Learn how this documentation provider uses Vercel and Next.js to achieve efficient multi-tenancy, faster development cycles, and 50-80% faster load times.
Fern is improving how teams build and host documentation. As a multi-tenant platform, Fern enables companies like Webflow and ElevenLabs to create, customize, and serve API documentation from a single Next.js application—scaling seamlessly across multiple customer domains. With 6 million+ page views per month and 1 million+ unique visitors, performance and reliability are key.
By running on Vercel’s infrastructure, Fern benefits from automatic caching, optimized content delivery, and instant scalability, all while maintaining a fast iteration cycle for development. Additionally, their migration to Next.js App Router has driven a 50-80% reduction in page load times, improving navigation speed and Lighthouse scores for customers worldwide.
Link to headingBuilding a multi-tenant platform on Vercel
Fern’s architecture is built around a single Next.js app running on Vercel, handling multi-tenant routing across various customer domains. Instead of deploying separate instances for each customer, Fern uses Vercel Middleware to dynamically route traffic, keeping infrastructure simple and efficient.
The team’s deployment strategy includes a main multi-tenant stack at prod.ferndocs.com, a performance-optimized version at app.ferndocs.com focused on CDN delivery, and a dedicated development environment at dev.ferndocs.com. With Vercel's custom domain support, they also give customers full control over their documentation URLs.
With Vercel's domain management tools, Fern supports both subdomains (docs.website.com) and subpaths (website.com/docs), enabling customers to bring their own domains with just a CNAME DNS record.
How to build a multi-tenant app with custom domains using Next.js
Create a full-stack application with multi-tenancy and custom domain support using Next.js App Router, Vercel Postgres, and the Vercel Domains API.
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Link to headingOptimized deployments for rapid iteration
Fern used to rely on AWS Fargate to run backend services, including a critical indexing script that handled reads and writes to their database and populated Algolia. But deployment through AWS CDK came with a 30-minute feedback loop, from merge to live deploy, which made iteration painfully slow.
By incrementally shifting this work to Vercel Functions, Fern cut deploy times down to five minutes and gained the ability to test changes in preview environments before shipping to production.
Overall Vercel deployments have helped them:
Deploy multiple times per day to enabe tight feedback loops and continuous iteration
Manual Promote allows the team to confidently push updates to production
Instant Rollbacks help avoid the impact of bugs or regressions
By leveraging Vercel’s monorepo support for their open-source repo, Fern deploys updates across all customer sites in minutes, without managing infrastructure overhead.
Link to headingEnterprise-grade performance
For businesses, fast-loading documentation is critical. Fern’s customers choose its platform not just for the UI, but for the speed and performance advantages it inherits from Vercel’s CDN.
Vercel delivers content globally to reduce latency, while automatic caching and Incremental Static Regeneration (ISR) ensure that documentation stays current without triggering full site rebuilds. Native video hosting adds another layer of polish to the developer experience, particularly for onboarding, by eliminating the need for third-party platforms and enabling faster, integrated playback.
Link to headingOne more thing, Next.js App Router
Recently, Fern successfully migrated 65% of its platform from Pages Router to App Router in just 7 days, unlocking major performance gains:
50-80% faster load times for documentation pages
3x faster time to first byte (1.63s → 0.55s at p95)
React Suspense & loading.tsx for smoother navigation
To validate these improvements, Fern stress-tested their API documentation platform with with 6,000 simultaneous GET requests, ensuring fast, stable response times across all customer sites.
Link to headingA platform built for growth
With 63% month-over-month growth, Fern is rapidly scaling to serve customers worldwide. Their ability to iterate quickly, handle customer-specific configurations, and optimize for performance has made them the go-to documentation platform for enterprise companies who demand speed, customization, and availability.
Every single day customers ask for more features. Vercel lets us focus on shipping user-facing functionality, abstracting away the infrastructure that would otherwise slow us down.Danny Sheridan Co-founder and CEO
By leveraging Vercel’s infrastructure, Next.js App Router, and edge caching, Fern delivers a high-performance, multi-tenant documentation experience without the complexity of managing traditional infrastructure.
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