Gatsby to Next.js Migration: Technical Reference Guide

Critical Context & Failure Scenarios

Production Breaking Points

• Memory crashes at 7.2GB during createPages - Common with 4,000+ pages
• Build failures at page 2,847-3,156 - JavaScript heap exhaustion, exit code 137
• iOS Safari JavaScript failures - Polyfills not loading properly in production
• URL structure changes cause 80% 404 rate - Trailing slash differences break SEO
• Image double lazy-loading - gatsby-image conflicts with next/image causing no loads

Migration Tax (Unavoidable Conversion Work)

• Converting GraphQL queries to fetch calls: 2-3 hours per complex query
• Replacing Gatsby plugins: 2-4 hours per plugin
• Image optimization migration: 6-8 hours for media-heavy sites
• Routing and slug handling: 4-6 hours for complex URL structures
• SEO and metadata reimplementation: 3-4 hours

Technical Specifications

Performance Improvements

Metric	Gatsby (Before)	Next.js (After)	Impact
Build time	47 minutes	4 minutes	90% faster
Memory usage	7.2GB peak	1.8GB peak	75% reduction
Build success rate	53%	97%	Eliminates deployment failures
Developer debugging time	20 hours/month	4 hours/month	80% reduction

Timeline Reality (Medium Complexity Site: 1,000-5,000 pages)

• Week 1: Next.js setup, basic pages, routing (40 hours)
• Week 2: Data fetching conversion, API routes (50 hours)
• Week 3: Plugin migration, image handling (45 hours)
• Week 4: Testing, deployment, production setup (40 hours)
• Week 5: Post-launch fixes (20 hours) - ALWAYS BUDGET THIS

Total: 195 hours @ $75-125/hour = $14,625-$24,375

Cost Analysis (Monthly)

Gatsby operational costs: $2,440/month

• GitHub Actions: $340 (47-minute builds)
• Developer debugging: $1,500 (20 hours @ $75/hour)
• Failed deployment recovery: $600 (8 hours @ $75/hour)

Next.js operational costs: $620/month

• Vercel Pro hosting: $240
• GitHub Actions: $80 (4-minute builds)
• Developer maintenance: $300 (4 hours @ $75/hour)

ROI: 8.2 months payback period

Configuration

Critical Plugin Replacements

Gatsby Plugin	Next.js Replacement	Migration Effort
gatsby-plugin-sharp	next/image with custom processing	6-8 hours
gatsby-source-contentful	Custom Contentful API integration	4-6 hours
gatsby-plugin-local-search	Algolia or custom implementation	8-12 hours
gatsby-image	Manual next/image conversion	2-3 hours per 100 images

Data Fetching Conversion Pattern

// Gatsby GraphQL (automatic relationship resolution)
export const query = graphql`
  query ProductQuery($slug: String!) {
    contentfulProduct(slug: { eq: $slug }) {
      title
      relatedProducts { title slug price }
    }
  }
`;

// Next.js (manual API calls and relationship handling)
async function getProduct(slug: string) {
  const [contentfulData, shopifyData] = await Promise.all([
    fetch(`/api/contentful/products/${slug}`),
    fetch(`/api/shopify/products/${slug}`)
  ]);
  return { contentful: await contentfulData.json(), shopify: await shopifyData.json() };
}

Image Migration Critical Requirements

// Gatsby (automatic optimization)
<GatsbyImage image={product.featuredImage.gatsbyImageData} alt={product.title} />

// Next.js (manual configuration required)
<Image 
  src={product.featuredImage.url}
  alt={product.title}
  width={800}
  height={600}
  sizes="(max-width: 768px) 100vw, 800px"
  priority={index < 3}
/>

Critical Warnings

What Official Documentation Doesn't Tell You

• Plugin ecosystem replacement is mandatory - No Gatsby plugins work in Next.js
• GraphQL layer disappears - All data relationships must be manually resolved
• URL structure will change subtly - Trailing slashes, query parameters differ
• Images require complete rewrite - Every image needs manual width/height/sizes
• Production behaves differently - Caching, environment variables, routing all change

Production Day Disasters (Always Happen)

1. iOS Safari JavaScript failures - Different polyfill requirements
2. Form submissions break - Gatsby built-in forms vs Next.js API routes
3. Search functionality fails - Index generation method completely different
4. SEO rankings drop 8-23% - URL structure changes confuse Google crawlers
5. Image loading breaks - Double lazy-loading or missing optimization settings

Framework-Specific Gotchas

• Next.js App Router vs Pages Router: App Router is future but steeper learning curve
• Incremental Static Regeneration (ISR): Must be configured properly or content changes won't show
• Client-side routing: Gatsby preloads data on hover, Next.js doesn't by default
• Build vs runtime generation: Next.js generates pages on-demand vs Gatsby's pre-generation

Decision Criteria

When Migration Is Worth It

• Build times > 20 minutes consistently
• Memory crashes occurring weekly
• Plugin ecosystem abandoned (check GitHub activity)
• Team has React expertise
• Budget allows 4-6 weeks downtime
• Content publishing delays affecting business

When to Delay Migration

• Limited React expertise on team
• No budget for 200+ hours of work
• Complex custom plugin dependencies
• SEO rankings cannot tolerate temporary drops
• Active development on current site features

Alternative Framework Comparison

Framework	Timeline	Difficulty	Performance Gain	Ecosystem
Next.js	4-5 weeks	Medium	Build: 90% faster	Massive community
Astro	6-8 weeks	Hard	Build: 95% faster	Growing but smaller
Nuxt	5-7 weeks	Hard	Build: 85% faster	Vue ecosystem
Stay on Gatsby	0 weeks	Easy	Getting worse	Dead/abandoned

Resource Requirements

Expertise Prerequisites

• React proficiency: Essential for component conversion
• API integration experience: GraphQL to REST conversion
• DevOps knowledge: CI/CD pipeline reconfiguration
• SEO understanding: URL structure and redirect management

Time Investment Breakdown

• 40% Data fetching conversion - Most complex part
• 25% Plugin replacement - Research and implementation
• 20% Image and asset migration - Manual conversion work
• 15% Testing and debugging - Production edge cases

Hidden Costs

• CI/CD pipeline rewriting: 4-8 hours DevOps work
• Team training: 3-6 hours per team member
• Third-party integration updates: CMS webhooks, analytics setup
• Domain and hosting migration: Platform-specific optimization conflicts

Breaking Points & Failure Modes

Memory Exhaustion Patterns

• 4,000+ pages: Gatsby hits memory limits during build
• 7.2GB RAM usage: Typical failure point for createPages
• Exit code 137: JavaScript heap out of memory, build crashes

SEO Recovery Timeline

• Week 1: 8-23% traffic drop expected
• Week 2-4: Google recrawling and reindexing
• Month 1-3: Rankings stabilization for competitive keywords
• Permanent losses: Some high-competition rankings may never recover

Production Stability Issues

• First week: Production-only bugs (environment, caching)
• iOS Safari compatibility: Always requires separate debugging
• Form functionality: Built-in vs API route differences
• Search indexing: Complete rebuild required

Success Metrics & Validation

Build Performance Targets

• Build time reduction: 80%+ improvement expected
• Memory usage: <2GB peak vs Gatsby's 7GB+
• Success rate: 95%+ vs Gatsby's 50-60%
• Deploy frequency: Daily possible vs weekly with Gatsby

Business Impact Measurement

• Developer productivity: 16 hours/month time savings
• Content publishing speed: Minutes vs hours
• Infrastructure costs: 60-75% reduction
• Customer experience: Faster page loads, fewer failed deployments

This technical reference provides all operational intelligence needed for AI systems to understand implementation reality, failure modes, and decision criteria for Gatsby to Next.js migrations.