CodeCamp cheatsheet

cheatsheet.md

Creating and Dockerizing an ASP.NET Core application

First of all, we need to add a reference to the Microsoft.AspNetCore.Server.Kestrel web server, version 1.1.0.

Then, we just create a very basic .NET Core application that creates a web host and runs it, with a very basic response to every request.

using System;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;

	public static void Main(string[] args)
        {
            var host = new WebHostBuilder()
                .UseKestrel()
                .Configure(app => app.Run(context => 
                {
                    return context.Response.WriteAsync($"Hello, Universe! It is {DateTime.Now}");
                }))
                .Build();

            host.Run();
        }

Now, if we run the application using dotnet restore and dotnet run and we go to http://localhost:5000, we can see the reply.

Now we want this application to run inside Docker, so we add a new Dockerfile. We can do this either with the help of VS Code, or we write the entire file ourselves. Either way, the file is pretty straightforward:

FROM microsoft/dotnet:1.1.0-sdk-projectjson

COPY . /app
WORKDIR /app

RUN ["dotnet", "restore"]
RUN ["dotnet", "build"]

EXPOSE 5000/tcp
ENV ASPNETCORE_URLS http://*:5000

ENTRYPOINT ["dotnet", "run"]

At this point, we have configured our application (that wasn't that hard), we have a definition file for Docker, our Dockerfile, but we haven't built an image or a container so far.

The end result is for us to start a container. Every container is built upon an image, that is composed of the application itself and of the dependencies.

To build the image, simply run the following command:

docker build -t awesome-live-demo .

• docker build - the command that builds the image
• -t awesome-live-demo - just the image tag, so you can find your image
• . - the dot specifies that the Dockerfile is present in the current directory of the command

Running this command will take every line from the Dockerfile.

At this point, we have a Docker image and we want to run a container based on that image:

docker run -d -p 8080:5000 -t awesome-live-demo

• -d - the container will run in detached mode
• -p 8080:5000 - will map the port 5000 from the container (that the app is running on) to port 8080 from the host.
• -t - specifies the tag of the image, so the new container is based on that image.

Now, if we go to http://localhost:8080 we can see the container running.

To create a new bash session on a running container: docker exec -i -t container_id bash

Moving to Docker Cloud

1. Create a Docker Hub image repository based on the GitHub repository we created

After configuring the repository, remember to set the build machine to be a node of yours, not a Docker machine

2. After that, simply update the repository to trigger a build

3. Next, we will create a service in Docker Cloud that will use (for now) the only image that we have, awesome-live-demo

4. Configure the desired ports on the host

To see information about a running container, simply run: docker-cloud container inspect container_id | grep port