How does getServerSideProps work internally? What is its execution context?

Internally, getServerSideProps is a Next.js function designed for Server-Side Rendering (SSR) that runs exclusively on the server at request time. When a request hits a page with getServerSideProps, Next.js executes this function first, providing it with rich context about the request. The function can perform any server-side operations—database queries, API calls, authentication checks—and must return a serializable object. Next.js then uses the returned props to render the React component to HTML on the server, sending the fully-formed page to the client. This entire process happens synchronously per request, ensuring the page always reflects the latest data.

When a request arrives, Next.js checks if the page exports getServerSideProps. If yes, it enters SSR mode: First, it calls getServerSideProps with the context object populated from the request. The function executes in a Node.js environment with full server capabilities—direct database access, file system operations, or internal API calls are all safe here because this code never reaches the client. Next.js then awaits the returned promise, expecting an object with props, notFound, or redirect. If props are returned, Next.js serializes them with JSON.stringify and passes them to the page component for rendering on the server. The complete HTML is generated and sent to the client, with the props also embedded in a script tag for hydration.

When users navigate between pages using next/link or next/router, getServerSideProps still runs on the server, but the mechanism differs slightly. Next.js makes a lightweight API request to _next/data/development/{url}.json (or production equivalent) which triggers getServerSideProps execution and returns only the JSON props, not the full HTML. The client then uses these props to render the page without a full reload, maintaining SPA-like navigation while still fetching fresh data per request. This is why you can't have loading states inside getServerSideProps—it's a blocking function that must complete before navigation finishes.

Choose getServerSideProps when you absolutely need request-time data—authenticated content, personalized pages, or data that changes faster than you can rebuild. It's perfect for dashboards, user profiles, and any page where the content is different for every visitor. However, for public content that changes less frequently, prefer getStaticProps with ISR—you'll get similar freshness with much better performance and lower server costs. And if the page doesn't need initial data at all, consider client-side fetching after a static shell for the best balance of performance and freshness.