Provide distroless base image for dotnet core runtime dependencies.

[TonyDou]

The benefits of distroless base image for dotnet core is mainly for security.

1. Well known base images introduce lots of unused binaries which may introduce security vulnerabilities.
2. The distroless base image could only contain the minimum number of native binaries that's not linked or packaged by dotnet publish. And this base image will be very tiny in size.
3. You can also consider to release another distroless image with dotnet core runtime built in.

[MichaelSimons]

@TonyDou - Can you explain the usage scenarios in which a distroless base image would be advantageous over using the Alpine based .NET image? Alpine is our smallest and most secure offering.

[MichaelSimons]

@TonyDou - Can you share your usage scenario?

[TonyDou]

Hi @MichaelSimons It's true that Alpine is already very small but it also contains binaries like sh that's not referenced or used by dotnet runtime. The request is more about security concerns not about image size. If we remove binaries in base image as much as possible, the potential security vulnerabilities will be fewer.

[yshahin]

One is already provided by distroless repo
https://console.cloud.google.com/gcr/images/distroless/GLOBAL/dotnet/core/aspnet?gcrImageListsize=30

It would be better if the dotnet team maintains this so that we get the latest dotnet as well as the correct dependences for all features.

[MichaelSimons]

We've heard a couple requests for this but not a significant amount. Adding support for distroless images is a significant cost because it requires adopting a new tool chain. It is more work than adding images for an already supported distro.

We would like to hear from others who would find this useful and what their motivations are. We will close this issue in 30 days if we do not hear from a substantial number of users.

[yshahin]

Also I would like to add that since we only have the essential so's, the rate of scanning alerts reduce a lot.
We don't need to use distroless, if you create a dotnet image from docker scratch image, you would get the same benefits.

[MichaelSimons]

Closing per the 30 day comment I made earlier. If you would find distroless images useful, please continue to share your scenario/comments.

[ctstone]

An important distinction of distroless from Alpine is the availability of glibc (when using distroless/cc) for applications that use native libraries that expect to find debian libs. Alpine uses musl which is only partially compatible with glibc. In my experience this usually leads to recompiling from source which can be tricky if there are complex dependencies.

[aw185176]

Alpine also has known DNS issues in K8s environments: https://stackoverflow.com/questions/65181012/does-alpine-have-known-dns-issue-within-kubernetes

[torjue]

Ended up with something like this:

Runtime image:

# Use alpine to gather all dependencies
FROM alpine:3.14 as base

RUN apk add --no-cache  icu-libs \
                        krb5-libs \
                        libgcc \
                        libintl \
                        libssl1.1 \
                        libstdc++ \
                        zlib \
                        ca-certificates && update-ca-certificates

# Cleanup /lib
RUN find /lib -type d -empty -delete && \
    rm -r /lib/apk && \
    rm -r /lib/sysctl.d

# Create runtime image
FROM scratch
COPY --from=base /lib/ /lib
COPY --from=base /usr/lib /usr/lib
COPY --from=base /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt

# chmod hack: extract tmp.tar file with correct flags
# see https://github.com/GoogleContainerTools/distroless/blob/main/base/tmp.tar
ADD tmp.tar .

ENV ASPNETCORE_URLS=http://+:80 \
    DOTNET_RUNNING_IN_CONTAINER=true \
    DOTNET_SYSTEM_GLOBALIZATION_INVARIANT=true

Usage:

# Build as self contained executable
FROM mcr.microsoft.com/dotnet/sdk:5.0-alpine AS build
WORKDIR /source

COPY app/*.csproj .
RUN dotnet restore -r linux-musl-x64

COPY app/. .
RUN dotnet publish \
        -c release \
        -o /app \
        -r linux-musl-x64 \
        --self-contained true \
        --no-restore \
        /p:PublishTrimmed=true \
        /p:PublishSingleFile=true \
        /p:LinkMode=trim \
        /p:DebugType=None \
        /p:DebugSymbols=false

# final stage
FROM dotnet-superslim
WORKDIR /app
COPY --from=build --chown=1111:1111 /app ./
USER 1111
ENTRYPOINT ["./app"]

[torjue]

Came across #3141, so there might be some movement on this?

[mthalman]

@torjue - We're interested in distroless and exploring that space. And yes, #3141 is an implementation of that but just for CBL-Mariner.

Your sample shows Alpine being used and there's recently been some tooling prototype developed for Alpine to enable distroless support. I've done a prototype on top of that for .NET and it yielded good results.

Distroless is definitely on our radar but we have no concrete plans for it other than #3141.