Reuse local image when already present for pinned tags#339
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gtsiolis merged 2 commits intoJun 25, 2026
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lstk ran docker pull on every start, even when the image was already present locally. On slow networks this meant repeated multi-minute re-downloads for no benefit. Add ImageExists to the Runtime interface (backed by ImageInspect + errdefs.IsNotFound on Docker) and, in pullImages, skip the pull for pinned tags whose image is already local. Emit a "Using local image" message and record pulled[name]=false so start telemetry does not over-count. Floating latest/empty tags still pull until pull_policy support lands. Generated with [Linear](https://linear.app/localstack/issue/PRO-323/reuse-local-image-when-already-present#agent-session-e6210615) Co-authored-by: linear-code[bot] <222613912+linear-code[bot]@users.noreply.github.com>
gtsiolis
added
semver: patch
docs: needed
…olated The previous version started a real LocalStack bound to the shared host port 4566, which collided with the external-container tests after CI's sorted-name shard reshuffle and caused a leaked-container cascade. Tag the lightweight alpine test image under a pinned localstack-pro tag instead: lstk still skips the pull and emits "Using local image" (the decision under test, emitted before the container starts), but the stand-in image exits immediately so start fails fast. A dedicated host port (4599) keeps it off 4566. No real image pull or auth token needed. Generated with [Linear](https://linear.app/localstack/issue/PRO-323/reuse-local-image-when-already-present#agent-session-e6210615) Co-authored-by: linear-code[bot] <222613912+linear-code[bot]@users.noreply.github.com>
anisaoshafi
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Jun 25, 2026
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Good improvement, nice thought. No need to pull images that are already downloaded 💯 Thanks!
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Summary
lstk startrandocker pullon every start, even when the image was already present locally —rt.PullImagewas unconditional. On slow networks this meant repeated multi-minute re-downloads for no benefit.This adds
ImageExiststo theRuntimeinterface (backed byImageInspect+errdefs.IsNotFoundon Docker) and, inpullImages, skips the pull when a pinned-tag image is already local — emitting aUsing local imagemessage instead and recordingpulled[name]=falseso start telemetry (LifecycleStartSuccess.Pulled) doesn't over-count. Stopped-container cleanup (rt.Remove) still runs on both branches, and post-pull license validation is unaffected since the image is present.A net-new probe is needed because
GetImageVersioncan't double as one: it errors both when the image is absent and whenLOCALSTACK_BUILD_VERSIONis missing, conflating the two.Scope
Skip-if-present applies to pinned tags only. Floating
latest/empty still pulls until thepull_policywork lands (PRO-325).Tests
lstk start, assertUsing local imagepresent andPullingabsent.ImageExiststrue → 0PullImagecalls,pulled[name]==false; false → 1 call,pulled[name]==true.