dockerfile-best-practices

# Dockerfile Best Practices Reference

## Layer Optimization

### The Golden Rule
Every `RUN`, `COPY`, and `ADD` instruction creates a new layer. Fewer layers = smaller image.

### Combine Related Commands
```dockerfile
# Bad — 3 layers
RUN apt-get update
RUN apt-get install -y curl git
RUN rm -rf /var/lib/apt/lists/*

# Good — 1 layer
RUN apt-get update && \
    apt-get install -y --no-install-recommends curl git && \
    rm -rf /var/lib/apt/lists/*
```

### Order Layers by Change Frequency
```