What is a Dockerfile and how do you create a Docker image?

A Dockerfile is a text recipe of instructions — starting from a base image — that docker build runs to produce a container image.

* A Dockerfile's instructions plus its base image are combined by docker build into your own runnable image. *

FROM node:24.0.2-alpine3.20

COPY src/ ./
RUN npm install
CMD [ "node", "server.js" ]

Key instructions:

• FROM - base image to start from
• COPY - copy files into the image
• RUN - execute commands during build
• CMD - command to run when container starts

Build the image:

$ docker build -t myapp:latest .

Go deeper:

• Dockerfile reference (Docker docs) — every instruction (FROM, COPY, RUN, CMD, …) you can put in the recipe.