Running and Exploring a Docker Linux Container

Sometimes the best way to troubleshoot and understand how a Docker Container works, is by exploring the Container. While I believe there are couple of ways to explore, one of the ways I really found useful is docker exec. Basically docker exec let’s you run commands inside a Container, and for a Linux Container we can use docker exec to bash in and run shell commands.

But to bash in of course, you need to have the Container in running state. Here in this post, I have explained how you can setup your own Container, specifically a Linux Container with ASP.NET Core MVC Application running inside.

So let’s proceed.

Currently I have no Containers running.

docker ps -a

And I have following set of Images.

docker images

Here the dockerwebapp is the Image that I am planning of creating and running a Container from. I can run the Container by issuing  docker run.

# Runs in the foreground
# Even if pressed Ctrl+C, Container is still running
PS C:\WINDOWS\system32> docker run dockerwebapp
 
# Runs in the background/detached
PS C:\WINDOWS\system32> docker run -d dockerwebapp
 
# Runs in the foreground
# If pressed Ctrl+C, Container will stop running
# Container will be displayed in docker ps -a
PS C:\WINDOWS\system32> docker run -it dockerwebapp
 
# Runs in the foreground
# If pressed Ctrl+C, Container will stop running and will get deleted
PS C:\WINDOWS\system32> docker run -it –-rm dockerwebapp

In this case, I am going to run docker run –d dockerwebapp as I want the Container to be running in the background, so for next docker commands, I don’t want to open up another PowerShell window.

docker run -d dockerwebapp

Now I can see that my container is running, it’s time to explore the image.

PS C:\WINDOWS\system32> docker exec -i -t blissful_roentgen /bin/bash
 
# -i -t can be use together like follows
PS C:\WINDOWS\system32> docker exec -it blissful_roentgen /bin/bash

docker exec

You can see that I am now in a Linux shell and I can use shell commands to explore the image. For instance to see the file system.

ls

Hope this helps.

Happy Coding.

Regards,
Jaliya

Running ASP.NET Core MVC Application inside a Docker Linux Container from Windows

I have been having some quality time with Docker recently and wanted to get an ASP.NET Core application running in a Docker Linux Container which will run inside my Windows machine. Was having some hard time getting it to work initially, but with some great help and guidance from a fellow MVP, Alex Thissen (@alexthissen), managed to get it up and running.

Here in this post, I assume you have some basic knowledge on Docker, Docker Images/Containers. And for some of the commands, I might not be explaining what each arguments of the command does, hoping you will do --help on those.

So let’s start.

So on my machine, I have Docker for Windows installed, and there under settings, I have my local C:\ drive shared with Containers.

Shared Drives

Now let’s create a folder (I am creating on my Desktop, make sure the drive you are creating the folder in, is shared like above) and I am naming it as a DockerWebApp.

Open up a PowerShell window and change the directory to DockerWebApp folder.

PS C:\Users\Jaliya\Desktop\DockerWebApp> dotnet new mvc
PS C:\Users\Jaliya\Desktop\DockerWebApp> dotnet restore
PS C:\Users\Jaliya\Desktop\DockerWebApp> code .

Now the project will get opened in Visual Studio Code. I have Docker extension for VS Code installed. If you haven’t installed, I suggest you do so, so we can create Docker related files pretty easily. So using the extension, I am creating a Dockerfile as follows.

Docker for VS Code - Adding Dockerfile

So my Dockerfile looks like this.

FROM microsoft/aspnetcore:1.0.1
LABEL Name=dockerwebapp Version=0.0.1
ARG source=.
WORKDIR /app
EXPOSE 30000
COPY $source .
ENTRYPOINT dotnet dockerwebapp.dll

For now, I am not going to do any changes here, but I am going to delete the other Docker files which got created inside the project which are docker-compose.debug.yml and docker-compose.yml to make things not confusing.

Now let’s publish our application.

PS C:\Users\Jaliya\Desktop\DockerWebApp> dotnet publish -c Release

And since I haven’t specify any specific output path, application will get published to bin\Release\netcoreapp1.1\publish folder.

Publish folder

Now let’s move to back to our Dockerfile and do following changes.

FROM microsoft/aspnetcore:1.0.1
LABEL Name=dockerwebapp Version=0.0.1
ARG source
WORKDIR /app
EXPOSE 30000
COPY ${source:-bin/Release/netcoreapp1.1/publish} .
ENTRYPOINT dotnet DockerWebApp.dll

Here first what I have done is, I don’t want to copy the whole project folder to my Image, I am just copying the publish folder. Then I have renamed the dll name in the ENTRYPOINT as in the file name in the publish folder (well I have spent quite sometime figuring out an issue because of this name mismatch).

Now let’s build the Docker Image, so I can create a Container out of it.

For that I am running the following command.

PS C:\Users\Jaliya\Desktop\DockerWebApp> docker build -t dockerwebapp .

I am seeing the following output.

docker build -t dockerwebapp .

All seem to be good, there is a warning at the end, we can basically ignore that for now for the sake of this demo. Now let’s run the following command to confirm whether our image is created.

PS C:\Users\Jaliya\Desktop\DockerWebApp> docker images

docker images

Yes, it is created, now let’s try to run it.

PS C:\Users\Jaliya\Desktop\DockerWebApp> docker run dockerwebapp

Now I am getting an error “The specified framework 'Microsoft.NETCore.App', version '1.1.2' was not found.”.

docker run dockerwebapp

Of course, I have been using an older aspnetcore image, I am changing the Dockerfile as follows.

FROM microsoft/aspnetcore:1.1.2
LABEL Name=dockerwebapp Version=0.0.1
ARG source
WORKDIR /app
EXPOSE 30000
COPY ${source:-bin/Release/netcoreapp1.1/publish} .
ENTRYPOINT dotnet DockerWebApp.dll

Here is the link where you can find the list ASP.NET Core Docker image information.

https://hub.docker.com/r/microsoft/aspnetcore/

Now let’s run a docker build again.

PS C:\Users\Jaliya\Desktop\DockerWebApp> docker build -t dockerwebapp .

docker build -t dockerwebapp .

Now let’s run the image again.

docker run dockerwebapp

Yes, it seem to be working. Let’s run the following command in a new PowerShell Window to see the status of all the running Containers.

PS C:\Users\Jaliya> docker ps

Here note that I am running the command from another directory. You can run docker ps from sitting inside any directory.

docker ps -a

Now from let’s try to access to site http://localhost:30000 from a browser.

Site can't be reached

That’s because I haven’t mapped Container ports and host machines ports. I can easily to fix it by running docker run specifying port mappings.

PS C:\Users\Jaliya\Desktop\DockerWebApp> docker run -p 30000:80 dockerwebapp

docker run -p 30000:80 dockerwebapp

And now if I check for running Containers, I can see the ports are mapped.

docker ps

Now let’s browse to http://localhost:30000 back again. And this time, it works!

Site is running

In this post, I have used following commands in the background.

# List running containers
docker ps
 
# List all containers
docker ps -a
 
# List all images
docker images
 
# Stop given container
docker stop {container_name}

# Stop all containers
docker stop $(docker ps -aq)
 
# Delete given container
docker rm {container_name}
 
# Delete given image
docker rmi {image_id}
 
# Delete all containers
docker rm $(docker ps -a -q)
 
# Delete all images
docker rmi $(docker images -q)

# Remove all stopped containers
docker container prune

# Remove all images which are not used by existing containers
docker image prune -a

# Remove all unused containers, networks, images (both dangling and unreferenced), and optionally, volumes.
docker system prune

Hope you find this post helpful.

Again huge thanks goes out to Alex Thissen (@alexthissen) for all his help.

More reads,
Running and Exploring a Docker Linux Container

Happy Coding.

Regards,
Jaliya

Visual C# Technical Guru - April 2017

Another month as a judge in Microsoft TechNet Guru Awards under Visual C# category. The TechNet Guru Awards celebrate the technical articles on Microsoft TechNet.

Post in WikiNinjas Official Blog,
https://blogs.technet.microsoft.com/wikininjas/2017/05/16/april-2017-technet-guru-winners/

Visual C# Technical Guru - April 2017

Happy Coding.

Regards,
Jaliya

Windows Subsystem for Linux

With Windows 10 Creators Update one of the features that got released publicly is Windows Subsystem for Linux (WSL). But it was available for Windows 10 Insiders for almost like a year now and was initially announced at Build 2016. WSL basically let’s you run Linux on Windows. If you are thinking about a VM, No, it’s not a Virtual Machine.

Configuring WSL on Windows shouldn’t take more than 10 minutes, by following these steps you can configure WSL pretty easily. Once you have configured WSL, you should be able use Bash on Ubuntu, just by opening up the Command Prompt/PowerShell and running bash command.

WSL

Or you can Search for Bash in Windows, and there should be a desktop app named Bash on Ubuntu on Windows.

Bash On Ubuntu On Windows

Currently under WSL only Ubuntu is supported, may be in the future Microsoft might support different flavors of Linux.

On WSL, one of the things that fascinates me more is the File System that is already mounted for you.

File System

And through the bash I can just run mkdir and the folder will be appearing inside Windows Explorer the same time.

And most importantly I can run .NET Core Apps on WSL. I have installed .NET Core on my WSL, (again it’s pretty easy, just follow the relevant steps described here) and created an ASP.NET Core HelloWorld application.

.NET Core on WSL

And I can just browse the site from a Web Browser in my Windows OS. Isn’t that just great?

Happy Coding.

Regards,
Jaliya