WORKDIR Instruction within the Dockerfile

In this tutorial, we will learn how to work with the WORKDIR instruction when using Dockerfile. The WORKDIR in Docker is a fundamental instruction when working in Dockerfile to set the current working directory within the container.

Prerequisites:

To follow along with the tutorial, you need the following:

Installed Docker on the host machine
Basic knowledge of Docker and Dockerfile syntax

The Basics

Let us start with the basics and discuss what the WORKDIR instruction means.

In a Dockerfile, the WORKDIR directive allows us to set the working directory for any subsequent instructions.

This means that when we run a container from an image built with a Dockerfile containing WORKDIR, the container’s default working directory is set to the specified path.

You can think of the equivalent of the “cd” command in Unix systems.

Using the WORKDIR directive can help prevent the relative-path related errors when running the commands inside the container.

The following shows the syntax for the WORKDIR instruction:

WORKDIR /path/to/directory

Where the “path/to/directive” specifies an absolute or relative path to the directory that you wish to set as the “cwd”.

Basic Usage

Consider the following Dockerfile example that defines the instructions to run a Node.JS application:

FROM node:latest

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

EXPOSE 3000

CMD [ "npm", "start" ]

In the given example, we use the WORKDIR directive to set the current working directory to “/app”. This means that all the subsequent commands run inside the “/app” directory.

Using Relative Paths

Docker also allows us to use the relative paths with the WORKDIR directive. For example, suppose we have a project layout as follows:

app/

├── Dockerfile

├── src/

└── public/

In the Dockerfile, we can set the WORKDIR as a relative path as shown in the following example:

FROM ubuntu

WORKDIR /app

COPY src/ .

In this case, the WORKDIR instruction sets the working directory to “/app” relative to the root directory of the container.

Using Multiple WORKDIR Directives

As you can guess, we can use multiple WORKDIR instructions in the same Dockerfile. This allows us to quickly change the current working directory in single steps.

FROM ubuntu

WORKDIR /app

RUN touch config.ini

# Change the working directory

WORKDIR /data

RUN touch logging.yml

In the given example, we start by defining the current working directory to “/app” using the first WORKDIR entry. We then execute the commands to create a new file inside the “/app” directory.

Next, we change the current working directory to “/data” and create a new file in that directory.

Conclusion

In this tutorial, we learned how to work with the WORKDIR instruction within the Dockerfile to change the current working directory for all subsequent commands.