Migrating a Major News Site to Arc XP With SSR React
What we learned leading a CMS migration and React replatform for a high-traffic news property — content mapping, performance at scale, and the organizational challenges of a live migration.
CMS migrations for high-traffic news properties are among the highest-stakes engineering projects in digital media. The site must stay live throughout. Editorial workflows can’t break. The SEO equity of thousands of legacy URLs is at stake. And the clock is always ticking — news doesn’t stop while you migrate.
Why Arc XP
Arc XP is The Washington Post’s cloud-native publishing platform, built specifically for digital news. It provides content management, composing tools, subscriptions, commerce, and a CDN-delivered page rendering layer — all as a managed service.
The key architectural feature: Arc separates content (managed in their CMS) from presentation (your React components). You own the rendering layer; Arc owns the content storage, CDN, and delivery infrastructure.
Content Mapping Strategy
Content migration is fundamentally a mapping problem. Your legacy content has a structure. Arc XP’s Ans (Arc Native Specification) format has a different structure. You need to transform every piece of content from one to the other.
The process we followed:
Step 1: Content inventory. How many articles, images, galleries, author profiles, and section pages exist? A complete count surfaces edge cases before migration scripts run.
Step 2: Field mapping. For each content type, map every field to its Arc equivalent. Some fields map directly (headline → headlines.basic). Others require transformation (a legacy HTML body → Arc’s rich content blocks). Others have no equivalent and require a decision: migrate with data loss, or create a custom field?
Step 3: Script and validate. Write migration scripts that transform and import. Run them on a subset of content. Compare the output to the original manually. Check URL slugs, SEO metadata, image references, and author associations.
Step 4: Migrate incrementally. Don’t migrate everything at once. Migrate by content type: authors first (no dependencies), then articles (depends on authors and images), then galleries, then section pages.
SSR React at News Scale
Arc XP’s rendering layer (Fusion Engine) runs your React components server-side on their infrastructure. The performance implications differ from a self-hosted SSR setup.
Critical patterns for news SSR performance:
Component-level caching. Heavily shared components (navigation, subscription CTAs, ad slots) should cache aggressively. News articles are mostly static after publication — their components should be cacheable for minutes.
Content-size awareness. A breaking news article may have 10 content blocks. A longform investigation may have 200. Components that iterate over content blocks need to handle both efficiently. Memoize expensive renders.
Above-the-fold priority. The hero content (headline, lede, hero image) renders first and contributes to LCP. Everything below the fold can defer. Arc’s component system supports render prioritization.
URL Preservation and SEO
Legacy news sites have years of inbound links, social shares, and search indexing. 404ing those URLs is burning accumulated SEO equity.
The redirect strategy:
- 301 permanent redirects for every URL that exists in the legacy system
- Canonical tags on migrated content pointing to the new canonical URL
- The sitemap updated immediately post-migration
- Google Search Console monitoring for crawl errors in the first 30 days
We tracked organic search traffic weekly for 90 days post-migration. Some rank fluctuation is expected during any large migration; sustained drops indicate crawling or indexing problems that need investigation.
The Editorial Workflow Transition
The human side of CMS migration is as hard as the technical side. Journalists who’ve used the same CMS for a decade have muscle memory for how it works. Training on a new CMS while the news cycle continues is brutal.
The approach that worked: staged rollout. A small group of reporters and editors were early adopters for three weeks before the full migration. They became internal experts, documented quirks specific to the newsroom’s workflow, and helped train everyone else.
No CMS switch during a major news event. Build in a quiet news period window if possible. Avoid election weeks, major sporting events, and scheduled major announcements.