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Docker Tip #46: Using WORKDIR to Cleanup Your Dockerfile

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If you find yourself frequently changing directories in your Dockerfile then you may want to look into using WORKDIR. Here's how.

The WORKDIR instruction allows you to set a specific path in one spot, and then most instructions (RUN and COPY to name a few) will execute in the context of that WORKDIR.

Let’s say this were your old Dockerfile that didn’t use WORKDIR:
FROM python:2.7-alpine

RUN mkdir /app

COPY requirements.txt /app/requirements.txt
RUN cd /app && pip install -r requirements.txt

COPY . /app

CMD /app/gunicorn -b 0.0.0.0:8000 --access-logfile - "foo.app:create_app()"

Yikes, you had to repeat the /app path in so many spots.

You can drastically improve the above Dockerfile by leveraging WORKDIR:
FROM python:2.7-alpine

# We don't even need to run mkdir /app since WORKDIR will make it for us.
WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt

COPY . .

CMD gunicorn -b 0.0.0.0:8000 --access-logfile - "foo.app:create_app()"

The key there is setting WORKDIR /app. Everything after that point will execute from the /app directory.

You can think of it as doing a cd but the directory you change into will persist between instructions. You can even have more than 1 WORKDIR in your Dockerfile if you need it.

Here’s an example of using multiple WORKDIRs:
WORKDIR /foo/bar
WORKDIR baz

RUN pwd

The above pwd command would resolve to /foo/bar/baz.

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