The cache
Three things that do not invalidate the cache
Received wisdom about the build cache is unusually wrong. These three are recorded against a real builder, not remembered.
Why these are recorded rather than asserted
The cache rule is simple enough to state in three lines and is surrounded by folklore that is confidently wrong. This gym records every claim it makes against a real Docker builder running in a pinned container before the claim is written down.
Three of the things on this page were written into this engine from ordinary received wisdom, contradicted by a recording, and corrected. They are here because each of them still sounds right.
Dockerfile
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Layers
Nothing has been built yet. Press Build and the layers, the digest and the cache ledger appear — not before.