Migrate custom software to Azure App Service using a custom container

Azure App Service provides pre-defined application stacks on Windows like ASP.NET or Node.js, running on IIS. The preconfigured Windows environment locks down the operating system from administrative access, software installations, changes to the global assembly cache, and so on (see Operating system functionality on Azure App Service). However, using a custom Windows container in App Service (Preview) lets you make OS changes that your app needs, so it's easy to migrate on-premises app that requires 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.

Shows the web app running in a Windows container.

Prerequisites

To complete this tutorial:

Set up the app locally

Download the sample

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

The sample project contains a simple ASP.NET application that uses a custom font that is installed into the Windows font library. It's not necessary to install fonts, but it's an example of an app that is 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/CustomFontSample.sln file in Visual Studio.

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

Screenshot showing the app displayed in the default browser.

Because it 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.

Screenshot of the Solution Explorer window showing the CustomFontSample project, Add, and Container Orchestrator Support menu items selected.

Select Docker Compose > OK.

Your project is now set up 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 Script Center.

Note

To test the Windows container locally, make sure that Docker is started on your local machine.

Publish to Azure Container Registry

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

Open publish wizard

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

Screenshot of Solution Explorer showing the CustomFontSample project and Publish selected.

Create registry and publish

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

Screenshot of the publish wizard showing Container Registry, Create New Azure Container Registry, and the Publish button selected.

Sign in with Azure account

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

Sign in to Azure

Configure the registry

Configure the new container registry based on the suggested values in the following table. When finished, click Create.

Setting Suggested value For more information
DNS Prefix Keep the generated registry name, or change it to another unique name.
Resource Group Click New, type myResourceGroup, and click OK.
SKU Basic Pricing tiers
Registry Location West Europe

Configure Azure container registry

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

Sign in to Azure

Sign in to the Azure portal at https://portal.azure.com.

Create a web app

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

Configure app basics

In the Basics tab, configure the settings according to the following table, then click Next: Docker.

Setting Suggested value For more information
Subscription Make sure the correct subscription is selected.
Resource Group Select Create new, type myResourceGroup, and click OK.
Name Type a unique name. The URL of the web app is http://<app-name>.azurewebsites.net, where <app-name> is your app name.
Publish Docker container
Operating System Windows
Region West Europe
Windows Plan Select Create new, type myAppServicePlan, and click OK.

Your Basics tab should look like this:

Shows the Basics tab used to configure the web app.

Configure Windows container

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

Setting Suggested value
Image Source Azure Container Register
Registry Select the registry you created earlier.
Image customfontsample
Tag latest

Complete app creation

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

Browse to the web app

When the Azure operation is complete, a notification box is displayed.

Shows that the Azure operation is complete.

  1. Click Go to resource.

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

A new browser page is opened to the following page:

Shows the new browser page for the web app.

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

Shows the homepage with the font you configured.

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

See container start-up logs

It may take some time for the Windows container to load. To see the progress, navigate to the following URL by replacing <app-name> with the name of your app.

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

The streamed logs looks 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 --linux'. If those images don't satisfy your needs, you can build and deploy a custom image.

In this tutorial, you learn how to:

  • Build a custom image if no built-in image satisfies your needs
  • Push the custom image to a private container registry on Azure
  • Run the custom image in App Service
  • Configure environment variables
  • Update and redeploy the image
  • Access diagnostic logs
  • Connect to the container using SSH

Completing this tutorial incurs a small charge in your Azure account for the container registry and can incur additional costs for hosting the container for longer than a month.

Set up your initial environment

  • Have an Azure account with an active subscription. Create an account for free.
  • Install Docker, which you use to build Docker images. Installing Docker may require a computer restart.
  • Use Azure Cloud Shell using the bash environment.

    Embed launch

  • If you prefer, install the Azure CLI to run CLI reference commands.

    • If you're using a local install, sign in with Azure CLI by using the az login command. To finish the authentication process, follow the steps displayed in your terminal. See Sign in with Azure CLI for additional sign-in options.
    • When you're prompted, install Azure CLI extensions on first use. For more information about extensions, see Use extensions with Azure CLI.
    • Run az version to find the version and dependent libraries that are installed. To upgrade to the latest version, run az upgrade.
  • This tutorial requires version 2.0.80 or later of the Azure CLI. If using Azure Cloud Shell, the latest version is already installed.

After installing Docker or running Azure Cloud Shell, open a terminal window and verify that 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

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

Then go into that 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, select Clone, and then select Download ZIP.

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

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

(Optional) Examine the Docker file

The file in the sample named Dockerfile that 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 create an SSH server for secure 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

Note

Docker Hub has quotas on the number of anonymous pulls per IP and the number of authenticated pulls per free user (see Data transfer). If you notice your pulls from Docker Hub are being limited, try docker login if you're not already logged in.

  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 -p 8000:8000 appsvc-tutorial-custom-image
    

    This docker run command specifies the port with the -p argument followed by the name of the image.

    Tip

    If you are 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 CR-LF 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 the web app and container are functioning correctly.

    Test web app locally

Create a resource group

In this section and those that follow, you provision resources in Azure to which you push the image and then deploy a container to Azure App Service. You start by creating a resource group in which to collect all these resources.

Run the az group create command to create a resource group:

az group create --name AppSvc-DockerTutorial-rg --location westus2

You can change the --location value to specify a region near you.

Push the image to Azure Container Registry

In this section, you push the image to Azure Container Registry from which App Service can deploy it.

  1. Run the az acr create command to create an Azure Container Registry:

    az acr create --name <registry-name> --resource-group AppSvc-DockerTutorial-rg --sku Basic --admin-enabled true
    

    Replace <registry-name> with a suitable name for your registry. The name must contain only letters and numbers and must be unique across all of Azure.

  2. Run the az acr show command to retrieve credentials for the registry:

    az acr credential show --resource-group AppSvc-DockerTutorial-rg --name <registry-name>
    

    The JSON output of this command provides two passwords along with the registry's user name.

  3. 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 step.

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

  4. Once the login succeeds, tag your local Docker image for the registry:

    docker tag appsvc-tutorial-custom-image <registry-name>.azurecr.io/appsvc-tutorial-custom-image:latest
    
  5. 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.

  6. Use the az acr repository list command to verify that the push was successful:

    az acr repository list -n <registry-name>
    

    The output should show the name of your image.

Configure App Service to deploy the image from the registry

To deploy a container to Azure App Service, you first create a web app on App Service, then connect the web app to the container registry. When the web app starts, App Service automatically pulls the image from the registry.

  1. Create an App Service plan using the az appservice plan create command:

    az appservice plan create --name AppSvc-DockerTutorial-plan --resource-group AppSvc-DockerTutorial-rg --is-linux
    

    An App Service plan corresponds to the virtual machine that hosts the web app. By default, the previous command uses an inexpensive B1 pricing tier that is free for the first month. You can control the tier with the --sku parameter.

  2. Create the web app with the az webpp create command:

    az webapp create --resource-group AppSvc-DockerTutorial-rg --plan AppSvc-DockerTutorial-plan --name <app-name> --deployment-container-image-name <registry-name>.azurecr.io/appsvc-tutorial-custom-image:latest
    

    Replace <app-name> with a name for the web app, which must be unique across all of Azure. Also replace <registry-name> with the name of your registry from the previous section.

  3. Use az webapp config appsettings set to set the WEBSITES_PORT environment variable as expected by the app code:

    az webapp config appsettings set --resource-group AppSvc-DockerTutorial-rg --name <app-name> --settings WEBSITES_PORT=8000
    

    Replace <app-name> with the name you used in the previous step.

    For more information on this environment variable, see the readme in the sample's GitHub repository.

  4. Enable managed identity for the web app by using the az webapp identity assign command:

    az webapp identity assign --resource-group AppSvc-DockerTutorial-rg --name <app-name> --query principalId --output tsv
    

    Replace <app-name> with the name you used in the previous step. The output of the command (filtered by the --query and --output arguments) is the service principal of the assigned identity, which you use shortly.

    Managed identity allows you to grant permissions to the web app to access other Azure resources without needing any specific credentials.

  5. Retrieve your subscription ID with the az account show command, which you need in the next step:

    az account show --query id --output tsv
    
  6. Grant the web app permission to access the container registry:

    az role assignment create --assignee <principal-id> --scope /subscriptions/<subscription-id>/resourceGroups/AppSvc-DockerTutorial-rg/providers/Microsoft.ContainerRegistry/registries/<registry-name> --role "AcrPull"
    

    Replace the following values:

    • <principal-id> with the service principal ID from the az webapp identity assign command
    • <registry-name> with the name of your container registry
    • <subscription-id> with the subscription ID retrieved from the az account show command

For more information about these permissions, see What is Azure role-based access control and

Deploy the image and test the app

You can complete these steps once the image is pushed to the container registry and the App Service is fully provisioned.

  1. Use the az webapp config container set command to specify the container registry and the image to deploy for the web app:

    az webapp config container set --name <app-name> --resource-group AppSvc-DockerTutorial-rg --docker-custom-image-name <registry-name>.azurecr.io/appsvc-tutorial-custom-image:latest --docker-registry-server-url https://<registry-name>.azurecr.io
    

    Replace <app_name> with the name of your web app and replace <registry-name> in two places with the name of your registry.

    • When using a registry other than Docker Hub (as this example shows), --docker-registry-server-url must be formatted as https:// followed by the fully qualified domain name of the registry.
    • The message, "No credential was provided to access Azure Container Registry. Trying to look up..." tells you that Azure is using the app's managed identity to authenticate with the container registry rather than asking for a username and password.
    • If you encounter the error, "AttributeError: 'NoneType' object has no attribute 'reserved'", make sure your <app-name> is correct.

    Tip

    You can retrieve the web app's container settings at any time with the command az webapp config container show --name <app-name> --resource-group AppSvc-DockerTutorial-rg. The image is specified in the property DOCKER_CUSTOM_IMAGE_NAME. When the web app is deployed through Azure DevOps or Azure Resource Manager templates, the image can also appear in a property named LinuxFxVersion. Both properties serve the same purpose. If both are present in the web app's configuration, LinuxFxVersion takes precedence.

  2. Once the az webapp config container set command completes, the web app should be running in the container on App Service.

    To test the app, browse to http://<app-name>.azurewebsites.net, replacing <app-name> with the name of your web app. On first access, it may 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.

    Successful test of the web app on Azure

Modify the app code and redeploy

In this section, you make a change to the web app code, rebuild the container, and then push the container to the 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 version number in the image's tag to v1.0.1:

    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. Restart the web app:

    az webapp restart --name <app_name> --resource-group AppSvc-DockerTutorial-rg
    

    Replace <app_name> with the name of your web app. Upon restart, App Service pulls the updated image from the container registry.

  8. Verify that the update has been deployed by browsing to http://<app-name>.azurewebsites.net.

Access diagnostic logs

  1. Turn on container logging:

    az webapp log config --name <app-name> --resource-group AppSvc-DockerTutorial-rg --docker-container-logging filesystem
    
  2. Enable the log stream:

    az webapp log tail --name <app-name> --resource-group AppSvc-DockerTutorial-rg
    

    If you don't see console logs immediately, check again in 30 seconds.

    You can also inspect the log files from the browser at https://<app-name>.scm.azurewebsites.net/api/logs/docker.

  3. To stop log streaming at any time, type Ctrl+C.

Connect to the container using SSH

SSH enables secure communication between a container and a client. To enable SSH connection to your container, your custom image must be configured for it. Once 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 login 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 

Note

This configuration doesn't allow external connections to the container. SSH is available only through the Kudu/SCM Site. The Kudu/SCM site is authenticated with your Azure account.

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 SSH connection to container

  1. Browse to https://<app-name>.scm.azurewebsites.net/webssh/host and sign in with your Azure account. Replace <app-name> with the name of your web app.

  2. Once signed in, you're redirected to an informational page for the web app. Select SSH at the top of the page to open the shell and use commands.

    For example, you can examine the processes running within it using the top command.

Clean up resources

The resources you created in this article may incur ongoing costs. to clean up the resources, you need only delete the resource group that contains them:

az group delete --name AppSvc-DockerTutorial-rg

Next steps

What you learned:

  • Deploy a custom image to a private container registry
  • Deploy and the custom image in App Service
  • Update and redeploy the image
  • Access diagnostic logs
  • Connect to the container using SSH

In the next tutorial, you learn how to map a custom DNS name to your app.

Or, check out other resources: