Improve Dockerfile layer caching#239
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Previously: ADD S6 → RUN (apk upgrade + S6 extract + apk add) → pip A S6 bump invalidated the apk and pip layers every time. Now: RUN apk → ADD S6 → RUN S6 extract → pip Each concern is an independent cacheable layer. A S6 bump only invalidates S6 extract onward; an apk-only change doesn't touch S6 or pip; a requirements.txt change only rebuilds pip. Also adds --mount=type=cache for apk to mirror the existing pip cache mount, and removes --no-cache from apk add so the BuildKit cache mount is actually used. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
DL3005/DL3019: apk upgrade and no --no-cache (intentional — using BuildKit cache mount instead of --no-cache for better layer reuse) DL3059: consecutive RUN instructions (intentional split for cache granularity) Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
DL3006 on the dynamic FROM base-${TARGETARCH} line — version is
controlled via ARG, not a literal tag.
DL3018 on apk add — already overridden to style in .hadolint.yaml
but inline ignore needed to suppress diff annotations.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
Reorders Dockerfile layers so each concern caches independently. Previously a S6 version bump invalidated the entire
apk add(55 packages) andpip installchain.Before:
After:
Cache impact per change type:
requirements.txtchangeAlso adds
--mount=type=cache,id=apk-${TARGETARCH}to the apk step (mirrors the existing pip cache mount), and inline# hadolint ignoredirectives for rules that are intentionally violated by this approach (DL3005,DL3006,DL3018,DL3019,DL3059).Test plan