Using Next.js to Implement SSR and SSG: Which One to Choose?

When building modern web applications with Next.js, developers often face a crucial decision: should they use Server-Side Rendering (SSR) or Static Site Generation (SSG)? Both rendering strategies offer distinct advantages, and understanding their differences is key to making the right architectural choice for your project.

Understanding SSR and SSG in Next.js

Server-Side Rendering (SSR) generates HTML on the server for each request. In Next.js, you implement SSR by using getServerSideProps in your page components.

export async function getServerSideProps(context) {
  const res = await fetch(`https://api.example.com/data`);
  const data = await res.json();
 
  return { props: { data } };
}

Static Site Generation (SSG) generates HTML at build time. Next.js provides getStaticProps for static generation:

export async function getStaticProps() {
  const res = await fetch(`https://api.example.com/data`);
  const data = await res.json();
 
  return { props: { data }, revalidate: 60 };
}

When to Choose SSR

1. Frequently Updated Data: When your page displays data that changes often and needs to be up-to-date for every request
2. User-Specific Content: For pages that show personalized content based on cookies or authentication
3. SEO for Dynamic Content: When you need search engines to crawl content that changes frequently

When to Choose SSG

1. Performance Critical Applications: SSG pages load faster as they're pre-rendered and can be served via CDN
2. Content That Rarely Changes: For blogs, documentation, marketing pages, etc.
3. Better Scalability: Static files are easier to cache and distribute globally

Hybrid Approaches

Next.js allows combining both strategies in what's called Incremental Static Regeneration (ISR):

export async function getStaticProps() {
  const res = await fetch(`https://api.example.com/data`);
  const data = await res.json();
 
  return { 
    props: { data },
    // Re-generate the page at most once every 60 seconds
    revalidate: 60 
  };
}

This approach gives you the benefits of SSG with the ability to update content periodically without rebuilding the entire site.

Performance Considerations

• SSG: Faster initial page loads, better caching, lower server load
• SSR: Slower initial response (TTFB), but always shows fresh data
• ISR: Balances both, with fast cached responses and background updates

Making the Decision

Consider these factors when choosing:

1. Content Update Frequency: How often does your data change?
2. Traffic Patterns: Do you expect high traffic that would benefit from caching?
3. User Personalization: Does the content vary significantly per user?
4. SEO Requirements: How important is having the absolute latest content in search results?

For most applications, a combination of both approaches works best. Use SSG for most pages and SSR only where absolutely necessary. Next.js's flexibility allows you to mix both strategies on a page-by-page basis, giving you the optimal balance of performance and freshness.