Dockerfile.backend

# =============================================================================
# Backend Dockerfile — Python FastAPI Production Image
# =============================================================================
# This Dockerfile creates a container image for the FastAPI backend.
# It follows Docker best practices:
#   1. Use a slim base image to minimize size.
#   2. Copy dependency files first, then install — this leverages Docker's
#      layer caching so dependencies are only reinstalled when they change.
#   3. Copy source code last (it changes most frequently).
#
# Build: docker build -f Dockerfile.backend -t backend .
# Run:   docker run -p 8000:8000 backend
# =============================================================================

# Start from the official Python 3.12 slim image.
# "slim" variants exclude development tools (compilers, man pages, etc.)
# to keep the image small (~150MB vs ~900MB for the full image).
FROM python:3.12-slim

# Copy the `uv` package manager binary from its official Docker image.
# This is a "multi-stage copy" — it grabs just the binary without including
# the rest of the uv image. `uv` is a fast Python package manager that
# replaces pip and manages virtual environments.
COPY --from=ghcr.io/astral-sh/uv:latest /uv /uvx /usr/local/bin/

# Set the working directory inside the container. All subsequent commands
# (COPY, RUN, CMD) will run relative to /app.
WORKDIR /app

# Copy ONLY the dependency files first. Docker caches each instruction as
# a "layer." If these files haven't changed, Docker reuses the cached layer
# and skips the `uv sync` step — saving minutes on rebuilds.
COPY backend/pyproject.toml backend/uv.lock ./

# Install production dependencies (--no-dev excludes test/lint tools).
# --frozen ensures the lock file is used exactly as-is (no resolution).
RUN uv sync --frozen --no-dev

# NOW copy the application source code. This layer changes frequently
# (every code edit), but the dependency layer above is cached.
COPY backend/ .

# Define the default command to run when the container starts.
# - uvicorn: the ASGI server that runs our FastAPI app.
# - app.main:app: import path to the FastAPI instance.
# - --host 0.0.0.0: listen on all network interfaces (required in Docker).
# - --port 8000: the port to serve on.
CMD ["uv", "run", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]