Building .NET 7 Applications with AWS CodeBuild

AWS CodeBuild is a fully managed DevOps service for building and testing your applications. As a fully managed service, there is no infrastructure to manage and you pay only for the resources that you use when you are building your applications. CodeBuild provides a default build image that contains the current Long Term Support (LTS) version of the .NET SDK.

Microsoft released the latest version of .NET in November. This release, .NET 7, includes performance improvements and functionality, such as native ahead of time compilation. (Native AoT)..NET 7 is a Standard Term Support release of the .NET SDK. At this point CodeBuild’s default image does not support .NET 7. For customers that want to start using.NET 7 right away in their applications, CodeBuild provides two means of customizing your build environment so that you can take advantage of .NET 7.

The first option for customizing your build environment is to provide CodeBuild with a container image you create and maintain. With this method, customers can define the build environment exactly as they need by including any SDKs, runtimes, and tools in the container image. However, this approach requires customers to maintain the build environment themselves, including patching and updating the tools. This approach will not be covered in this blog post.

A second means of customizing your build environment is by using the install phase of the buildspec file. This method uses the default CodeBuild image, and adds additional functionality at the point that a build starts. This has the advantage that customers do not have the overhead of patching and maintaining the build image.

Complete documentation on the syntax of the buildspec file can be found here:

https://docs.aws.amazon.com/codebuild/latest/userguide/build-spec-ref.html

Your application’s buildspec.yml file contains all of the commands necessary to build your application and prepare it for deployment. For a typical .NET application, the buildspec file will look like this:

```
version: 0.2
phases:
  build:
    commands:
      - dotnet restore Net7TestApp.sln
      - dotnet build Net7TestApp.sln
```

Note: This build spec file contains only the commands to build the application, commands for packaging and storing build artifacts have been omitted for brevity.

In order to add the .NET 7 SDK to CodeBuild so that we can build your .NET 7 applications, we will leverage the install phase of the buildspec file. The install phase allows you to install any third-party libraries or SDKs prior to beginning your actual build.

```
  install:
    commands:
      - curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin --channel STS 
```

The above command downloads the Microsoft install script for .NET and uses that script to download and install the latest version of the .NET SDK, from the Standard Term Support channel. This script will download files and set environment variables within the containerized build environment. You can use this same command to automatically pull the latest Long Term Support version of the .NET SDK by changing the command argument STS to LTS.

Your updated buildspec file will look like this:

```
version: 0.2    
phases:
  install:
    commands:
      - curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin --channel STS 
  build:
    commands:
      - dotnet restore Net7TestApp/Net7TestApp.sln
      - dotnet build Net7TestApp/Net7TestApp.sln
```

Once you check in your buildspec file, you can start a build via the CodeBuild console, and your .NET application will be built using the .NET 7 SDK.

As your build runs you will see output similar to this:

 ```
Welcome to .NET 7.0! 
--------------------- 
SDK Version: 7.0.100 
Telemetry 
--------- 
The .NET tools collect usage data in order to help us improve your experience. It is collected by Microsoft and shared with the community. You can opt-out of telemetry by setting the DOTNET_CLI_TELEMETRY_OPTOUT environment variable to '1' or 'true' using your favorite shell. 

Read more about .NET CLI Tools telemetry: https://aka.ms/dotnet-cli-telemetry 
---------------- 
Installed an ASP.NET Core HTTPS development certificate. 
To trust the certificate run 'dotnet dev-certs https --trust' (Windows and macOS only). 
Learn about HTTPS: https://aka.ms/dotnet-https 
---------------- 
Write your first app: https://aka.ms/dotnet-hello-world 
Find out what's new: https://aka.ms/dotnet-whats-new 
Explore documentation: https://aka.ms/dotnet-docs 
Report issues and find source on GitHub: https://github.com/dotnet/core 
Use 'dotnet --help' to see available commands or visit: https://aka.ms/dotnet-cli 
-------------------------------------------------------------------------------------- 
Determining projects to restore... 
Restored /codebuild/output/src095190443/src/git-codecommit.us-east-2.amazonaws.com/v1/repos/net7test/Net7TestApp/Net7TestApp/Net7TestApp.csproj (in 586 ms). 
[Container] 2022/11/18 14:55:08 Running command dotnet build Net7TestApp/Net7TestApp.sln 
MSBuild version 17.4.0+18d5aef85 for .NET 
Determining projects to restore... 
All projects are up-to-date for restore. 
Net7TestApp -> /codebuild/output/src095190443/src/git-codecommit.us-east-2.amazonaws.com/v1/repos/net7test/Net7TestApp/Net7TestApp/bin/Debug/net7.0/Net7TestApp.dll 
Build succeeded. 
0 Warning(s) 
0 Error(s) 
Time Elapsed 00:00:04.63 
[Container] 2022/11/18 14:55:13 Phase complete: BUILD State: SUCCEEDED 
[Container] 2022/11/18 14:55:13 Phase context status code: Message: 
[Container] 2022/11/18 14:55:13 Entering phase POST_BUILD 
[Container] 2022/11/18 14:55:13 Phase complete: POST_BUILD State: SUCCEEDED 
[Container] 2022/11/18 14:55:13 Phase context status code: Message:
```

Conclusion

Adding .NET 7 support to AWS CodeBuild is easily accomplished by adding a single line to your application’s buildspec.yml file, stored alongside your application source code. This change allows you to keep up to date with the latest versions of .NET while still taking advantage of the managed runtime provided by the CodeBuild service.

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