Multi-Stage

Multi-stage builds in Docker help create smaller, more efficient images by separating the build environment from the final production image.

Important info Multi-stage Dockerfile does not create n images i.e., if you have 3 stages it will only build final image. Moreover, you can also specify the only stage to build. Below are some important information you might like to know for building an image

• .dockerignore: A file used to specify files and directories that should be excluded from the Docker build context.

• requirements.txt: Lists the Python packages required for a project, usually used with pip to install dependencies.

• pip wheel: A command to build wheels for Python packages, which are a built package format for faster installation.

• --no-install-recommends build-essential: An option in package management to install only the essential components required, skipping optional packages.

• --no-cache-dir: An option for pip to disable caching of packages, ensuring freshly downloaded packages each time.

• --wheel-dir: Specifies the directory where built wheel files should be stored.

• --no-index: Tells pip not to use the package index, often used with a local wheel repository.

• --find-links: Instructs pip to search for package archives in the specified URL or directory before consulting the Python Package Index.

The following examples were generated by OpenAI and then verified by Edugated, as not everything generated by AI is accurate. Yes, there were errors when the code from OpenAI was executed, and the corrected version is provided below.

// Dockerfile without Multi-stage
FROM python:3.9-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
EXPOSE 8000
CMD ["python","app.py"]

// Dockerfile with Multi-Stage
# Builder stage
FROM python:3.9-slim as builder

WORKDIR /app

# Install build dependencies
RUN apt-get update && \
    apt-get install -y --no-install-recommends build-essential

# Copy requirements file
COPY requirements.txt .

# Install wheel package & Compile dependencies into wheel files
RUN pip install --no-cache-dir wheel && pip wheel --no-cache-dir --wheel-dir /app/wheels -r requirements.txt


# Production stage
FROM python:3.9-slim

WORKDIR /app

# Install pip
RUN pip install --no-cache-dir pip

# Copy wheel files from builder stage
COPY --from=builder /app/wheels /wheels

COPY requirements.txt .

# Install dependencies from wheel files
RUN pip install --no-cache-dir --no-index --find-links=/wheels -r requirements.txt

# Copy application source code
COPY . .

EXPOSE 8080

CMD ["python", "app.py"]

Understanding the Difference Between Single-Stage and Multi-Stage Dockerfiles

What’s the difference? Actually... nothing—at least at first glance! Wait, how can that be? Let’s break it down.

Imagine a Dockerfile without multi-stage builds. In our case, it only includes a requirements.txt file for dependencies. This setup is straightforward and works well for simple use cases.

BUT—and this is a big "but"—this simplicity assumes an ideal scenario. In real-world development, the story is quite different.

The Reality of Development Environments

A typical development container or virtual machine running your web application would likely include:

• Toolchains (compilers, debuggers, etc.)

• Bytecode files (intermediate artifacts)

• Testing frameworks like pytest for automated tests

These extra tools are great for development but add unnecessary bulk when you deploy your application. Imagine shipping all these extras to production—this would increase image size, slow down deployments, and could even introduce security vulnerabilities.

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Why Multi-Stage Builds Shine in Production

In production, you only need the essentials:

• Dependencies required for the application to run

• The application code itself

This is where multi-stage builds save the day. Multi-stage builds let you:

1. Use one stage to install and compile all the extras you need during development (like compilers and testing frameworks).

2. Use a second, "slim" stage to copy only the necessary files into the final image, leaving behind all the development-related baggage.

By adopting multi-stage builds, you create lightweight and secure Docker images that are tailor-made for production environments. It's a simple yet powerful approach that transforms how applications are built and shipped!

A simple example is great for practice, but it won’t fully showcase how multi-stage builds shine in real-world scenarios. To truly grasp their benefits, I recommend exploring this Medium article for an in-depth explanation of how multi-stage builds are applied in production. For a broader understanding, be sure to check out the official Docker documentation.