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Vasyl
Vasyl

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Build and Push .NET 8 Apps as Docker Images (No Dockerfile)

1. Why do this?

  • .NET 8 can build a Docker image for you.
  • One command creates and tags the image.
  • You can push the image without Docker on the build server.

2. What you need

  • .NET SDK 8.0.200+ — Build and publish the image.
  • Docker or Podman (optional) — Run the image on your PC.
  • GitHub or Azure DevOps — Run CI/CD examples.

3. Build and run on your PC

Open a terminal and run:

dotnet new console -o MyApp
cd MyApp
dotnet publish -t:PublishContainer -p:EnableSdkContainerSupport=true
docker run --rm myapp:latest
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The SDK picks the base image, tags it myapp:latest, and stores it locally.

4. Change image settings

  • Use Alpine Linux 
  dotnet publish --os linux-musl -t:PublishContainer
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  • Use Ubuntu 22.04 
  dotnet publish -t:PublishContainer -p:ContainerFamily=jammy
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  • Tiny chiseled image 
  dotnet publish -t:PublishContainer -p:ContainerFamily=jammy-chiseled-extra
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  • Set repo & tag 
  dotnet publish -t:PublishContainer -p:ContainerRepository=ghcr.io/user/app -p:ContainerImageTags=v1
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  • Push in build 
  dotnet publish -t:PublishContainer -p:ContainerRegistry=ghcr.io -p:ContainerPush=true
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5. GitHub Actions

Save this as .github/workflows/docker.yml:

name: Build and push image
on: [push]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-dotnet@v4
        with:
          dotnet-version: 8.0.x
      - uses: docker/login-action@v3
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}
      - name: Publish image
        run: |
          dotnet publish -c Release -t:PublishContainer \
            -p:ContainerRepository=ghcr.io/${{ github.repository }} \
            -p:ContainerImageTags=${{ github.sha }} \
            -p:ContainerPush=true
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6. Azure DevOps

Save this as azure-pipelines.yml:

trigger:
- main

pool:
  vmImage: ubuntu-latest

variables:
  acrName: myacr.azurecr.io
  imageRepo: demo/myapp

steps:
- checkout: self
- task: UseDotNet@2
  inputs:
    packageType: sdk
    version: 8.0.x
- script: |
    dotnet publish -c Release -t:PublishContainer \
      -p:ContainerRegistry=$(acrName) \
      -p:ContainerRepository=$(imageRepo) \
      -p:ContainerImageTags=$(Build.BuildNumber) \
      -p:ContainerPush=true
  displayName: Build and push
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7. Quick fixes

  • Hidden folders like .well-known are missing → Rename the folder or add a custom MSBuild target.
  • Need apt packages → Make your own base image and set ContainerBaseImage.
  • Private NuGet feed → Use the same NuGet auth you use in normal builds.

8. Remember

  • No Dockerfile for most apps.
  • Images are smaller and run as non‑root.
  • One command can build and push.

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