Site Migrations

A migration is any change that alters URLs, rendering or domain: redesigns, CMS or framework swaps, domain changes, HTTP to HTTPS, consolidating sites. It is the highest-stakes routine operation in SEO. Done well, traffic dips slightly for a few weeks; done badly, years of accumulated equity evaporate in a deploy. The difference is process.

The iron rules#

1. Every old URL gets a response plan. Redirect (301 or 308) to its closest equivalent, or a deliberate 410. No mass 404s, no "the homepage will catch it."
2. Redirect to equivalents, not the homepage. Blanket homepage redirects are treated as soft 404s, so equity evaporates anyway.
3. One change at a time when possible. Domain + design + platform + content all at once means when traffic drops, you cannot isolate why.
4. Measure before, so you can verify after.

Phase 1: Inventory (before anything else)#

Build the complete list of URLs that matter from a full crawl, Search Console (everything with impressions in the last 16 months), analytics (everything with sessions), sitemaps and your backlink tool (everything with external links). Union these; the result is your migration universe. For each URL, record current clicks, conversions and linking domains. That is your baseline and your prioritization weight.

Also record the non-URL settings that tend to get lost: robots.txt rules (including AI crawler rules), CDN bot settings, hreflang, structured data, and Search Console settings such as the Search generative AI control.

Phase 2: The redirect map#

A spreadsheet (or generated file) mapping every old URL to its new home:

old_url,new_url,type
/blog/2019/05/seo-tips,/guides/seo-basics,301
/products.php?id=42,/products/ergo-chair,301
/old-category/,/new-category/,301
/discontinued-thing,(410 gone),410

Rules of thumb:

• Pattern-redirect where structure allows (/blog/:year/:month/:slug → /guides/:slug), and itemize the exceptions.
• No chains: old → new directly, including fixing existing old redirects to point at the final destination.
• Equivalence by intent: the new URL should satisfy the same query.

In Next.js, bulk redirects live in config:

async redirects() {
  return [
    { source: "/blog/:year/:month/:slug", destination: "/guides/:slug", permanent: true },
    { source: "/products.php", destination: "/products", permanent: true },
  ];
},

permanent: true sends a 308, which Google treats like a 301. For very large maps, look the redirect up at the edge or in Next.js's proxy (formerly middleware) from a key-value store rather than shipping thousands of static entries.

Phase 3: Pre-launch on staging#

Audit the new site as if it were a stranger's (audit playbook): crawl it, verify titles, canonicals, structured data and rendered content against production. Then test the redirect map against staging with a script: fetch every old URL and assert a one-hop 301 or 308 to the mapped target.

Phase 4: Launch day#

□ robots.txt correct on production (no staging disallow!)
□ noindex absent from production templates
□ CDN/WAF bot rules carried over (search and AI search bots allowed)
□ Redirect map live: spot-check top-100 old URLs
□ New sitemap submitted in Search Console; old sitemap left up briefly
  (it helps engines discover the redirects faster)
□ Domain change? → Change of Address tool for EVERY variant
  (www and non-www), plus Bing Webmaster Tools Site Move
□ Canonicals point to new URLs (not old, not staging)
□ Analytics + Search Console verified on the new property
□ Annotation added on the Search Console chart for launch day
□ Internal links updated to final URLs (not riding redirects)

Phase 5: Monitor and stabilize#

Expect temporary flux, from days to a few weeks, while engines reprocess. Google's canonicalization docs (July 2026) note it may hold pages in a duplicate cluster for up to two weeks after fixes. Watch daily at first:

• Search Console Page indexing on both properties: old URLs should drain as "Page with redirect", new ones fill the index.
• Crawl stats: a spike is normal (Google revisiting everything); sustained 404 spikes are your gaps. Patch the redirect map as they surface.
• Traffic by section vs your Phase 1 baseline: section-level losses point at section-level mistakes (a template's canonical, a missed pattern).
• Server logs: Googlebot hitting old URLs and getting anything other than a 301 means more work.

Keep redirects live for as long as possible: Google's site move guidance says generally at least a year, and link equity keeps flowing through them for as long as external links point at old URLs. Judge success at +90 days against pre-migration clicks and conversions, not against the post-launch dip.

Next: E-commerce SEO, where migrations, faceted navigation and product data meet.