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What is the difference between an image and a container in Docker terminology, applied to a .NET application? How does a multi-stage Dockerfile reduce the final image size for a .NET application, and what does each stage typically do? How do you configure a .NET container to respect memory and CPU limits set by the container orchestrator (like Kubernetes resource limits)? Why is it recommended to run a containerized .NET application as a non-root user, and how do you configure this in a Dockerfile? What is Docker Compose, and how does it simplify running a multi-container .NET application locally (e.g., API + database + Redis)? How do you pass environment-specific configuration into a running .NET container, and how does this interact with the configuration system? How does .dockerignore improve Docker build performance and image cleanliness for .NET projects? How do you configure a .NET application inside a container to listen on the correct port, and what does ASPNETCORE_URLS control? Why does copying only the .csproj file before the rest of the source code in a Dockerfile improve build caching? What is Native AOT's benefit for containerized .NET applications specifically, beyond the general startup time improvement?
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What are the official .NET Docker base images, and what's the difference between the sdk, aspnet, and runtime image variants?

Beginner

Answer

The sdk image (mcr.microsoft.com/dotnet/sdk) includes the full SDK for building and publishing applications -- large, used only in build stages. The aspnet image (mcr.microsoft.com/dotnet/aspnet) includes the ASP.NET Core runtime for running web applications -- smaller, used as the final production base for web apps. The runtime image (mcr.microsoft.com/dotnet/runtime) includes just the base .NET runtime without ASP.NET Core-specific components, for non-web console/worker applications.
# Building a console app: runtime is sufficient (smaller than aspnet)
FROM mcr.microsoft.com/dotnet/runtime:8.0 AS final

# Building a web API: needs aspnet for Kestrel, MVC, etc.
FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS final
Real-world example A background worker service that processes messages and has no web endpoints uses the smaller dotnet/runtime base image instead of dotnet/aspnet, avoiding unnecessary ASP.NET Core components it will never use.

Common follow-ups: What's the size difference between these base image variants?;What is the runtime-deps image and when would you use it instead?

.NET CLI SDK & Project Structure (csproj);CI/CD Publishing & Deployment
All 16 Docker & Containerization questions