Dockerfile.three-stage

# ============================================================================
# THREE-STAGE DOCKERFILE (ADVANCED OPTIMIZATION)
# ============================================================================
# Architecture based on change frequency and package sources:
#
# BASE:    CRAN packages (stable, rarely change) + build tools
# BUILDER: Custom/private packages (change independently from CRAN)
# RUNTIME: Pure application + runtime libraries only (NO build tools)
#
# Key advantages:
# 1. CRAN packages cached separately from custom packages
# 2. Custom package changes don't invalidate CRAN package layer
# 3. Runtime image is completely clean - no build tools whatsoever
# 4. Optimal layer caching based on change frequency
# ============================================================================

# ============================================================================
# STAGE 1: Base - CRAN packages and build environment
# ============================================================================
FROM rocker/r2u:24.04 AS base

# Configure renv cache to use the same path as runtime
# This ensures symlinks remain valid when copied to runtime stage
ENV RENV_PATHS_CACHE="/app/renv/.cache"

# Install system dependencies needed for compilation AND runtime
# Build tools are needed here to compile CRAN packages
RUN apt-get update && apt-get install -y \
    # Build tools (needed for CRAN package compilation)
    libcurl4-openssl-dev \
    libssl-dev \
    libxml2-dev \
    libfontconfig1-dev \
    libharfbuzz-dev \
    libfribidi-dev \
    libfreetype6-dev \
    libpng-dev \
    libtiff5-dev \
    libjpeg-dev \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /app

# OPTIMIZATION 1: Copy only dependency files first
# This creates a cache-friendly layer that only rebuilds when CRAN dependencies change
COPY renv.lock renv.lock
COPY .Rprofile .Rprofile
COPY renv/activate.R renv/activate.R
COPY renv/settings.json renv/settings.json

# OPTIMIZATION 2: Install renv and restore CRAN packages
# This layer is cached unless renv.lock changes
# CRAN packages change rarely, so this provides excellent caching
RUN R -e "install.packages('renv', repos = 'https://cloud.r-project.org')"
RUN R -e "renv::restore()"

# ============================================================================
# STAGE 2: Builder - Custom/private packages
# ============================================================================
FROM base AS builder

# Inherit all CRAN packages and build tools from base
# Add any additional build dependencies for custom packages here if needed
# RUN apt-get update && apt-get install -y \
#     <additional-build-deps> \
#     && rm -rf /var/lib/apt/lists/*

WORKDIR /build

# Copy and build custom packages (not on CRAN)
# These might be:
# - Private packages from GitHub/GitLab
# - Internal company packages
# - Packages built from local source
#
# Example (uncomment and modify as needed):
# COPY custom_packages/ custom_packages/
# RUN R CMD INSTALL custom_packages/mypackage

# For now, just inherit from base
# In a real scenario, you'd install custom packages here:
# RUN R -e "remotes::install_github('yourorg/yourpackage')"

# Copy application code
# This is the most frequently changing layer
COPY app.R app.R

# ============================================================================
# STAGE 3: Runtime - Pure application (NO build tools)
# ============================================================================
FROM rocker/r2u:24.04

# Configure renv cache location to match where packages were installed
ENV RENV_PATHS_CACHE="/app/renv/.cache"

# Install ONLY runtime system dependencies (no -dev packages, no build tools)
# Note: Using minimal runtime libraries without -dev packages
RUN apt-get update && apt-get install -y --no-install-recommends \
    libcurl4 \
    libssl3 \
    libxml2 \
    libfontconfig1 \
    libharfbuzz0b \
    libfribidi0 \
    libfreetype6 \
    libpng16-16t64 \
    libtiff6 \
    libjpeg-turbo8 \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /app

# Copy CRAN packages from base stage (includes cache at /app/renv/.cache)
COPY --from=base /app/renv /app/renv
COPY --from=base /app/.Rprofile /app/.Rprofile
COPY --from=base /app/renv.lock /app/renv.lock

# Copy custom packages from builder stage (if any were installed)
# COPY --from=builder /usr/local/lib/R/site-library/mypackage /usr/local/lib/R/site-library/mypackage

# Copy application code from builder
COPY --from=builder /build/app.R /app/app.R

# Expose Shiny port
EXPOSE 3838

# Run the application
# Note: Use --vanilla to skip .Rprofile and avoid renv activation at runtime
# The renv library path is already in R's search path
CMD ["R", "--vanilla", "-e", ".libPaths('/app/renv/library/linux-ubuntu-noble/R-4.5/x86_64-pc-linux-gnu'); shiny::runApp('/app', host = '0.0.0.0', port = 3838)"]

# ============================================================================
# Layer Optimization Strategy:
# ============================================================================
#
# CRAN packages (base):        Changes LEAST frequently   → Cached most aggressively
# Custom packages (builder):   Changes MORE frequently     → Independent cache layer
# Application code (runtime):  Changes MOST frequently     → Doesn't invalidate above
#
# Build flow:
# 1. Base layer compiles CRAN packages (cached unless renv.lock changes)
# 2. Builder adds custom packages (cached unless custom package sources change)
# 3. Runtime copies everything and adds application code
# 4. Code changes only invalidate the final COPY app.R step
#
# ============================================================================
# Build and Run Commands:
# ============================================================================
# Build (three-stage):
#   docker build -f Dockerfile.three-stage -t shiny-app:three-stage .
#
# Run:
#   docker run -p 3838:3838 shiny-app:three-stage
#
# Verify no build tools in runtime:
#   docker run --rm shiny-app:three-stage dpkg -l | grep -E "dev|gcc|g\+\+"
#   (should return nothing)
#
# Compare sizes:
#   docker images | grep shiny-app
# ============================================================================