In my previous post, I discussed different containerising options for .NET developers. Now, let's slightly move the focus to Azure Functions app. How can you containerise the Azure Functions app? Fortunately, Azure Functions Core Tools natively support it with Dockerfile
. But is the Dockerfile
the only option for containerising your .NET-based Azure Functions apps? Throughout this post, I'm going to discuss how Azure Functions apps can be containerised both with and without Dockerfile
.
You can find a sample code from:
devkimchi / msbuild-for-functions-on-containers
This provides sample .NET function apps using container images with Dockerfile and with MSBuild on Docker Desktop.
MSBuild for Azure Functions on Containers
As a .NET developer, when you build a container image for your Azure Functions app, you can use the
Dockerfile
to define the container image. However, you can also use thedotnet publish
command to build and publish the container image without aDockerfile
. This repository provides sample .NET function apps using container images withDockerfile
and withdotnet publish
.Prerequisites
- .NET SDK 8.0+ with .NET Aspire workload
- Visual Studio or Visual Studio Code + C# Dev Kit + Azure Functions
- Azure Functions Core Tools
- Docker Desktop
Getting Started
NOTE: Make sure Docker Desktop is running before you start.
Run with
Dockerfile
Run
func init
to create a new Azure Functions app with Docker support.func init FunctionAppWithDockerfile --worker-runtime dotnet-isolated --docker --target-framework net8.0Confirm the
Dockerfile
is created in theFunctionAppWithDockerfile
folder.Run
func new
to add a new HTTP trigger…
Prerequisites
There are a few prerequisites to containerise .NET-based function apps effectively.
- .NET SDK 8.0+
- Azure Functions Core Tools
- Visual Studio or Visual Studio Code + C# Dev Kit + Azure Functions
- Docker Desktop
Containerise with Dockerfile
With the Azure Functions Core Tools, you can create a new Azure Functions app with the following command:
func init FunctionAppWithDockerfile \
--worker-runtime dotnet-isolated \
--docker \
--target-framework net8.0
You may notice the --docker
option in the command. This option creates a Dockerfile
in the project directory. The Dockerfile
looks like this:
FROM mcr.microsoft.com/dotnet/sdk:8.0 AS installer-env
COPY . /src/dotnet-function-app
RUN cd /src/dotnet-function-app && \
mkdir -p /home/site/wwwroot && \
dotnet publish *.csproj --output /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-appservice
FROM mcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0
ENV AzureWebJobsScriptRoot=/home/site/wwwroot \
AzureFunctionsJobHost__Logging__Console__IsEnabled=true
COPY --from=installer-env ["/home/site/wwwroot", "/home/site/wwwroot"]
There are a few points on Dockerfile
to pick up:
- The base image for the runtime is
mcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0
. There are two other options available,mcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0-slim
andmcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0-mariner
. You can choose one of them based on your requirements. - The function app is running on the
/home/site/wwwroot
directory. - It has two environment variables,
AzureWebJobsScriptRoot
andAzureFunctionsJobHost__Logging__Console__IsEnabled
. - There's no
ENTRYPOINT
instruction defined.
These points will be used later on this post.
Let's add a new function to the Azure Functions app with the following command:
func new -n HttpExampleTrigger -t HttpTrigger -a anonymous
Once it's added, open the HttpExampleTrigger.cs
file and modify it as follows:
// Before
return new OkObjectResult("Welcome to Azure Functions!");
// After
return new OkObjectResult("Welcome to Azure Functions with Dockerfile!");
Now, you can build the container image with the following command:
docker build . -t funcapp:latest-dockerfile
You have the container image for the Azure Functions app. You can run the container with the following command:
docker run -d -p 7071:80 --name funcappdockerfile funcapp:latest-dockerfile
Your function app is now up and running in a container. Open the browser and navigate to http://localhost:7071/api/HttpExampleTrigger
to see the function app running.
Open your Docker Desktop and check the running container.
Can you see the Path
and Args
value? The Path
value is /opt/startup/start_nonappservice.sh
and the Args
value is an empty array. In other words, the shell script, start_nonappservice.sh
is executed when the container starts, and it takes no arguments. Keep this information in mind. You'll use it later in this post.
Once you're done, stop and remove the container with the following commands:
docker stop funcappdockerfile && docker rm funcappdockerfile
So far, we've containerised the Azure Functions app with the Dockerfile
. But, as I mentioned before, there is another way to containerise the Azure Functions app without having Dockerfile
. Let's move on.
Containerise with dotnet publish
Because MSBuild natively supports containerisation, you can make use of the dotnet publish
command to build the container image for your function app. If you want to dynamically set the base container image, this option will be really useful. To do this, you might need to update your .csproj
file to include the containerisation settings. First of all, create a new function app without the --docker
option.
func init FunctionAppWithMSBuild \
--worker-runtime dotnet-isolated \
--target-framework net8.0
Let's add a new function to the Azure Functions app with the following command:
func new -n HttpExampleTrigger -t HttpTrigger -a anonymous
Once it's added, open the HttpExampleTrigger.cs
file and modify it as follows:
// Before
return new OkObjectResult("Welcome to Azure Functions!");
// After
return new OkObjectResult("Welcome to Azure Functions with MSBuild!");
Now, the fun part begins. Open the FunctionAppWithMSBuild.csproj
file and add the following node:
<ItemGroup>
<ContainerEnvironmentVariable
Include="AzureWebJobsScriptRoot" Value="/home/site/wwwroot" />
<ContainerEnvironmentVariable
Include="AzureFunctionsJobHost__Logging__Console__IsEnabled" Value="true" />
</ItemGroup>
Did you find that these two environment variables are the same as the ones in the Dockerfile
? Let's add another node to the .csproj
file:
<ItemGroup Label="ContainerAppCommand Assignment">
<ContainerAppCommand Include="/opt/startup/start_nonappservice.sh" />
</ItemGroup>
This node specifies the command to run when the container starts. This is the same as the Path
value in the Docker Desktop
screenshot. Now, you can build the container image with the following command:
dotnet publish ./FunctionAppWithMSBuild \
-t:PublishContainer \
--os linux --arch x64 \
-p:ContainerBaseImage=mcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0 \
-p:ContainerRepository=funcapp \
-p:ContainerImageTag=latest-msbuild \
-p:ContainerWorkingDirectory="/home/site/wwwroot"
NOTE: You can set the base container image with
mcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0-slim
ormcr.microsoft.com/azure-functions/dotnet-isolated:4-dotnet-isolated8.0-mariner
, depending on your requirements.
This command takes four properties – ContainerBaseImage
, ContainerRepository
, ContainerImageTag
, and ContainerWorkingDirectory
. With this dotnet publish
command, you have the same development experience as building the container image with the docker build
command, without having to rely on Dockerfile
.
Run the following command to run the container:
docker run -d -p 7071:80 --name funcappmsbuild funcapp:latest-msbuild
Your function app is now up and running in a container. Open the browser and navigate to http://localhost:7071/api/HttpExampleTrigger
to see the function app running.
Open your Docker Desktop and check the running container.
Can you see the Path
and Args
value? The Path
value is /opt/startup/start_nonappservice.sh
and the Args
value has dotnet
and FunctionAppWithMSBuild.dll
. But these arguments are ignored because the shell script doesn't take any argument.
Once you're done, stop and remove the container with the following commands:
docker stop funcappmsbuild && docker rm funcappmsbuild
Now, you've got the Azure Functions app containerised without Dockerfile
. With this dotnet publish
approach, you can easily change the base container image, repository, tag, and working directory without relying on Dockerfile
.
So far, I've walked through how .NET developers can containerise their .NET-based Azure Functions apps with two different options. You can either write Dockerfile
s or use dotnet publish
to build container images. Which one do you prefer?
More about MSBuild for Containers?
If you want to learn more options about containers with MSBuild, the following links might be helpful.
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