Migrate custom software to Azure App Service using a custom container

Azure App Service provides pre-defined application stacks, like ASP.NET or Node.js, on Windows. These application stacks run on IIS. The preconfigured Windows environment locks down the operating system from:

• Administrative access.
• Software installations.
• Changes to the global assembly cache.

For more information, see Operating system functionality on Azure App Service.

You can deploy a custom-configured Windows image from Visual Studio to make OS changes that your app needs. This makes it easy to migrate an on-premises app that requires a custom OS and software configuration. This tutorial demonstrates how to migrate to App Service an ASP.NET app that uses custom fonts installed in the Windows font library. You deploy a custom-configured Windows image from Visual Studio to Azure Container Registry and then run it in App Service.

Prerequisites

To complete this tutorial:

• Sign up for a Docker Hub account.
• Install Docker for Windows.
• Configure Docker to run Windows containers.
• Install Visual Studio 2022 with the ASP.NET and web development and Azure development workloads. If you've installed Visual Studio 2022 already:
  • Install the latest updates in Visual Studio by selecting Help > Check for Updates.
  • Add the workloads in Visual Studio by selecting Tools > Get Tools and Features.

Set up the app locally

Download the sample

In this step, you set up the local .NET project.

• Download the sample project.
• Extract (unzip) the custom-font-win-container-master.zip file.

The sample project contains a simple ASP.NET application that uses a custom font that's installed into the Windows font library. It's not necessary to install fonts. However, the sample is an example of an app that's integrated with the underlying OS. To migrate such an app to App Service, you either rearchitect your code to remove the integration, or migrate it as-is in a custom Windows container.

Install the font

In Windows Explorer, navigate to custom-font-win-container-master/CustomFontSample, right-click FrederickatheGreat-Regular.ttf, and select Install.

This font is publicly available from Google Fonts.

Run the app

Open the custom-font-win-container-master/CustomFontSample.sln file in Visual Studio.

Select Ctrl+F5 to run the app without debugging. The app is displayed in your default browser.

As the app uses an installed font, the app can't run in the App Service sandbox. However, you can deploy it using a Windows container instead, because you can install the font in the Windows container.

Configure Windows container

In Solution Explorer, right-click the CustomFontSample project and select Add > Container Orchestration Support.

Select Docker Compose > OK.

Your project is now set to run in a Windows container. A Dockerfile is added to the CustomFontSample project, and a docker-compose project is added to the solution.

From the Solution Explorer, open Dockerfile.

You need to use a supported parent image. Change the parent image by replacing the FROM line with the following code:

FROM mcr.microsoft.com/dotnet/framework/aspnet:4.7.2-windowsservercore-ltsc2019

At the end of the file, add the following line and save the file:

RUN ${source:-obj/Docker/publish/InstallFont.ps1}

You can find InstallFont.ps1 in the CustomFontSample project. It's a simple script that installs the font. You can find a more complex version of the script in the PowerShell Gallery.

Publish to Azure Container Registry

Azure Container Registry can store your images for container deployments. You can configure App Service to use images that are hosted in Azure Container Registry.

Open the publish wizard

In the Solution Explorer, right-click the CustomFontSample project and select Publish.

Create and publish the registry

In the publish wizard, select Container Registry > Create New Azure Container Registry > Publish.

Sign in with an Azure account

In the Create a new Azure Container Registry dialog, select Add an account, and then sign in to your Azure subscription. If you're already signed in, select the account containing the desired subscription from the dropdown.

Configure the registry

Configure the new container registry by using the suggested values in the following table as a guide. When finished, select Create.

A terminal window opens and displays the image deployment progress. Wait for the deployment to complete.

Sign in to Azure

Sign in to the Azure portal.

Create a web app

From the left menu, select Create a resource > Web > Web App for Containers.

Configure app basics

On the Basics tab, configure the settings according to the following table. Then select Next: Docker.

Your Basics tab should look like this:

Configure the Windows container

On the Docker tab, configure your custom Windows container as shown in the following table, and then select Review + create.

Complete app creation

Select Create and wait for Azure to create the required resources.

Browse to the web app

When the deployment is complete, a notification box is displayed.

1. Select Go to resource.

2. In the app page, select the link under URL.

A new browser page is opened to the following page:

Wait a few minutes and try again, until you get the homepage with the font you expect:

Congratulations! You've migrated an ASP.NET application to Azure App Service in a Windows container.

View the container start-up logs

It might take some time for the Windows container to load. To see the progress, go to the following URL. (Replace <app-name> with the name of your app.)

https://<app-name>.scm.azurewebsites.net/api/logstream

The streamed logs look like this:

14/09/2018 23:16:19.889 INFO - Site: fonts-win-container - Creating container for image: customfontsample20180914115836.azurecr.io/customfontsample:latest.
14/09/2018 23:16:19.928 INFO - Site: fonts-win-container - Create container for image: customfontsample20180914115836.azurecr.io/customfontsample:latest succeeded. Container Id 329ecfedbe370f1d99857da7352a7633366b878607994ff1334461e44e6f5418
14/09/2018 23:17:23.405 INFO - Site: fonts-win-container - Start container succeeded. Container: 329ecfedbe370f1d99857da7352a7633366b878607994ff1334461e44e6f5418
14/09/2018 23:17:28.637 INFO - Site: fonts-win-container - Container ready
14/09/2018 23:17:28.637 INFO - Site: fonts-win-container - Configuring container
14/09/2018 23:18:03.823 INFO - Site: fonts-win-container - Container ready
14/09/2018 23:18:03.823 INFO - Site: fonts-win-container - Container start-up and configuration completed successfully

Azure App Service uses the Docker container technology to host both built-in images and custom images. To see a list of built-in images, run the Azure CLI command, 'az webapp list-runtimes --os linux'. If those images don't satisfy your needs, you can build and deploy a custom image.

In this tutorial, you learn how to:

Completing this tutorial incurs a small charge in your Azure account for the container registry and can incur more costs if you host the container for longer than a month.

Set up your initial environment

This tutorial requires version 2.0.80 or later of the Azure CLI. If you're using Azure Cloud Shell, the latest version is already installed.

• Have an Azure account with an active subscription. Create an account for free.

• Use the Bash environment in Azure Cloud Shell. For more information, see Quickstart for Bash in Azure Cloud Shell.

  

• If you prefer to run CLI reference commands locally, install the Azure CLI. If you're running on Windows or macOS, consider running Azure CLI in a Docker container. For more information, see How to run the Azure CLI in a Docker container.

  • If you're using a local installation, sign in to the Azure CLI by using the az login command. To finish the authentication process, follow the steps displayed in your terminal. For other sign-in options, see Sign in with the Azure CLI.

  • When you're prompted, install the Azure CLI extension on first use. For more information about extensions, see Use extensions with the Azure CLI.

  • Run az version to find the version and dependent libraries that are installed. To upgrade to the latest version, run az upgrade.

• Install Docker, which you use to build Docker images. Installing Docker might require a computer restart.

After installing Docker, open a terminal window and verify that the docker is installed:

docker --version

Clone or download the sample app

You can obtain the sample for this tutorial via git clone or download.

Clone with Git

Clone the sample repository:

git clone https://github.com/Azure-Samples/docker-django-webapp-linux.git --config core.autocrlf=input

Ensure that you include the --config core.autocrlf=input argument to guarantee proper line endings in files that are used inside the Linux container.

Then navigate to the folder:

cd docker-django-webapp-linux

Download from GitHub

Instead of using git clone, you can visit https://github.com/Azure-Samples/docker-django-webapp-linux and select Code > Local > Download ZIP.

Unpack the ZIP file into a folder named docker-django-webapp-linux.

Then open a terminal window in the docker-django-webapp-linux folder.

(Optional) Examine the Docker file

This is the file in the sample that's named Dockerfile. It describes the Docker image and contains configuration instructions.

FROM tiangolo/uwsgi-nginx-flask:python3.6

RUN mkdir /code
WORKDIR /code
ADD requirements.txt /code/
RUN pip install -r requirements.txt --no-cache-dir
ADD . /code/

# ssh
ENV SSH_PASSWD "root:Docker!"
RUN apt-get update \
        && apt-get install -y --no-install-recommends dialog \
        && apt-get update \
 && apt-get install -y --no-install-recommends openssh-server \
 && echo "$SSH_PASSWD" | chpasswd 

COPY sshd_config /etc/ssh/
COPY init.sh /usr/local/bin/

RUN chmod u+x /usr/local/bin/init.sh
EXPOSE 8000 2222

#CMD ["python", "/code/manage.py", "runserver", "0.0.0.0:8000"]
ENTRYPOINT ["init.sh"]

• The first group of commands installs the app's requirements in the environment.
• The second group of commands creates an SSH server to provide improved-security communication between the container and the host.
• The last line, ENTRYPOINT ["init.sh"], invokes init.sh to start the SSH service and Python server.

Build and test the image locally

1. Run the following command to build the image:

   docker build --tag appsvc-tutorial-custom-image .
   

2. Test that the build works by running the Docker container locally:

   docker run -it -p 8000:8000 appsvc-tutorial-custom-image
   

   This docker run command specifies the port with the -p argument and includes the name of the image. -it lets you stop it with Ctrl+C.

   Tip

   If you're running on Windows and see the error standard_init_linux.go:211: exec user process caused "no such file or directory", the init.sh file contains CRLF line endings instead of the expected LF endings. This error happens if you used Git to clone the sample repository but omitted the --config core.autocrlf=input parameter. In this case, clone the repository again with the --config argument. You might also see the error if you edited init.sh and saved it with CRLF endings. In this case, save the file again with LF endings only.

3. Browse to http://localhost:8000 to verify that the web app and container are functioning correctly.

   

I. Create a user-assigned managed identity

App Service can use either a default managed identity or a user-assigned managed identity to authenticate with a container registry. In this tutorial, you'll use a user-assigned managed identity.

II. Create a container registry

III. Push the sample image to Azure Container Registry

In this section, you push the image to Azure Container Registry, which will be used by App Service later.

1. From the local terminal where you built the sample image, use the docker login command to sign in to the container registry:

   docker login <registry-name>.azurecr.io --username <registry-username>
   

   Replace <registry-name> and <registry-username> with values from the previous steps. When prompted, type in one of the passwords from the previous section.

   You use the same registry name in all the remaining steps of this section.

2. When the sign-in is successful, tag your local Docker image to the registry:

   docker tag appsvc-tutorial-custom-image <registry-name>.azurecr.io/appsvc-tutorial-custom-image:latest
   

3. Use the docker push command to push the image to the registry:

   docker push <registry-name>.azurecr.io/appsvc-tutorial-custom-image:latest
   

   Uploading the image the first time might take a few minutes because it includes the base image. Subsequent uploads are typically faster.

   While you're waiting, you can complete the steps in the next section to configure App Service to deploy from the registry.

IV. Authorize the managed identity for your registry

The managed identity you created doesn't have authorization to pull from the container registry yet. In this step, you enable the authorization.

V. Create the web app

VI. Configure the web app

In this step, you configure the web app as follows:

• Configure the app to send requests to port 8000. The sample container is listening on port 8000 for web requests.
• Tell your app to use the managed identity to pull images from your container registry.
• Configure continuous deployment from the container registry (every image push to the registry will trigger your app to pull the new image). This part isn't needed for your web app to pull from your container registry, but it can let your web app know when a new image is pushed to the registry. Without it, you must manually trigger an image pull by restarting the web app.

VII. Browse to the web app

The first time you attempt to access the app, it might take some time for the app to respond because App Service must pull the entire image from the registry. If the browser times out, just refresh the page. Once the initial image is pulled, subsequent tests will run much faster.

VIII. Access diagnostic logs

IX. Modify the app code and redeploy

In this section, you make a change to the web app code, rebuild the image, and then push it to your container registry. App Service then automatically pulls the updated image from the registry to update the running web app.

1. In your local docker-django-webapp-linux folder, open the file app/templates/app/index.html.

2. Change the first HTML element to match the following code.

   <nav class="navbar navbar-inverse navbar-fixed-top">
     <div class="container">
       <div class="navbar-header">
         <a class="navbar-brand" href="#">Azure App Service - Updated Here!</a>
       </div>
     </div>
   </nav>
   

3. Save your changes.

4. Change to the docker-django-webapp-linux folder and rebuild the image:

   docker build --tag appsvc-tutorial-custom-image .
   

5. Update the image's tag to latest:

   docker tag appsvc-tutorial-custom-image <registry-name>.azurecr.io/appsvc-tutorial-custom-image:latest
   

   Replace <registry-name> with the name of your registry.

6. Push the image to the registry:

   docker push <registry-name>.azurecr.io/appsvc-tutorial-custom-image:latest
   

7. When the image push is complete, the webhook notifies App Service about the push, and App Service tries to pull in the updated image. Wait a few minutes, and then verify that the update has been deployed by browsing to https://<app-name>.azurewebsites.net.

X. Connect to the container using SSH

SSH enables improved-security communication between a container and a client. To enable an SSH connection to your container, you must configure your custom image for it. When the container is running, you can open an SSH connection.

Configure the container for SSH

The sample app used in this tutorial already has the necessary configuration in the Dockerfile, which installs the SSH server and also sets the sign-in credentials. This section is informational only. To connect to the container, skip to the next section.

ENV SSH_PASSWD "root:Docker!"
RUN apt-get update \
        && apt-get install -y --no-install-recommends dialog \
        && apt-get update \
  && apt-get install -y --no-install-recommends openssh-server \
  && echo "$SSH_PASSWD" | chpasswd 

The Dockerfile also copies the sshd_config file to the /etc/ssh/ folder and exposes port 2222 on the container:

COPY sshd_config /etc/ssh/

# ...

EXPOSE 8000 2222

Port 2222 is an internal port accessible only by containers within the bridge network of a private virtual network.

Finally, the entry script, init.sh, starts the SSH server.

#!/bin/bash
service ssh start

Open the SSH connection to the container

XI. Clean up resources

az group delete --name msdocs-custom-container-tutorial