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.

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. 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. However, the sample is 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-master/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.

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.

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 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, ensure 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, select Create.

Setting Suggested value For more information
DNS Prefix Keep the generated registry name, or change it to another unique name.
Resource Group Select New, type myResourceGroup, and select 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.

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 select Next: Docker.

Setting Suggested value For more information
Subscription Make sure the correct subscription is selected.
Resource Group Select Create new, type myResourceGroup, and select OK.
Name Type a unique name. The URL of the web app is https://<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 select 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

Select 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. Select Go to resource.

  2. In the app page, select 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 might take some time for the Windows container to load. To see the progress, go 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 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:

  • Push a custom Docker image to Azure Container Registry
  • Deploy the custom image to App Service
  • Configure environment variables
  • Pull image into App Service using a managed identity
  • Access diagnostic logs
  • Enable CI/CD from Azure Container Registry to App Service
  • Connect to the container using SSH

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

  • 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, 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 thedocker-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 -it -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. -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 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.

I. Create a user-assigned managed identity

App Service can either use 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.

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

    az group create --name msdocs-custom-container-tutorial --location westeurope
    

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

  2. Create a managed identity in the resource group.

    az identity create --name myID --resource-group msdocs-custom-container-tutorial
    

II. Create a container registry

  1. Create a container registry with the az acr create command and replace <registry-name> with a unique name for your registry. The name must contain only letters and numbers, and must be unique across all of Azure.

    az acr create --name <registry-name> --resource-group msdocs-custom-container-tutorial --sku Basic --admin-enabled true
    

    The --admin-enabled parameter lets you push images to the registry using a set of administrative credentials.

  2. Retrieve the administrative credentials by running the az acr show command:

    az acr credential show --resource-group msdocs-custom-container-tutorial --name <registry-name>
    

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

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 step.

    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.

  1. Retrieve the principal ID for the managed identity:

    principalId=$(az identity show --resource-group msdocs-custom-container-tutorial --name myID --query principalId --output tsv)
    
  2. Retrieve the resource ID for the container registry:

    registryId=$(az acr show --resource-group msdocs-custom-container-tutorial --name <registry-name> --query id --output tsv)
    
  3. Grant the managed identity permission to access the container registry:

    az role assignment create --assignee $principalId --scope $registryId --role "AcrPull"
    

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

V. Create the web app

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

    az appservice plan create --name myAppServicePlan --resource-group msdocs-custom-container-tutorial --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 webapp create command:

    az webapp create --resource-group msdocs-custom-container-tutorial --plan myAppServicePlan --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.

    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 msdocs-custom-container-tutorial. 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.

VI. Configure the web app

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

  • The sample container is listening on port 8000 for web requests, and you configure the app to send requests to port 8000.
  • Tell your app to use the managed identity to pull images from your container registry.
  • Configure continuous deployment from the container registry (or, 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.
  1. 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 msdocs-custom-container-tutorial --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.

  2. Enable the user-assigned managed identity in the web app with the az webapp identity assign command:

    id=$(az identity show --resource-group msdocs-custom-container-tutorial --name myID --query id --output tsv)
    az webapp identity assign --resource-group msdocs-custom-container-tutorial --name <app-name> --identities $id
    

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

  3. Configure your app to pull from Azure Container Registry by using managed identities.

    appConfig=$(az webapp config show --resource-group msdocs-custom-container-tutorial --name <app-name> --query id --output tsv)
    az resource update --ids $appConfig --set properties.acrUseManagedIdentityCreds=True
    

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

  4. Set the client ID your web app uses to pull from Azure Container Registry. This step isn't needed if you use the system-assigned managed identity.

    clientId=$(az identity show --resource-group msdocs-custom-container-tutorial --name myID --query clientId --output tsv)
    az resource update --ids $appConfig --set properties.AcrUserManagedIdentityID=$clientId
    
  5. Enable CI/CD in App Service.

    cicdUrl=$(az webapp deployment container config --enable-cd true --name <app-name> --resource-group msdocs-custom-container-tutorial --query CI_CD_URL --output tsv)
    

    CI_CD_URL is a URL that App Service generates for you. Your registry should use this URL to notify App Service that an image push occurred. It doesn't actually create the webhook for you.

  6. Create a webhook in your container registry using the CI_CD_URL you got from the last step.

    az acr webhook create --name appserviceCD --registry <registry-name> --uri $cicdUrl --actions push --scope appsvc-tutorial-custom-image:latest
    
  7. To test if your webhook is configured properly, ping the webhook, and see if you get a 200 OK response.

    eventId=$(az acr webhook ping --name appserviceCD --registry <registry-name> --query id --output tsv)
    az acr webhook list-events --name appserviceCD --registry <registry-name> --query "[?id=='$eventId'].eventResponseMessage"
    

    Tip

    To see all information about all webhook events, remove the --query parameter.

    If you're streaming the container log, you should see the message after the webhook ping: Starting container for site, because the webhook triggers the app to restart.

VII. Browse to the web app

To test the app, browse to https://<app-name>.azurewebsites.net, replacing <app-name> with the name of your web app.

On first access, 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.

A screenshot of the browser showing web app running successfully in Azure.

VIII. Access diagnostic logs

While you're waiting for the App Service to pull in the image, it's helpful to see exactly what App Service is doing by streaming the container logs to your terminal.

  1. Turn on container logging:

    az webapp log config --name <app-name> --resource-group msdocs-custom-container-tutorial --docker-container-logging filesystem
    
  2. Enable the log stream:

    az webapp log tail --name <app-name> --resource-group msdocs-custom-container-tutorial
    

    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.

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 the 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 secure communication between a container and a client. To enable SSH connection to your container, your custom image must be configured 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 

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. root:Docker! should not be altered SSH. SCM/KUDU will use your Azure Portal credentials. Changing this value will result in an error when using SSH.

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. When you sign 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.

XI. Clean up resources

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

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

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
  • Push a custom Docker image to Azure Container Registry
  • Deploy the custom image to App Service
  • Configure environment variables
  • Pull image into App Service using a managed identity
  • Access diagnostic logs
  • Enable CI/CD from Azure Container Registry to App Service
  • 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: