The browser only talks to one server — composing Marko, React, and Riot into one hotel page

You open a hotel page. It looks like one product: a search grid, a featured stay, local highlights, reviews, a sticky trip summary. Under the hood it is eight HTTP servers and three UI runtimes . That is the experiment behind HarborStay , a demo booking app I built to answer a stubborn question: Can independent teams ship independent UI, in independent frameworks, and still give the browser a single, paint-ready HTML page? The punchline: yes — if the shell never imports a component. It only fetches HTML. The one rule The browser never talks to a fragment. It talks to the composer on port 3100 . The composer owns routes, layout, and the booking flow. Everything else is a fragment server that returns a chunk of HTML. flowchart LR Browser["Browser"] --> Composer["Composer :3100"] subgraph fragments["Fragment servers"] Nav["Navigation Marko :3101"] Search["Hotel search Marko :3102"] Details["Hotel details Marko :3103"] Reviews["Reviews Marko :3104"] Recs["Recommendations Marko :3105"] Highlights["Local highlights React :3106"] Disco["Experiences discovery Riot :3107"] Itin["Experiences itinerary Riot :3108"] end Composer --> Nav Composer --> Search Composer --> Details Composer --> Reviews Composer --> Recs Composer --> Highlights Composer --> Disco Composer --> Itin Composer --> CDN["CDN :3200"] This is the opposite of the usual microfrontend story (Module Federation, shared React, a host that import() s widgets). HarborStay is HTML composition . The shell does not know whether a fragment was rendered by Marko, React, or a hand-rolled Riot string. It only knows a URL. That one constraint buys a lot: Fragment teams can pick a runtime without asking the shell. A fragment outage becomes a fallback box, not a blank page. You can deploy search without redeploying reviews. It also forces honesty. If two fragments need to share a Redux store, the architecture is already leaking. What the user actually sees HarborStay models a small premium catalog: Harbor View Lodge in Lisbon