This buildspec.yml file uses the version 0.2 of the buildspec format, which is the latest version at the time of writing. It specifies three phases of the build process: pre_build, build, and post_build.
In the pre_build phase, the dotnet restore command is run to restore the required packages for the application.
In the build phase, the dotnet build command is run to build the application. The --configuration option is set to Release to specify that a release build should be created.
In the post_build phase, the dotnet publish command is run to publish the application and create a deployment package. The --configuration and --output options are set to Release and ./publish, respectively, to specify the configuration and location of the deployment package.
Finally, the artifacts section specifies that the build artifacts should be packaged as a zip file and that the files to be included are those in the publish directory.