Dockerfile-layout

FROM — specifies the base (parent) image.

LABEL —provides metadata. Good place to include maintainer info.

ENV — sets a persistent environment variable.

RUN —runs a command and creates an image layer. Used to install packages into containers.

COPY — copies files and directories to the container.

ADD — copies files and directories to the container. Can upack local .tar files.

CMD — provides a command and arguments for an executing container. Parameters can be overridden. There can be only one CMD.

WORKDIR — sets the working directory for the instructions that follow.

ARG — defines a variable to pass to Docker at build-time.

ENTRYPOINT — provides command and arguments for an executing container. Arguments persist. 

EXPOSE — exposes a port.

VOLUME — creates a directory mount point to access and store persistent data.