Layer CachingAdvanced
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dockerfileHow does Docker Layer Caching work and how do you optimize it?
Explanation & Concept
Each Dockerfile instruction creates a cached layer. If a layer's inputs haven't changed, Docker reuses the cached layer and skips rebuilding.
However, **if a single layer is invalidated, all subsequent layers must be rebuilt from scratch**.
Code Example
dockerfile
# GOOD: Infrequently changing layers first
FROM python:3.11-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install -r requirements.txt # Cached unless requirements.txt changes!
COPY . . # Changes frequently; placed lastHow It Works & Key Takeaways
Placing frequently changing application code at the very end ensures dependency downloads are cached across builds.
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