net-base
Base docker image that allows you to deploy .NET APIs with ease.
Microsoft makes some images available to deploy .NET applications in Docker.
However in order to use them succesfully, some additional work is needed.
This image intends to make this task much easier.
This image is based on the mcr.microsoft.com/dotnet/aspnet image, but includes these tweaks. Among other things these tweaks are included :
- automatic certificate generation for the web server
- disable telemetry
- inclusion of tzdata for time setup
Docker image
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.
# Password for the certificate
# this image contains the entire .NET SDK and is ideal for creation the build
FROM mcr.microsoft.com/dotnet/sdk:9.0-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 .
# change ownership of files to the app user
RUN chown -R app:app /App/
# entrypoint for image
ENTRYPOINT ["dotnet", "test.dll"]
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) | Europe/Brussels |
Build arguments
These are the most important build arguments. Most of them are optional, meaning you can tweak them if you so desire. However the CERT_PASSWORD argument is required, as it's necesarry in order to build a working image.
You can build the image yourself like this
docker build --build-arg CERT_PASSWORD=supersecretpassword . -t net-base
| Argument | Description | Default |
|---|---|---|
| CERT_PASSWORD | The password for the generated certificate | N/A (required) |
| DOTNET_SDK_VERSION | The SDK version used to generate the development certificate | 9.0.203 |
| DOTNET_RUNTIME_VERSION | The runtime version used as a base | 9.0.4 |
| ALPINE_VERSION | The version of alpine linux used as a base Currently you can choose between 3.20 or 3.21 |
3.21 |
Security implications
Webserver and certificates
This images uses the system provided by Microsoft to generate a development certificate and uses the Kestrel 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.
The certificate included by default (generated through the dotnet dev-certs command) is not really suited for production environments.
If you want to directly expose the Kestrel webserver use the following environment variables to properly setup a certificate :
- ASPNETCORE_Kestrel__Certificates__Default__Path (the path to the certificate key)
- ASPNETCORE_Kestrel__Certificates__Default__KeyPath (the path to the certificate)
- ASPNETCORE_Kestrel__Certificates__Default__Password (the password for the key file)
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.
Included certificate
The included certificate is generated through the dotnet dev-certs command. This is a very convenient and suitable way to generate development certificates through the dotnet SDK.
The password used to generate the certificate is randomly generated through the openssl rand -base64 12 at build time.
The build agent used for the build is hosted on my own infrastructure but I don't have any access to it (neither do I intend to do so).
However if you feel uncomfortable with this fact, feel free to build the image yourself.
FAQ
What holds the future this project?
This is a project I maintain in my spare time. I don't want to make any empty promises about how much work I'll spend working on it. As some tweaks might be needed for other projects, they might triple down to this one. Although to be completely honest I don't think this project will require much work apart from keeping up with runtime updates.
When will be version xx.xx be available ?
I don't plan to make images available for older versions of the .NET framework. You might be lucky and be able to just tweak the related environment variables and make a build of your own. Regarding the future, I only plan to keep up with stable releases (so no preview versions).