by the syntatic sugar of
EasyNetQ which provides an easy .NET API for RabbitMQ.
[1] Docker for Windows: Communication between linux and windows containers