Q: Your microservice image size has crept up to 850MB despite the compiled application binary being only 30MB. Developers attempted cleaning up build tools by running `apt-get clean` in subsequent `RUN` commands, unaware that files created in earlier image layers remain permanently baked into the image history. Image push and pull times are degrading pipeline performance. You need to use `dive` to inspect layer deltas, identify wasted space, and enforce an image efficiency gate in GitHub Actions.

In Docker's union filesystem (OverlayFS), each `RUN`, `COPY`, and `ADD` instruction creates a new read-only layer. Deleting or modifying a file in a later layer (`RUN rm -rf /tmp/build`) does not reclaim space; it merely creates a whiteout marker masking the file while preserving the underlying bytes in previous layers.

<!-- Layer Immutability Pitfall -->
Layer 1: RUN apt-get update && apt-get install -y build-essential  (+300MB)
Layer 2: RUN ./compile-app.sh                                      (+30MB)
Layer 3: RUN apt-get purge -y build-essential && rm -rf /var/lib/apt (+10KB whiteout)

Result: Image size is still 330MB! Build-essential bytes still exist in Layer 1!

Run `dive ` to inspect the layer-by-layer diff. Dive highlights wasted space, file modifications between layers, and assigns an efficiency score percentage.

# Run interactive inspection with dive
dive my-bloated-app:latest

# Key UI metrics in dive:
# - Efficiency Score (e.g., 68%)
# - Wasted Bytes (e.g., 280MB duplicated or deleted across layers)
# - Layer view: toggle between added, modified, and removed files

Combine package installation, compilation, and cache cleanup into a single contiguous `RUN` instruction so temporary build assets are purged before the layer is committed.

# Efficient single-layer pattern
RUN apt-get update && apt-get install -y --no-install-recommends \
    curl \
    ca-certificates \
    && rm -rf /var/lib/apt/lists/* \
    && rm -rf /tmp/* /var/tmp/*

Integrate `dive` into automated CI pipelines with non-interactive flags (`CI=true`). Fail the build if the image efficiency drops below 95% or if wasted space exceeds 20MB.

# CI Pipeline Step
- name: Check Image Efficiency with Dive
  env:
    CI: true
  run: |
    curl -sL https://github.com/wagoodman/dive/releases/download/v0.12.0/dive_0.12.0_linux_amd64.tar.gz | tar -xz
    ./dive my-app:latest --ci --lowestEfficiency=0.95 --highestWastedBytes=20MB