perf: serve MDX screenshots as WebP through Next's image optimizer - #2010
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ZoomableImage renders every doc image eagerly, so a long page downloads every screenshot on it before first paint. loading="lazy" defers the ones below the fold until the reader scrolls near them. Amp-Thread-ID: https://ampcode.com/threads/T-01a0b274-3173-77ed-8f71-82301b157a16 Co-authored-by: Amp <amp@ampcode.com>
Amp-Thread-ID: https://ampcode.com/threads/T-01a0b274-3173-77ed-8f71-82301b157a16 Co-authored-by: Amp <amp@ampcode.com>
The docs embed ~360 PNG screenshots from GCS (sourcegraphstatic.com and storage.googleapis.com/sourcegraph-assets), uncompressed and with a one-hour cache. Route allow-listed PNG/JPEG sources through /_next/image, which converts to WebP, caps width at 1920px and caches at Vercel's edge for a week. The zoom modal keeps the original full-resolution file. Amp-Thread-ID: https://ampcode.com/threads/T-01a0ac9d-704f-73fe-8211-1b3e5840969f Co-authored-by: Amp <amp@ampcode.com>
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Stacked on #1975. Diff against that branch is the only thing to review here.
Problem
MDX screenshots are uncompressed PNGs on GCS (
sourcegraphstatic.com,storage.googleapis.com/sourcegraph-assets), served withmax-age=3600and no format negotiation./batch-changes/delete-a-batch-changeships 1.2 MB of PNG for four images.Those images sit behind no CDN today. Response headers show the request path is Cloudflare → Google front end → Vercel edge for HTML and static assets, but
sourcegraphstatic.comis a separate zone on Google Cloud DNS pointing straight at a GCS load balancer: no Cloudflare, no Cloud CDN, no Vercel. Vercel's image optimizer has never been used on this project (zero transformations in the billing export for August and September).Fix
ZoomableImagepoints allow-listed remote PNG/JPEGs at/_next/image: WebP, capped at 1920 px wide, cached at Vercel's edge for a week (minimumCacheTTL). The allow-list lives indocs.config.jssonext.config.js(images.remotePatterns) andZoomableImageshare it. SVG, GIF and other hosts pass through unchanged. The zoom modal keeps the original full-resolution file.Measured with
next start, the four images on the page above:/_next/imageCost
From the Vercel billing API (
/v1/billing/charges) for theSourcegraphteam, which is on Pro:docs-legacy-versions), $0.docs/, one variant each (w=1920&q=75, WebP), refreshed weekly ≈ 1–2K transformations and ~10–20K cache-write units a month. Pro's included allotment covers that; past it, transformations are $0.05 per 1K.sourcegraph-docsruns 40–60 GB/month. Even at 500K image-page views a month (~100 GB) this stays inside the included capacity, at $0.Trade-offs
minimumCacheTTLto fall back to Next's 4 h default if that matters.w=1920is the largest of Next's defaultdeviceSizesthat still covers the content column on a 2x display; wider screenshots are downscaled. The zoom modal still loads the original.sourcegraphstatic.combehind Cloudflare would be a further improvement (free egress, closer edge) but is an infra change to a shared bucket's DNS, tracked separately.Verification
tsc,eslint,cspellclean. Onnext start(earlier revision of this branch): everysourcegraphstatic.comPNG on the page renders through/_next/imageasimage/webpwithCache-Control: public, max-age=604800; a PNG from a bucket outside the allow-list returns 400. Page renders unchanged. Will re-check on the Vercel preview once it deploys.