What is the point of WORKDIR on Dockerfile?

Question

So while learning Docker I saw that WORKDIR & COPY commands were used a lot in the dockerfile like given below:

FROM node:latest
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app
COPY package.json /usr/src/app/
RUN npm install
COPY . /usr/src/app
EXPOSE 3000
CMD [ “npm”, “start” ] 

I just don't get the whole point of using the WORKDIR & COPY commands, I would prefer to just work from the root of my project.

Are there any downsides to this approach?

Answer 1

Let's first see the definition/purpose of both of them :

WORKDIR : This instruction is used to set the working directory in the container.

COPY : This instruction is used to copy any files from the host onto the container.

The reason why these instructions should be used are :

• Using WORKDIR gives clarity and reliability.
•  Using RUN cd … && do-something instructions instead is tougher as they are hard to read & maintain & troubleshoot.

It would be better if you understood these instructions and made proper use of them as these are part of the best docker practices, so keep them in mind. 

Hope this helped :)

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