What instructions must be present in a Dockerfile for correct container building?

The following instructions must be present in a Dockerfile for correct container assembly:

• FROM — specifies the base image from which your container will be built.
• COPY or ADD — for copying files from the build context into the container.
• RUN — for executing commands during the build (e.g., installing dependencies).
• CMD or ENTRYPOINT — define the command that will run when the container starts.

Example of a minimal Dockerfile:

FROM ubuntu:20.04
COPY app.sh /app.sh
RUN chmod +x /app.sh
CMD ["/app.sh"]