Optimizing Docker Builds with Build Cache

When building Docker images, it's a good practice to leverage build cache as much as possible. The build cache stores the intermediate layers of an image build, so if you make a change to the Dockerfile, only the layers after the change will be rebuilt, significantly speeding up the build process.

For example to speed up the build process when building docker images for your python applications, one of the ways is through effective utilization of docker's built cache. When changes are made in the Dockerfile, only the layers after that change will be rebuilt because of intermediate layers stored by build cache which spares valuable time.

Dockerfile must be structured in a way that orders instructions from least to most frequently changing in order to benefit from the build cache. The Dockerfile should begin with less dynamic instructions such as installing system dependencies or copying requirement files before ending with more frequently changing instructions such as application code copying.

The following Dockerfile is an example of a Python application using the build cache:

# Use the official Python image as the base
FROM python:3.9

# Set the working directory
WORKDIR /app

# Copy the requirements file
COPY requirements.txt .

# Install Python dependencies
RUN pip install --no-cache-dir -r requirements.txt

# Copy the rest of the application code
COPY . .

# Build static files (if applicable)
RUN python manage.py collectstatic --no-input

# Expose the port the app runs on
EXPOSE 8000

# Start the application
CMD ["python", "manage.py", "runserver", "0.0.0.0:8000"]