Cache-Efficient Dockerfile Guidelines with docker buildx (or buildKit)

Under the hood, we use buildkit (opens in a new tab) (or docker buildx (opens in a new tab)) to build docker images. This allows us to take advantage of advanced caching mechanisms to improve build times and reduce resource consumption. In this guide, we'll provide some guidelines for creating cache-efficient Dockerfiles.

Introduction

Building a cache-efficient Dockerfile is crucial for improving the build time and reducing resource consumption. Docker Buildx and BuildKit provide advanced features that enhance caching mechanisms. This document provides guidelines for creating such Dockerfiles.

Check out the Docker buildx documentation (opens in a new tab) for more information.

General Guidelines

1. Minimize Layers

Each RUN, COPY, or ADD instruction creates a new layer. Minimize the number of layers by combining commands.

Bad Example:

RUN apt-get update
RUN apt-get install -y curl

Good Example:

RUN apt-get update && apt-get install -y curl

2. Leverage Layer Caching

Order instructions from least to most frequently changing to maximize layer caching.

Example:

# Install dependencies (changes less frequently)
COPY requirements.txt /app/
RUN pip install -r requirements.txt
 
# Copy application code (changes more frequently)
COPY . /app

3. Use --mount=type=cache

Utilize BuildKit's --mount=type=cache to cache directories across builds.

Example:

# syntax=docker/dockerfile:1.3-labs
FROM python:3.9
 
# Use BuildKit cache for pip
RUN --mount=type=cache,target=/root/.cache/pip \
    pip install --upgrade pip
 
COPY requirements.txt /app/
RUN --mount=type=cache,target=/root/.cache/pip \
    pip install -r requirements.txt
 
COPY . /app

4. Multi-Stage Builds

Use multi-stage builds to reduce the final image size by copying only the necessary artifacts from intermediate stages.

Example:

# syntax=docker/dockerfile:1.3
FROM python:3.9 AS builder
WORKDIR /app
COPY . .
RUN pip install --upgrade pip \
 && pip install -r requirements.txt
 
FROM python:3.9-slim
COPY --from=builder /app /app
WORKDIR /app
ENTRYPOINT ["python", "app.py"]

5. Clean Up After Installations

Remove unnecessary files and caches after installing packages to keep the image size small.

Example:

RUN apt-get update && apt-get install -y \
    build-essential \
 && rm -rf /var/lib/apt/lists/*

6. Use .dockerignore

Specify files and directories to ignore during the build process to avoid unnecessary files in the build context.

Example:

__pycache__
*.pyc
*.pyo

Example Dockerfile

Here is an example of a cache-efficient Dockerfile using the principles outlined above:

# syntax=docker/dockerfile:1.3
FROM python:3.9 AS base
WORKDIR /app
 
# Install dependencies
COPY requirements.txt ./
RUN --mount=type=cache,target=/root/.cache/pip \
    pip install --upgrade pip \
 && pip install -r requirements.txt
 
# Copy source files
COPY . .
 
# Build the application
RUN python setup.py build
 
# Production image
FROM python:3.9-slim
COPY --from=base /app /app
WORKDIR /app
ENTRYPOINT ["python", "app.py"]

fal Platform Specific Gotchas

When deploying your application on the fal platform, you don't need to worry about enabling Docker Buildx or BuildKit. We take care of it for you. However, you can follow the guidelines mentioned above to create efficient Dockerfiles that will help speed up the build process and reduce resource consumption.

1. Interacting with the local filesystem

COPY and ADD (from local filesystem) are not supported as of now to copy files into the container from the host. Instead you can use fal's fal.toolkit to upload files and refer them in the container using links.

json_url = File.from_path("my-file.json", repository="cdn").url
 
dockerfile_str = f"""
FROM python:3.11-slim
RUN apt-get update && apt-get install -y curl
RUN curl '{json_url}' > my-file.json
"""

or you can use ADD to directly download the file from the URL:

json_url = File.from_path("requirements.txt", repository="cdn").url
 
dockerfile_str = f"""
FROM python:3.11-slim
ADD {json_url} /app/requirements.txt
WORKDIR /app
RUN pip install -r requirements.txt
"""

Conclusion

By following these guidelines, you can create Dockerfiles that build efficiently and take full advantage of Docker Buildx and BuildKit's caching capabilities. This will lead to faster build times and reduced resource usage.

For more detailed information, refer to the Docker documentation (opens in a new tab).