Docker

docker build sends a directory to the Docker daemon, then executes your Dockerfile against it one cached layer at a time.

A VM virtualizes hardware and runs a full kernel per guest. A container shares the host kernel and isolates a process. That one difference explains almost everything else.

Linux runs Docker natively. Mac and Windows run it inside a small Linux VM, which is worth knowing before you chase a ‘missing’ performance number.

There’s no if/else instruction in Dockerfile syntax. Conditional behavior comes from either shell conditionals inside RUN, or picking a different build stage entirely.

A Dockerfile is a build recipe: a short list of instructions that turns a base image and your files into a new image.

The four commands that make up the Docker Hub workflow, and how to decode the ‘denied: requested access’ error.

A tag is a mutable pointer to an image digest. Understanding that one fact explains most tagging mistakes.

A repository is a named bucket of related image versions. Here’s how naming, namespaces and visibility actually work.

A registry is just a content-addressed blob store with an HTTP API in front of it. Here’s how the pieces fit together.