Docker Multi-Stage Builds for Production

Your Docker images are too big. Let’s fix that.

Before: 1.2GB Image

FROM python:3.11
WORKDIR /app
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . .
CMD ["python", "app.py"]

After: 120MB Image

FROM python:3.11 AS builder
WORKDIR /app
RUN pip install --user --no-cache-dir -r requirements.txt

FROM python:3.11-slim
WORKDIR /app

COPY --from=builder /root/.local /root/.local
COPY app.py .

RUN useradd -m appuser && chown -R appuser:appuser /app
USER appuser

ENV PATH=/root/.local/bin:$PATH
CMD ["python", "app.py"]

Go Example (Even Better)

FROM golang:1.21 AS builder
WORKDIR /app
COPY go.* ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -o server

FROM scratch
COPY --from=builder /app/server /server
ENTRYPOINT ["/server"]

Size Comparison

Approach	Image Size
Python (naive)	1.2GB
Python (multi-stage)	120MB
Go (multi-stage)	15MB
Go (scratch)	8MB

Every megabyte costs money in registry storage and pull time.