perf: serve images from a static host instead of the API - #397
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nGervasyuk merged 2 commits intoAug 23, 2026
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This was referenced Aug 21, 2026
The API serves images from the same single-threaded process that computes image diffs, so during build ingestion image requests queue behind CPU-bound work and screenshots take seconds to load. The UI container's nginx already exposes the imageUploads volume, so let deployments opt in via REACT_APP_STATIC_URL (e.g. /static/imageUploads) to fetch images from it directly. When unset, images keep going through the API — S3-backed deployments are unaffected.
Socket events arrive for every build, and even an all-filtered-out batch dispatched a state update that replaced the testRuns array — invalidating every memo over it and re-rendering the grid each debounce tick while an unrelated build was ingesting. With thousands of runs open that made the whole UI stutter. Skip empty batches, return the same state when nothing matched, and deduplicate by id via Set/Map instead of nested scans.
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Problem
The UI loads every screenshot through
${API_URL}/images/<name>— the same single-threaded API process that computes image diffs. While a build is ingesting, image requests queue behind CPU-bound comparison work and baseline/checkpoint images take seconds to appear in the test details dialog.Change
New optional
REACT_APP_STATIC_URLruntime env var. When set (e.g./static/imageUploads— the UI container's nginx already mounts the imageUploads volume there), images are fetched directly from the static host and never touch the API. When unset, behaviour is unchanged, so S3-backed deployments keep working through the API redirect.Measured on a local stack during a 4-way concurrent upload burst: image GET through the API — 963 ms median; same file through nginx — 3 ms.
Pairs with Visual-Regression-Tracker/backend#368.
Deploying
REACT_APP_STATIC_URLis opt-in and only applies to HDD-backed deployments, where the UI container already mounts theimageUploadsvolume. Leave it unset on an S3-backed deployment: there the API redirects to storage and images never pass through it anyway, so pointing the UI at a static path that does not exist would break every image. Unset is the default and keeps todays behaviour exactly.The second commit (socket events for other builds no longer re-render the list) helps every deployment regardless of storage.