Switch to Azure Linux base image

* Reduces the overall final image size by using Azure Linux
* Offers maximum compatibility with Azure infrastructure
* Uses arbitrary user instead of 'root'

Dockerfile

@@ -1,26 +1,31 @@
-# Stage 1
-ARG ASPNET_IMAGE_TAG=8.0-bookworm-slim
-FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
-WORKDIR /build
+# Set the major version of dotnet
+ARG DOTNET_VERSION=8.0
 
-ENV DEBIAN_FRONTEND=noninteractive
+# Stage 1 - Build the app using the dotnet SDK
+ARG DOTNET_VERSION
+FROM "mcr.microsoft.com/dotnet/sdk:${DOTNET_VERSION}-azurelinux3.0" AS build
+WORKDIR /build
 
 COPY ./Dfe.Academies.External.Web/ ./Dfe.Academies.External.Web/
+COPY ./script/web-docker-entrypoint.sh /app/docker-entrypoint.sh
 
+# Mount GitHub Token as a Docker secret so that NuGet Feed can be accessed
 RUN --mount=type=secret,id=github_token dotnet nuget add source --username USERNAME --password $(cat /run/secrets/github_token) --store-password-in-clear-text --name github "https://nuget.pkg.github.com/DFE-Digital/index.json"
-RUN dotnet restore Dfe.Academies.External.Web
-RUN dotnet build Dfe.Academies.External.Web --no-restore
-RUN dotnet publish Dfe.Academies.External.Web -c Release -o /app --no-restore
 
-COPY ./script/web-docker-entrypoint.sh /app/docker-entrypoint.sh
+# Restore, build and publish the dotnet solution
+RUN ["dotnet", "restore", "Dfe.Academies.External.Web"]
+RUN ["dotnet", "build", "Dfe.Academies.External.Web", "--no-restore"]
+RUN ["dotnet", "publish", "Dfe.Academies.External.Web", "--no-build", "-c", "Release", "-o", "/app"]
 
-# Stage 2
-ARG ASPNET_IMAGE_TAG
-FROM "mcr.microsoft.com/dotnet/aspnet:${ASPNET_IMAGE_TAG}" AS final
-LABEL org.opencontainers.image.source=https://github.com/DFE-Digital/Dfe.Academies.External
+# Stage 2 - Build a runtime environment
+ARG DOTNET_VERSION
+FROM "mcr.microsoft.com/dotnet/aspnet:${DOTNET_VERSION}-azurelinux3.0" AS final
+WORKDIR /app
+LABEL org.opencontainers.image.source="https://github.com/DFE-Digital/Dfe.Academies.External"
 
 COPY --from=build /app /app
-WORKDIR /app
-RUN chmod +x ./docker-entrypoint.sh
+RUN ["chmod", "+x", "./docker-entrypoint.sh"]
+
+USER $APP_UID
 ENV ASPNETCORE_HTTP_PORTS=80
 EXPOSE 80/tcp