SSG vs SSR – Understanding the Core Differences in Modern Web Rendering

 

SSG vs SSR – Understanding the Core Differences in Modern Web Rendering

In today’s frontend development landscape, especially with frameworks like Next.js, Nuxt.js, and Gatsby, rendering strategies like Static Site Generation (SSG) and Server-Side Rendering (SSR) are central to performance and SEO. While both render HTML before it reaches the browser, their workflows and ideal use cases differ significantly.

This article explores how SSG and SSR work internally, their advantages and drawbacks, and provides a detailed flow for each rendering strategy.

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What is Static Site Generation (SSG)?

SSG is a rendering strategy where HTML pages are generated at build time. This means that the content of your website is compiled into static HTML files before deployment and then served as-is to the users.

How SSG Works – Flow Breakdown

1. Developer Initiates Build
   A build command is run (e.g., next build, gatsby build).

2. Data Fetching Happens During Build Time
   Any dynamic content from APIs, CMSs, databases, or markdown files is fetched.

3. HTML Files Are Generated
   Each route is pre-rendered into a complete HTML file with the required data embedded.

4. Static Files Are Deployed
   These files are uploaded to a CDN or static host (like Vercel, Netlify, or S3).

5. Client Requests the Page
   When a user visits the page, the pre-rendered HTML is delivered instantly from the CDN without any backend logic.

Advantages of SSG

• Fast page loads due to CDN caching

• Minimal server costs and high scalability

• Excellent SEO support

• No need for backend processing per request

Limitations of SSG

• Content is only as fresh as the last build

• Long build times for large sites

• Requires rebuilding and redeployment for updates (unless using Incremental Static Regeneration)

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What is Server-Side Rendering (SSR)?

SSR refers to rendering HTML on the server at the time of each request. Every time a user visits the page, the server compiles and sends a fully rendered HTML document using up-to-date data.

How SSR Works – Flow Breakdown

1. User Requests the Page
   A browser sends a request to the server when the user visits a route.

2. Server Fetches Data at Runtime
   API calls, database queries, or CMS content are fetched on-demand.

3. HTML Is Rendered on the Server
   The server uses a rendering engine (React, Vue, etc.) to assemble HTML with the fetched data.

4. Server Sends HTML to Client
   The browser receives the rendered HTML and displays it immediately.

5. Hydration of JavaScript on Client
   JavaScript takes over the static HTML to make it interactive.

Advantages of SSR

• Always serves fresh, up-to-date content

• Ideal for pages that rely on real-time or personalized data

• Strong SEO capabilities

Limitations of SSR

• Slower response times compared to SSG

• Requires backend infrastructure to handle requests

• More resource-intensive on the server under heavy traffic

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Comparative Table – SSG vs SSR

Feature	SSG	SSR
Rendering Time	Build time	Request time
Page Speed	Very fast (CDN cached)	Slower (depends on server processing)
Content Freshness	May become stale	Always fresh
Scalability	Highly scalable	Server load increases with traffic
Hosting	Static hosting/CDN	Requires server runtime
Personalization	Limited (pre-rendered)	Fully supported
SEO	Excellent	Excellent
Best Use Cases	Blogs, documentation, landing pages	Dashboards, news feeds, product pages

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When Should You Use SSG or SSR?

Use SSG when:

• Your content does not change often.

• You want maximum speed and scalability.

• You can afford to rebuild the site for updates.

Use SSR when:

• Your content changes frequently.

• You need real-time data.

• Personalization or user-specific rendering is required.

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Hybrid Approach

Frameworks like Next.js support a hybrid model where both SSG and SSR can be used in the same application. For example, marketing pages can be built using SSG while user dashboards can use SSR.

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Final Thoughts

Understanding the distinction between SSG and SSR is critical when architecting modern web applications. While SSG offers unbeatable speed and cost-efficiency for static content, SSR shines in dynamic and personalized experiences. Evaluate your project’s needs—content freshness, performance, personalization, scalability—and choose the rendering method that best aligns with your goals.