.Net and Docker

Using Mono, we can take advantage of both linux and docker, which equals some really exciting stuff. In this post we will take a C#, .NET 4.6 and Nancy “hello world” example and run this in a docker container.

Pre-Req

for this example, the following tools are being used (replace with your tools of choice)

• VS Code or Studio - to edit source code and compile
• Docker 1.7 + (im using vagrant box-cutter/ubuntu1404-docker image)
• Docker Hub
• Servers with docker on them (I like to use Rancher, as it makes this far easier to work with)

Step 1 - code

Docker containers are designed to run a process and exit when they are complete. In our case we want a blocking application.

1. Create a normal console line application, using .NET 4.6 (for now im using full .NET), I callled it “TestMvc.Host”
2. Add a reference to NancyFX (make sure you get the latest)
3. write your code, note that when you start your host, that you block the main thread using Thread.Sleep.
4. Compile your code (you can compile using Mono or MS .NET),

static void Main(string[] args)
{
    Console.CancelKeyPress += (sender, eventArgs) =>
    {
        Console.WriteLine("exiting...");
    };

    Console.WriteLine("About to start server");
    using (var host = new NancyHost(new Uri("http://localhost:80")))
    {
        host.Start();

        Console.WriteLine("started, press \"ctrl + c\" to exit");
        Thread.Sleep(Timeout.Infinite);
    }
}

The sample Nancy Module in this test app

public class HelloModule : NancyModule
{
    public HelloModule()
    {
        Get["/"] = parameters => $"Hello from {Environment.OSVersion.Platform}";
    }
}

note: the Thread.Sleep is intensional, as it will not cause the container to exit. do not use ReadKey or ReadLine.

note 2: we are hosting our service on port 80.

Step 2 - Compiling a docker image

For this part I cheat a little and use VM setup via Vagrant using the box-cutter/ubuntu1404-docker image.

1. Create a new folder, i will call this releaseImage, this will be used to used to
2. Copy the compiled filed into the new releaseImage, all the dll’s and exe.

1. Create a file called “Dockerfile” no extension, if you do this in VS code it will supply some level of syntax support.

Dockerfile

FROM mono
COPY . /serv
CMD [ "mono",  "/serv/TestMvc.Host.exe" ]
EXPOSE 80

what we are doing here is creating a new image, which uses the “mono” as the base. We copy all the files from current folder on the HOST machine (releaseImage) into a folder called serv in the container image. it finishes off by letting docker know that a container using this image should run the TestMvc.Host.exe and expose port 80.

1. open docker command (I do this by accessing vagrant ssh), remember to run docker login,
2. cd into the releasesImage folder
3. build the image (replace dbones with your docker hub account)

docker build -t "dbones/testnet" .

1. you can confirm this by running docker images command and the new image will be listed. you may also run a container directly off the image.

Step 3 - publishing

once you have built the image, you can run it directly, or publish it, and then you can run it on another computer ( :) ), I want to do the later.

1. while in your docker command, and that you have logged into your docker registry (*docker login command), now run the push

docker push dbones/testnet

done. you can goto docker hub and see the image.

Step 4 - install and run.

ok there are a couple of ways, it depends on your setup, i would recondmend looking into a docker orchestrator such as Rancher, kubernetes etc.

A) using pure docker

if you want to run docker directly, no compose or orchestrator, that is not a problem, just follow these instructions.

1. on the linux server with docker installed call the following command.

docker run -p 8080:80 -d dbones/testnet

this exposes port 80 of the container on port 8080 on the host pc, to test this

• curl http://0.0.0.0:8080 and it would access your site
• docker ps would list all active containers on the server, our container should be listed.

B) using Rancher UI

this assumes we have the following setup:

• 2 servers with a label of server=application and
• 1 server with a label of server=proxy

in this setup we access the Nancy application through a load-balancer

1. create a stack called test
2. copy the following into the docker-compose.yaml and docker-compose-yaml boxes.

docker-compose.yaml

hello-world-lb:
  ports:
  - 80:80
  labels:
    io.rancher.scheduler.affinity:host_label: server=proxy
  tty: true
  image: rancher/load-balancer-service
  links:
  - hello-world:hello-world
  stdin_open: true
hello-world:
  labels:
    io.rancher.scheduler.affinity:container_ne: hello-world
    io.rancher.scheduler.affinity:host_label: server=application
  tty: true
  image: dbones/testnet
  stdin_open: true

rancher-compose.yaml

hello-world-lb:
  scale: 1
  health_check:
    port: 42
    interval: 2000
    unhealthy_threshold: 3
    healthy_threshold: 2
    response_timeout: 2000
hello-world:
  scale: 2
  health_check:
    port: 80
    interval: 2000
    unhealthy_threshold: 3
    request_line: GET / HTTP/1.0
    healthy_threshold: 2
    response_timeout: 2000

1. click on the play buttons.

you will now see that we have 3 containers deployed and running and that we can access the site through the proxy server.