It's declarative in the sense that the instructions are set in text. But what goes inside a Dockerfile might be imperative, like running apt-get to install packages (i.e., running steps in order).
But what goes inside a Dockerfile might be imperative, like running apt-get to install packages (i.e., running steps in order)
But...that too is done via the Dockerfile, via the RUN command to execute commands inside the container at run time. Or alternatively using the ENTRYPOINT command.
