In Dockerfile, instructions RUN, CMD, and ENTRYPOINT can contain long shell scripts chaining multiple
commands, including the cd command for changing directories. Using WORKDIR instruction instead reduces the complexity of the
above instructions and makes them easier to read, understand, troubleshoot, and maintain.
What is the potential impact?
The Dockerfile instructions like RUN allow users to execute longer scripts. See the following example:
RUN cd /tmp && \
git clone myrepository.com/MyOrganization/project && \
cd project && \
make && \
cd /app/bin
In this example, the first cd /tmp command can be replaced by WORKDIR /tmp before RUN. The last cd
/app/bin command can be replaced with WORKDIR /app/bin after the RUN instruction. The result will be the
following:
WORKDIR /tmp
RUN git clone myrepository.com/MyOrganization/project && \
cd project && \
make
WORKDIR /app/bin
Those actions will reduce the length of the RUN instruction, which makes it easier to read and understand. Sometimes, it is hard to
avoid the usage of cd command, especially in the middle of a long script. Removing them from the beginning and end of a multi-line is an
easy improvement. Additionally, many commands work well with absolute paths, so changing directories can be avoided in most cases.
The WORKDIR instruction can be used multiple times in a Dockerfile. It changes the current directory for the next instructions and
until there is a following change. This approach simplifies understanding of what is a current directory.
The same principles apply to CMD and ENTRYPOINT instructions.
This recommendation provides a clear structure for Dockerfiles, making it easier to maintain.
