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Docker containers have become the de facto way to manage software and dependencies in different environments. When working with real-world applications, you will undoubtedly need to create a Dockerfile before you can build your application container image.

Use Dockerfile to create a directory in the container using the mkdir command

In addition to allowing developers to assemble only the commands needed to create a Docker image, we can do more with Dockerfiles. To successfully create a Docker image using a Dockerfile, you must understand some basic commands.

Some of the most commonly used commands include:

• FROM - creates the parent/base image layer to be used.
• WORKDIR - allows us to set the working directory.
• COPY - allows us to copy the contents of the current directory to a directory in the container.
• PULL - Add files from your Docker repository.
• RUN - command to be executed when we want to build the image.
• CMD - Specifies the command to run when the container starts.
• ENV - Defines environment variables used during the build.
• ENTRYPOINT - Specifies the command to run when the container starts.
• MAINTAINER - specifies the author of the image.

Using the above command, we can create a Dockerfile as shown below, which uses Python as the base image.

Code:

#  base image
FROM Python

# Set your working directory
WORKDIR /var/www/
# Copy the necessary files
COPY ./app.py /var/www/app.py
COPY ./requirements.txt /var/www/requirements.txt

# Install the necessary packages
RUN pip install -r /var/www/requirements.txt
# Run the app
CMD ["echo", "Hello, Developer"]

This Dockerfile is part of a simple Flask application that just prints a message to the console. If you are interested in creating the same application, here is the requirements.txt file.

click==8.0.4
Flask==2.0.3
gunicorn==20.1.0
itsdangerous==2.1.0
Jinja2==3.0.3
MarkupSafe==2.1.0
Werkzeug==2.0.3

The main file app.py which contains the main application file is shown below.

Code:

from flask import Flask

app = Flask(__name__)

def hello():

    print("Hello, this is a simple Flask application")

hello()

Now, to create a directory in our Docker container's file system using the mkdir command, we will use the RUN command as shown below.

#  base image
FROM Python

# Set your working directory
WORKDIR /var/www/
# Copy the necessary files
COPY ./app.py /var/www/app.py
COPY ./requirements.txt /var/www/requirements.txt

# Install the necessary packages
RUN pip install -r /var/www/requirements.txt
RUN mkdir -p /var/www/new_directory
# Run the app
CMD ["echo", "Hello, Developer"]

The command RUN mkdir -p /var/www/new_directoryallows you to create a directory in your Docker file system called new_directory, which we will eventually build using the image built using the above Docker file.

However, we will first build a Python based Docker image as a base image by running the following command.

isaac@DESKTOP-HV44HT6:~/my-app$ docker build -t new_image .

Output:

docker imagesConfirm that we have successfully built the Docker image from the Docker file using the following command.

$ docker images

Output:

REPOSITORY   TAG       IMAGE ID       CREATED          SIZE
new_image    latest    7ab964c50876   13 minutes ago   932MB

Now that we have a Docker image, we can go ahead and create a Docker container and confirm that a directory called new_directory is created. As shown below, we need to start Bash inside the container to navigate the directory inside the Docker container.

$ docker run -it new_image bash
root@ea42f35d5404:/var/www#

You'll notice that new_directory is created after listing the files in that directory. Apart from that, we can also navigate the directory itself and even create new files in it.

root@ea42f35d5404:/var/www# ls
app.py  new_directory  requirements.txt
root@ea42f35d5404:/var/www# cd new_directory
root@ea42f35d5404:/var/www/new_directory# ls
root@ea42f35d5404:/var/www/new_directory# touch new_file
root@ea42f35d5404:/var/www/new_directory# ls
new_file