Dockerfile

# Multi-stage build for C++20 DNS server

# Build stage
FROM ubuntu:24.04 AS builder

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

WORKDIR /build

# Copy source files
COPY CMakeLists.txt .
COPY include/ include/
COPY src/ src/
COPY tests/ tests/

# Build release binary
RUN cmake -B build -DCMAKE_BUILD_TYPE=Release -DBUILD_TESTS=OFF \
    && cmake --build build --parallel

# Runtime stage
FROM ubuntu:24.04 AS runtime

RUN apt-get update && apt-get install -y \
    libstdc++6 \
    && rm -rf /var/lib/apt/lists/*

# Create non-root user
RUN useradd -r -s /bin/false dnsserver

WORKDIR /app

# Copy binary from builder
COPY --from=builder /build/build/dns_server /app/dns_server

# Copy entrypoint script
COPY docker-entrypoint.sh /app/docker-entrypoint.sh
RUN chmod +x /app/docker-entrypoint.sh

# DNS uses UDP port 53
EXPOSE 53/udp

# Run as root for port 53 binding (required for privileged ports)
# Use --cap-add=NET_BIND_SERVICE in production for non-root binding
USER root

ENTRYPOINT ["/app/docker-entrypoint.sh"]