Field Notes: What Actually Happens When You Deploy 7 Next.js Subdomains to Vercel

After deploying seven Next.js subdomains to Vercel for a single brand network, here is what we learned that no tutorial covers.

The deployment itself is straightforward: each subdomain is its own Vercel project with its own `vercel.json` and custom domain alias. The Vercel CLI command `vercel --prod --yes` handles it in under 40 seconds per project. But the real complexity is in DNS propagation and SSL certificate provisioning.

What surprised us: Vercel provisions SSL certificates asynchronously after you add a custom domain. We added `blog.j3cfamily.studio` and `admin.j3cfamily.studio` to our main project, and the certificates were still being issued hours later. The domains resolved to Vercel's IPs immediately, but HTTPS took longer.

The subdomain architecture we used: tools, calculators, privacy, seo, ai, templates, and quiz — each as a separate Next.js 14 or 16 project. Four used static export (`output: 'export'`), while three (ai, templates, quiz) used server-side rendering. The static exports built in under 10 seconds; the SSR projects took 30-45 seconds.

Cross-linking between subdomains is critical for SEO but inconsistent in practice. Our newer subdomains (ai, quiz) link to all 9 properties in the network, while older ones (tools, calculators) only link to 4. Updating footers across 7 projects is tedious but necessary for topical authority.

The deploy-all script we wrote iterates through each subdomain, runs `npm install`, `npm run build`, and `vercel --prod`, then attaches the custom domain. Total time for all 7: about 6 minutes.

Practical takeaway: Deploy subdomains as separate Vercel projects for isolation and independent scaling. Budget extra time for DNS and SSL propagation. Write a batch deploy script early — it saves hours over manual deployments.