backend/Dockerfile

```dockerfile
FROM node:18-alpine

WORKDIR /app

# Copy package files
COPY package*.json ./

# Install dependencies
RUN npm install --only=production

# Copy source code
COPY . .

# Create non-root user
RUN addgroup -g 1001 -S nodejs
RUN adduser -S deepsite -u 1001

# Change ownership of the app directory
RUN chown -R deepsite:nodejs /app
USER deepsite

EXPOSE 5000

# Health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
  CMD node -e "require('http').get('http://localhost:5000/api/health', (res) => { process.exit(res.statusCode === 200 ? 0 : 1) })"

CMD ["npm", "start"]
```