Dockerfile cheatsheet

FROM ruby:2.2.2

ENV APP_HOME /myapp
RUN mkdir $APP_HOME

ARG APP_HOME=""
RUN mkdir $APP_HOME

RUN bundle install

WORKDIR /myapp

VOLUME ["/data"]
# Specification for mount point

ADD file.xyz /file.xyz
COPY --chown=user:group host_file.xyz /path/container_file.xyz

ENV my_var
SHELL ["/bin/bash", "-euo", "pipefail", "-c"]

# With strict mode:
RUN false # fails build like using &&
RUN echo "$myvar" # will throw error due to typo
RUN true | false # will bail out of pipe

Using shell will turn on strict mode for shell commands.

ONBUILD RUN bundle install
# when used with another file

EXPOSE 5900
CMD    ["bundle", "exec", "rails", "server"]

ENTRYPOINT ["executable", "param1", "param2"]
ENTRYPOINT command param1 param2

Configures a container that will run as an executable.

ENTRYPOINT exec top -b

This will use shell processing to substitute shell variables, and will ignore any CMD or docker run command line arguments.

LABEL version="1.0"

LABEL "com.example.vendor"="ACME Incorporated"
LABEL com.example.label-with-value="foo"

LABEL description="This text illustrates \
that label-values can span multiple lines."