Document Skill original
Rendu depuis le dépôt source en conservant titres, exemples, code, tableaux, liens et images.
Docker
Core Principles
- Multi-stage builds always — Separate build and runtime stages. Build in the SDK image, run in the ASP.NET runtime image.
- Non-root by default — .NET container images support
USER appby default since .NET 8. Never run as root in production. - Layer caching matters — Copy
.csprojfiles and restore before copying source code. This caches NuGet dependencies across builds. - Health probes at the orchestrator level — Expose a
/health/liveendpoint and let Kubernetes/Compose probe it. Chiseled and default aspnet images have no shell or curl, so in-imageHEALTHCHECKcommands have nothing to run with.
Patterns
Multi-Stage Dockerfile for Web API
dockerfile
# Stage 1: Build
FROM mcr.microsoft.com/dotnet/sdk:10.0 AS build
WORKDIR /src
# Copy project files and restore (cached layer)
COPY ["src/MyApp.Api/MyApp.Api.csproj", "src/MyApp.Api/"]
COPY ["src/MyApp.Domain/MyApp.Domain.csproj", "src/MyApp.Domain/"]
COPY ["Directory.Build.props", "."]
COPY ["Directory.Packages.props", "."]
RUN dotnet restore "src/MyApp.Api/MyApp.Api.csproj"
# Copy everything and build
COPY . .
RUN dotnet publish "src/MyApp.Api/MyApp.Api.csproj" \
-c Release \
-o /app/publish \
--no-restore
# Stage 2: Runtime
FROM mcr.microsoft.com/dotnet/aspnet:10.0 AS runtime
WORKDIR /app
# Non-root user (default in .NET 8+ images)
USER app
COPY --from=build /app/publish .
EXPOSE 8080
ENTRYPOINT ["dotnet", "MyApp.Api.dll"]Container Health Probes
Prefer orchestrator-level probes (Kubernetes livenessProbe, Compose healthcheck) over a Dockerfile HEALTHCHECK — the standard aspnet and chiseled images ship no shell, no curl, and no wget, so there is nothing inside the container to run the probe with. Point the orchestrator at /health/live:
yaml
# docker-compose — probe from outside the app process
services:
api:
healthcheck:
test: ["CMD-SHELL", "wget -qO- http://localhost:8080/health/live || exit 1"]
interval: 30s
timeout: 3s
retries: 3
# Note: CMD-SHELL requires a shell + wget in the image. Use a non-chiseled
# variant for this, or better: let Kubernetes httpGet probes do it —
# they run from the kubelet, needing nothing inside the image.If you must have an in-image HEALTHCHECK, base the runtime stage on a non-chiseled image that includes wget — never re-run the app binary as the probe command; that starts a second instance instead of checking the first.
.dockerignore
**/.git
**/.vs
**/bin
**/obj
**/node_modules
**/Dockerfile*
**/docker-compose*
**/testsDocker Compose for Local Development
Key .NET-specific concerns — pass connection strings via environment, use depends_on with health checks:
yaml
services:
api:
build:
context: .
dockerfile: src/MyApp.Api/Dockerfile
ports:
- "5000:8080"
environment:
- ASPNETCORE_ENVIRONMENT=Development
- ConnectionStrings__Default=Host=postgres;Database=myapp;Username=postgres;Password=postgres
- ConnectionStrings__Redis=redis:6379
depends_on:
postgres:
condition: service_healthy
# Add postgres/redis services with healthcheck — standard boilerplateOptimized Build with .slnx
For solutions with multiple projects, restore only the necessary projects.
dockerfile
FROM mcr.microsoft.com/dotnet/sdk:10.0 AS build
WORKDIR /src
# Copy solution and all project files
COPY *.slnx .
COPY Directory.Build.props .
COPY Directory.Packages.props .
COPY src/**/*.csproj ./src/
# Restore project structure
RUN for file in src/**/*.csproj; do \
mkdir -p $(dirname $file) && mv $file $(dirname $file)/; \
done
RUN dotnet restore
COPY . .
RUN dotnet publish src/MyApp.Api -c Release -o /app/publish --no-restoreHealth Check Endpoint
csharp
// In Program.cs — lightweight health endpoint for Docker
app.MapGet("/health/live", () => Results.Ok("healthy"))
.ExcludeFromDescription();Anti-patterns
Don't Use SDK Image for Runtime
dockerfile
# BAD — SDK image is 900MB+, includes compilers
FROM mcr.microsoft.com/dotnet/sdk:10.0
COPY . .
RUN dotnet run
# GOOD — separate build and runtime, runtime image is ~200MB
FROM mcr.microsoft.com/dotnet/aspnet:10.0Don't Copy Everything Before Restore
dockerfile
# BAD — any source change invalidates the NuGet cache
COPY . .
RUN dotnet restore
# GOOD — copy only project files first, then restore
COPY ["src/MyApp.Api/MyApp.Api.csproj", "src/MyApp.Api/"]
RUN dotnet restore "src/MyApp.Api/MyApp.Api.csproj"
COPY . .Don't Run as Root
dockerfile
# BAD — running as root (security risk)
FROM mcr.microsoft.com/dotnet/aspnet:10.0
COPY --from=build /app .
ENTRYPOINT ["dotnet", "MyApp.Api.dll"]
# GOOD — use the built-in non-root user
FROM mcr.microsoft.com/dotnet/aspnet:10.0
USER app
COPY --from=build /app .
ENTRYPOINT ["dotnet", "MyApp.Api.dll"]Decision Guide
| Scenario | Recommendation |
|---|---|
| Web API container | Multi-stage build with aspnet runtime image |
| Worker service | Multi-stage build with dotnet/runtime image |
| Local development | Docker Compose with service dependencies |
| CI builds | Multi-stage build (self-contained) |
| Image size optimization | Use Alpine variant + trimming for small images |
| Health monitoring | /health endpoint + orchestrator probe (K8s httpGet / Compose healthcheck) |
| Secrets | Environment variables or mounted secrets, never in image |
