# net-base

Base  docker file that allows you to deploy .NET wit ease.
Microsoft makes some images available to deploy .NET applications in Docker.
However in order to use them, there is need for some tweaking.

This image is based on the *mcr.microsoft.com/dotnet/aspnet* image, but includes these tweaks.
Among other things these tweaks are included :
 - automatic generation of certificate for the web server
 - disable telemetry
 - inclusion of tzdata for time setup


 ## Docker image

### Environment Variables

| Variable                                            | Description                                                             | Default                                                                                      |
|-----------------------------------------------------|-------------------------------------------------------------------------|----------------------------------------------------------------------------------------------|
| ASPNETCORE_Kestrel__Certificates__Default__Path     | The path containing the server certificate                              | /usr/local/share/ca-certificates/aspnetapp.crt                                               |
| ASPNETCORE_Kestrel__Certificates__Default__KeyPath  | The path containing the key for the server certificate                  | /usr/local/share/ca-certificates/aspnetapp.key                                               |
| ASPNETCORE_Kestrel__Certificates__Default__Password | The password for required for the server key                            | N/A (generated at build time)                                                                |
| CERTIFICATES_DIRECTORY                              | The directory where the certificate files are stored for the web server | /usr/local/share/ca-certificates                                                             |
| ASPNETCORE_URLS                                     | Specifies at which urls and ports the Kestrel server should listen      | http://+:80;https://+:443                                                                    |
| DOTNET_CLI_TELEMETRY_OPTOUT                         | Disables telemetry                                                      | 1                                                                                            |
| TZ                                                  | Time zone ([list](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones#List)) | Europe/Brussels |                                                                               |

### Usage

Since this is just a base image, some additional setup is needed.
The following is just an example of how your Dockerfile could look like.

```sh
# Password for the certificate
# this image contains the entire .NET SDK and is ideal for creation the build
FROM mcr.microsoft.com/dotnet/sdk:8.0-alpine-amd64 AS build-env
WORKDIR /App
COPY . ./
# Restore dependencies for your application
RUN dotnet restore
# Build your application
RUN dotnet publish test.csproj --no-restore --self-contained false -c Release -o out /p:UseAppHost=false 

FROM git.claeyscloud.com/david/net-base:latest
WORKDIR /App
# copy build files from build-stage
COPY --from=build-env /App/out .
# entrypoint for image
ENTRYPOINT ["dotnet", "test.dll"]
```

### Security implications

This images uses the system provided by Microsoft to generate a development certificate and uses the [Kestrel](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/servers/?view=aspnetcore-9.0&tabs=windows) webserver.
In previous .NET versions it was not recommended to expose Kestrel directly to the internet, now Microsoft claims you can do that if you want so.
However you never should use the included development certificate included in this image when doing so.

If you want to expose the Kestrel server you should use the **ASPNETCORE_Kestrel__Certificates__Default__Path**, **ASPNETCORE_Kestrel__Certificates__Default__KeyPath** and **ASPNETCORE_Kestrel__Certificates__Default__Password** variables to correclty setup a certificate. The _dotnet dev-certs_ command is not really suited for production environments.

In practice it's much easier to expose the server through a proxy to the public (hence the recommended method). 
Depending on your use-case you event might consider to use docker networking in order to accomplish proper isolation.