I'm learning Docker. For many times I've seen that Dockerfile has WORKDIR command:
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” ]
Can't I just omit WORKDIR and Copy and just have my Dockerfile at the root of my project? What are the downsides of using this approach?
According to the documentation:
The WORKDIR instruction sets the working directory for any RUN, CMD, ENTRYPOINT, COPY and ADD instructions that follow it in the Dockerfile. If the WORKDIR doesn’t exist, it will be created even if it’s not used in any subsequent Dockerfile instruction.
Also, in the Docker best practices it recommends you to use it:
... you should use WORKDIR instead of proliferating instructions like RUN cd … && do-something, which are hard to read, troubleshoot, and maintain.
I would suggest to keep it.
I think you can refactor your Dockerfile to something like:
FROM node:latest
WORKDIR /usr/src/app
COPY package.json .
RUN npm install
COPY . ./
EXPOSE 3000
CMD [ "npm", "start" ]
You dont have to
RUN mkdir -p /usr/src/app
This will be created automatically when you specifiy your WORKDIR
FROM node:latest
WORKDIR /usr/src/app
COPY package.json .
RUN npm install
COPY . ./
EXPOSE 3000
CMD [ “npm”, “start” ]
You can think of WORKDIR like a cd inside the container (it affects commands that come later in the Dockerfile, like the RUN command). If you removed WORKDIR in your example above, RUN npm install wouldn't work because you would not be in the /usr/src/app directory inside your container.
I don't see how this would be related to where you put your Dockerfile (since your Dockerfile location on the host machine has nothing to do with the pwd inside the container). You can put the Dockerfile wherever you'd like in your project. However, the first argument to COPY is a relative path, so if you move your Dockerfile you may need to update those COPY commands.