Serverless Audit PDF Generation with Puppeteer and Chromium on Vercel

Avo's sales motion required generating proposal and audit PDFs on demand. A prospect books a discovery call, the system pulls their company data, and within seconds a polished PDF brief lands in their inbox. The PDF needed to include dynamic content, consistent typography, and controlled layout. It also needed to generate in a serverless environment where installing native binaries is not an option.

Hosted PDF generation services were ruled out by the build-don't-rent mandate. Consumption of a managed API at per-document pricing compounds into a meaningful cost at 1,000 documents per month and creates a hard external dependency in the sales pipeline. React-PDF was evaluated but its subset of CSS support did not handle the layout without extensive rework of the design system. Puppeteer with @sparticuz/chromium was the correct choice: it runs a real Chromium instance in a serverless function, renders an HTML/CSS document, and exports it via page.pdf(). The challenge was that a full Chromium binary exceeds Vercel's function size limit of 50 MB. The @sparticuz/chromium package is a Lambda/Vercel-compatible Chromium build compressed with Brotli, under 50 MB.

The HTML templates were standard Next.js server-rendered pages served from internal routes under /api/pdf-templates/[type]. The Puppeteer function navigated to the internal template URL with query parameters encoding the document content. The template route returned an HTML page with all styles inlined and no external font requests, because fonts were base64-encoded as data URIs in the CSS. No JavaScript execution was required on the rendered page.

The PDF generation function ran on a Vercel Serverless Function with a 60-second timeout. The p99 generation time for a 4-page proposal PDF was 8.2 seconds, well within the timeout. The 60-second ceiling existed to handle cold-start decompression of Chromium, which added 3 to 5 seconds on the first invocation.

The core function sequence: validate request and authenticate with Clerk; fetch company data from ClickHouse; construct the template URL; launch Chromium via chromium.executablePath(); open a Puppeteer Browser instance; navigate to the template URL; generate PDF; close the browser; upload PDF buffer to Vercel Blob storage; return signed Blob URL with 7-day expiry; trigger Resend email with the Blob URL.

A significant constraint was that the internal template URL required resolution. In serverless deployments, localhost:3000 is not a reliable address because the function runs isolated from the Next.js server. The fix was to construct the template URL using the Vercel deployment URL from the VERCEL_URL environment variable.

Memory configuration: the default Vercel Serverless Function memory allocation of 1,024 MB was insufficient for Chromium at peak. Functions exceeded memory on documents with large signal tables. The function was reconfigured to 3,008 MB. Peak resident set size during PDF generation was 1,840 MB.

Font handling: the first version fetched Geist fonts from Google Fonts CDN at render time. Puppeteer observed the networkidle wait condition as satisfied before fonts had loaded, because font requests fired asynchronously after CSS parse. The result was fallback system font in 40 to 60% of PDFs. The fix inlined all fonts as base64 data URIs in a style block inside the template.

214 documents were generated across proposal and audit categories in the first 30 days. Total infrastructure cost for PDF generation was under $1 per month in Vercel invocation compute plus Vercel Blob storage at negligible scale. This compared favorably to managed PDF services, which would have priced at $0.10 to $0.25 per document.