All 16 Docker & Containerization questions
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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 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? How does .NET's runtime automatically size the ThreadPool and GC based on container CPU limits, and what issue can arise with fractional CPU limits? What is .NET Aspire, and how does it improve the local development and orchestration experience for cloud-native, multi-service .NET applications?
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.NET › Docker & Containerization

How do you pass environment-specific configuration into a running .NET container, and how does this interact with the configuration system?

Intermediate

Answer

Environment variables passed to a container (via `docker run -e`, a Docker Compose environment section, or a Kubernetes deployment's env field) are automatically picked up by ASP.NET Core's environment variable configuration provider using the double-underscore convention for nested keys, letting you fully configure a container's behavior at deploy time without rebuilding the image or baking environment-specific settings into it.
docker run -e ConnectionStrings__Db="Server=prod-db;..." -e ASPNETCORE_ENVIRONMENT=Production myapp:latest

# Or in Kubernetes:
env:
  - name: ConnectionStrings__Db
    valueFrom: { secretKeyRef: { name: db-secret, key: connection-string } }
Real-world example The exact same Docker image is deployed to dev, staging, and production Kubernetes clusters, with each environment's specific connection strings and feature flags injected purely through environment variables, honoring the 'build once, deploy everywhere' principle.

Common follow-ups: How do you handle secrets specifically (versus regular config) in a Kubernetes environment variable setup?;What ASPNETCORE_ENVIRONMENT value should each deployment tier use?

Configuration & Options;Secrets Management & Configuration Providers (Key Vault User Secrets)
All 16 Docker & Containerization questions