What would you put in a production Docker image for an ASP.NET Core API, and how would you keep the image small, secure, and repeatable?

Build a production container image for a .NET API

Builds a small, immutable, non-root .NET runtime image with controlled inputs, external configuration, graceful lifecycle behavior, and a practical patching strategy.

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I would use a multi-stage build: restore, build, test, and publish with an SDK image, then copy only the published output into the matching ASP.NET Core runtime image. The final image would run as a non-root user, contain no source code or secrets, and receive environment-specific configuration at runtime. I would tag it with the commit or release identity and deploy that immutable image through every environment. A .dockerignore would keep build output, repository metadata, and local secrets out of the build context.

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Multi-stage builds, SDK and runtime separation, immutable images, non-root execution, configuration, secrets, lifecycle signals, diagnostics, and patching.

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A container image becomes the deployable application boundary. Build choices affect repeatability, startup, patching, diagnostics, and the permissions an attacker receives if the process is compromised.
I would use a multi-stage build: restore, build, test, and publish with an SDK image, then copy only the published output into the matching ASP.NET Core runtime image. The final image would run as a non-root user, contain no source code or secrets, and receive environment-specific configuration at runtime. I would tag it with the commit or release identity and deploy that immutable image through every environment. A .dockerignore would keep build output, repository metadata, and local secrets out of the build context.
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I would make the inputs controlled and the runtime behavior explicit. Package lock files and pinned base-image versions improve repeatability, while build cache layers keep restore efficient. The API writes logs to standard output, exposes separate liveness and readiness behavior, listens on the documented port, and handles termination long enough to stop accepting traffic and finish bounded work. The filesystem can be read-only apart from deliberate temporary paths, and the deployment sets CPU, memory, and process limits rather than relying on the image to discover them.

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Shipping the SDK and build tools in the runtime image.
Copying the entire repository, secrets, or local configuration into the image.
Running as root because the application works locally that way.
Deploying a mutable latest tag with no commit or digest traceability.

What would you put in a production Docker image for an ASP.NET Core API, and how would you keep the image small, secure, and repeatable?

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What would you put in a production Docker image for an ASP.NET Core API, and how would you keep the image small, secure, and repeatable?

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