Dockerfile

# Stage 1: Build stage using Maven + JDK 21
FROM maven:3.9.6-eclipse-temurin-21-alpine AS builder
WORKDIR /build

# Copy pom.xml first to cache dependencies
COPY pom.xml .
RUN mvn dependency:go-offline -B

# Copy source code and package application
COPY src ./src
RUN mvn clean package -DskipTests -B

# Stage 2: Slim JRE-only runtime stage
FROM eclipse-temurin:21-jre-alpine
WORKDIR /app

# Install curl for container healthcheck
RUN apk add --no-cache curl

# Create non-root system user and group
RUN addgroup -S appgroup && adduser -S appuser -G appgroup

# Copy compiled executable JAR from builder stage
COPY --from=builder /build/target/distributed-file-sharing-*.jar app.jar

# Set file ownership for non-root execution
RUN chown -R appuser:appgroup /app

# Switch to non-root user
USER appuser

EXPOSE 8080

# Healthcheck hitting Spring Boot Actuator endpoint
HEALTHCHECK --interval=10s --timeout=5s --start-period=30s --retries=3 \
  CMD curl -f http://localhost:8080/actuator/health || exit 1

ENTRYPOINT ["java", "-jar", "app.jar"]