Server-Side Rendering (SSR) vs. Static Site Generation (SSG) in Next.js

In the world of modern web development, ensuring fast load times and a seamless user experience is paramount. Next.js, a powerful React framework, has emerged as a go-to solution for developers looking to build high-performance web applications. One of the key features that make Next.js so versatile is its support for multiple rendering methods, including Server-Side Rendering (SSR) and Static Site Generation (SSG). Understanding these two approaches—and knowing when to use each—can significantly enhance your application's performance and scalability.

What is Server-Side Rendering (SSR)?

Server-Side Rendering (SSR) is a method where the HTML for a page is generated on the server for each request. This means that every time a user requests a page, the server generates the HTML, sends it to the client, and then the client’s browser renders the page. This approach ensures that the content is up-to-date at the time of the request.

How SSR Works in Next.js

In Next.js, SSR can be implemented using the getServerSideProps function. This function is executed on the server at runtime and allows you to fetch data on the server before rendering the page. Here's a basic example:

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

  return { props: { data } };
}

function Page({ data }) {
  return (
    <div>
      <h1>Data from SSR</h1>
      <pre>{JSON.stringify(data, null, 2)}</pre>
    </div>
  );
}

export default Page;        

In this example, getServerSideProps fetches data from an external API on each request, ensuring the page is rendered with the latest information.

Advantages of SSR

• Fresh Content: Since the HTML is generated on each request, the content is always up-to-date.
• SEO-Friendly: SSR provides fully rendered HTML to the client, which is beneficial for search engines and social media platforms that scrape page content.
• Personalization: SSR is ideal for pages that require personalization or user-specific data, such as dashboards or user profiles.

Drawbacks of SSR

• Performance: Because the server must generate the HTML on each request, SSR can be slower compared to other rendering methods, especially under high traffic.
• Scalability: SSR puts more load on the server, making it less scalable than static methods, especially for large-scale applications.

What is Static Site Generation (SSG)?

Static Site Generation (SSG) is a method where the HTML for a page is generated at build time, not on each request. The generated HTML files are then served directly from a CDN or a web server, making the page load extremely fast. SSG is ideal for pages where the content doesn’t change often.

How SSG Works in Next.js

In Next.js, SSG can be implemented using the getStaticProps function. This function runs at build time and generates static HTML for the pages. Here’s an example:

export async function getStaticProps() {
  const res = await fetch(`https://api.example.com/data`);
  const data = await res.json();

  return { props: { data } };
}

function Page({ data }) {
  return (
    <div>
      <h1>Data from SSG</h1>
      <pre>{JSON.stringify(data, null, 2)}</pre>
    </div>
  );
}

export default Page;        

In this example, getStaticProps fetches data during the build process, and the HTML is generated as static files. These files are then served to users whenever they request the page.

Advantages of SSG

• Performance: Since the HTML is pre-generated and served as static files, SSG offers extremely fast load times.
• Scalability: SSG scales well because static files can be served from a CDN, reducing the load on the server.
• SEO-Friendly: Like SSR, SSG provides fully rendered HTML to the client, which is great for SEO.

Drawbacks of SSG

• Stale Content: Since the HTML is generated at build time, the content may become outdated if the data changes frequently.
• Limited Use Cases: SSG is not ideal for pages that require real-time data or personalization.