I have been slowly getting comfortable with Kubernetes after the Docker multi-stage work earlier this year. Mostly YAML, mostly copy-paste from Stack Overflow, mostly “it works on my cluster.” Then 1.16 shipped in September and a few of those manifests started getting rejected with errors that looked like the API server had never heard of extensions/v1beta1.

That is not a bug. For the first time, Kubernetes actually stopped serving a pile of deprecated API versions. If your Deployment still says apiVersion: extensions/v1beta1, 1.16 will not politely convert it for you on the way in. It says no.

I spent part of last weekend trying to containerize a small ASP.NET Core API on my Windows laptop. The first image I produced “worked” — docker run answered on port 5000 — and then I looked at the size. Over a gigabyte for a service that is basically a couple of controllers and EF Core. That is not a deployable unit; that is me shipping the compiler to production by accident.

The fix is not exotic. Multi-stage Docker builds have been around since Docker 17.05, and the .NET team has been pushing the pattern hard as .NET Core 3.0 gets close to GA. Build with the SDK image, run with the ASP.NET runtime image, copy only the published output across. Once you see it, you cannot unsee the single-stage Dockerfile you wrote last month.

This post demonstrate the use of code snippets in the theme. The code snippets are powered by Pygments and the code theme that is been used in Reverie is called Draula.

Sometimes, your post just stands for itself and doesn’t need a title. And that’s fine, too!

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