Name four key directives used in Dockerfile.

Four key directives commonly used in Dockerfile:

1. FROM — specifies the base image from which the new image will be built.
2. RUN — executes commands inside the container during the image build (e.g., installing packages).
3. COPY — copies files or directories from the build context into the image's filesystem.
4. CMD — sets the command to be executed when the container starts (can be overridden).

Example Dockerfile:

FROM node:14
RUN mkdir /app
COPY . /app
CMD ["node", "/app/index.js"]