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Vercel Deployment Guidelines

Core Principles

• Always optimize for Vercel's edge network and serverless model
• Prefer Edge Runtime for globally distributed, low-latency responses
• Use Vercel's built-in environment variable management for secrets
• Structure projects to leverage Vercel's zero-config deployment detection
• Always use vercel.json for advanced routing, headers, and redirects configuration

Project Structure

• Place API routes in /api directory for automatic serverless function detection (Pages Router) or /app/api for App Router
• Use public/ for static assets that should be served via Vercel's CDN
• Keep serverless functions small and focused — cold start time matters
• Separate long-running tasks to background jobs or external queues (Vercel has a 10s default timeout on Hobby, 60s on Pro)

Environment Variables

• Never hard-code secrets; always use process.env.VARIABLE_NAME
• Prefix client-side env vars with NEXT_PUBLIC_ (Next.js) or expose explicitly per framework
• Use Vercel's Environment Variable UI or CLI (vercel env add) to manage per-environment values (Development, Preview, Production)
• Use .env.local for local development; never commit it
• Reference vercel.json env field only for build-time non-secret values

vercel.json Configuration

• Use rewrites for proxying API calls or SPA fallback routing
• Use redirects for permanent (308) or temporary (307) URL changes
• Use headers to set security headers (CSP, HSTS, X-Frame-Options) globally
• Use regions to pin serverless functions to specific regions when data locality matters
• Example security headers block:

  {
    "headers": [
      {
        "source": "/(.*)",
        "headers": [
          { "key": "X-Content-Type-Options", "value": "nosniff" },
          { "key": "X-Frame-Options", "value": "DENY" },
          { "key": "X-XSS-Protection", "value": "1; mode=block" },
          { "key": "Referrer-Policy", "value": "strict-origin-when-cross-origin" }
        ]
      }
    ]
  }
  

Serverless Functions

• Keep dependencies minimal — bundle size directly impacts cold starts
• Use Edge Functions (export const runtime = 'edge') for auth checks, redirects, and A/B testing
• Use Node.js runtime for database connections, heavy computation, or Node-only packages
• Always handle errors gracefully and return proper HTTP status codes
• Use streaming responses for LLM or large data outputs

Edge Middleware

• Place middleware in middleware.ts at the project root
• Use middleware for: authentication guards, geo-based redirects, bot protection, and A/B flags
• Keep middleware lightweight — it runs on every request before the cache
• Use matcher config to scope middleware only to needed routes

  export const config = {
    matcher: ['/dashboard/:path*', '/api/:path*'],
  }
  

Performance & Caching

• Use Cache-Control headers to control Vercel's CDN caching behavior
• Use stale-while-revalidate for ISR-like behavior in non-Next.js apps
• Set s-maxage for CDN cache TTL and max-age for browser cache
• Avoid over-fetching in serverless functions — reuse DB connections with connection pooling (PgBouncer, Prisma Accelerate)
• Use vercel/og for dynamic OG image generation at the edge

CI/CD & Preview Deployments

• Use Vercel's GitHub/GitLab/Bitbucket integration for automatic preview deployments per PR
• Use vercel pull + vercel build + vercel deploy --prebuilt in custom CI pipelines
• Set branch protection rules to require passing preview deployment checks
• Use VERCEL_ENV environment variable to differentiate behavior across preview/production

Domain & DNS

• Use Vercel Domains or point external DNS to Vercel's nameservers for automatic SSL
• Always redirect www to apex or vice versa — never serve both
• Use vercel domains add CLI command for custom domain management

Monorepo Support

• Set rootDirectory in project settings to point to the correct app within a monorepo
• Use Turborepo with Vercel Remote Cache for fast CI builds (turbo build --filter=...)
• Scope environment variables per project even in shared monorepos

Databases & Storage

• Prefer Vercel-native storage (Vercel KV, Vercel Postgres, Vercel Blob) for zero-config integration
• For external databases, always use connection pooling — serverless functions do not maintain persistent connections
• Store large files in Vercel Blob or S3-compatible storage, not in the function bundle

Logging & Observability

• Use console.log / console.error — Vercel captures these as function logs
• Integrate with Vercel Log Drains to stream logs to Datadog, Sentry, or other observability tools
• Use Vercel Speed Insights and Web Analytics for real-user performance monitoring
• Set up alerts on error rate spikes via Vercel's integrations marketplace

Security Best Practices

• Enable Vercel's DDoS protection (included on all plans)
• Use Vercel Firewall rules to block malicious IPs and patterns
• Rotate secrets regularly using Vercel's environment variable versioning
• Never log sensitive data (tokens, passwords, PII) in serverless function output
• Use VERCEL_OIDC_TOKEN for secure machine-to-machine auth between Vercel and cloud providers

Deployment Workflow

• Run vercel --prod only from protected branches (main/master)
• Use vercel deploy (without --prod) for staging/preview deployments
• Alias stable preview URLs with vercel alias for QA sign-off
• Use deployment protection (password or Vercel Access) on preview deployments for private projects