How to build a scalable C# web application in DockerFile for Container App in Azure Function?

Eric Wei
4 Min To Read
27 Oct, 2024
- Azure

Azure Function is a serverless and managed service. Now Azure also has released Container App plan which can allow you to easily build and deploy a custom doecker in web application to Azure Container App in Azunre Function.

You can enjoy building a high performance and scalable web application without worrying about how to manage and maintain Kubernete platform with Azure Container App.

How to get started?

I haved tried to ask ChatGPT to provide an example for Docker File.

However, it always provides a wrong example and its solution usually does not work out.

Because I think ChatGTP might not have correct and the latest training data for Azure Function’s Container App at this moment.

In this post, we will provide a Docker File in C# for you to build a high performance and scalable web appliction in Azure Function with Container App.

Create Azure Container Registry

In this tutorial, we create api_server_image as an example.

Next, we start to build your web aplication in Docker File.

Build DockerFile

You can log in to Azure

az login

STEP2: Build Web Application in C#

This following shows how to build C# web application.

Use a light weight linux image apline-linux: sdk:8.0.401-alpine3.20 to build C# web appliction This is usefull for building micro-service requiring fast startup time and efficency
The outputted x.dll files will save in /home/site/wwwroot
Then copy /home/site/wwwroot to runtime image at /dotnet-isolated:4-dotnet-isolated8.0
This runtime image: /dotnet-isolated:4-dotnet-isolated8.0 is built for isoloated mode of Azure Function in .NET v8

# Use a light weight linux to build C# web appliction
FROM mcr.microsoft.com/dotnet/sdk:8.0.401-alpine3.20 AS installer-env

RUN mkdir /app
WORKDIR /app

COPY . .

# Restore the dependencies (NuGet packages)
RUN dotnet restore "./<Your VS Project>.csproj"

# Build and publish the application to the /app directory
RUN dotnet publish "./<Your VS Project>.csproj" -c Debug -r $BUILD_RUN_TIME -o /home/site/wwwroot


# To enable ssh & remote debugging on app service change the base image to the one below
FROM mcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0

ENV AzureWebJobsScriptRoot=/home/site/wwwroot \
    AzureFunctionsJobHost__Logging__Console__IsEnabled=true

EXPOSE $TARGET_PORT

COPY --from=installer-env ["/home/site/wwwroot", "/home/site/wwwroot"]

STEP3: Upload Image to Azure Registry

The following shows how to upload an image to Azure Registry

TOKEN=$(az acr login --name ${ACR_NAME}  --expose-token --output tsv --query accessToken)

docker login ${ACR_NAME}.azurecr.io --username 00000000-0000-0000-0000-000000000000 --password ${TOKEN}

docker push $REMOTE_IMAGE

Docker File

We can create a script below to build and deploy Container App for Azure Function

// DockerFile

#!/usr/bin/env bash


TS=$(date +"%Y%m%d%H%M%S")
# You ACR Name
ACR_NAME="api_server_image"
REMOTE_IMAGE="${ACR_NAME}.azurecr.io/api-service:${TS}"
TARGET_PORT=80
AZURE_USERNAME="<Your User Name>"
AZURE_PASSWORD="<Your Password>"
AZURE_SUBSCRIPTION="<Your Subscription Name>"

BUILD_RUN_TIME="linux-x64"

echo "## Log in Azure ##"
# Manually log in with MFA
az login

# Connect to Subscription
az account set -s "$AZURE_SUBSCRIPTION"


echo "==========================================================================================="
echo "Use $REMOTE_IMAGE as docker image "
echo "TARGET_PORT $TARGET_PORT"
echo "ACR_NAME $ACR_NAME"
echo "==========================================================================================="


if [[ -d "api_server_image" ]]
then
    rm -rf api_server_image
fi

mkdir api_server_image

cp -rf <Your Project>/* api_server_image/
rm -rf api_server_image/bin
rm -rf api_server_image/obj

cd api_server_image

docker build --no-cache -t $REMOTE_IMAGE -f- . <<EOF
FROM mcr.microsoft.com/dotnet/sdk:8.0.401-alpine3.20 AS installer-env

RUN mkdir /app
WORKDIR /app

COPY . .

# Restore the dependencies (NuGet packages)
RUN dotnet restore "./<Your Project>.csproj"

# Build and publish the application to the /app directory
RUN dotnet publish "./<Your Project>.csproj" -c Debug -r $BUILD_RUN_TIME -o /home/site/wwwroot


# To enable ssh & remote debugging on app service change the base image to the one below
FROM mcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0

ENV AzureWebJobsScriptRoot=/home/site/wwwroot \
    AzureFunctionsJobHost__Logging__Console__IsEnabled=true

EXPOSE $TARGET_PORT

COPY --from=installer-env /app/local.settings.json /home/site/wwwroot/
COPY --from=installer-env ["/home/site/wwwroot", "/home/site/wwwroot"]

EOF


TOKEN=$(az acr login --name ${ACR_NAME}  --expose-token --output tsv --query accessToken)

docker login ${ACR_NAME}.azurecr.io --username 00000000-0000-0000-0000-000000000000 --password ${TOKEN}

docker push $REMOTE_IMAGE

Conclusion

In this post, you have learned how to build a scalable C# web application for deploying to Azure Function in Container App.

You don’t need to type magic prompt to try and error for finding a workable Docker file.

This article will be helpful for you to save time for building a high performance and scalable C# web application for Azure Container apps in Azure Function.

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