Rendering Patterns at Scale: SSR, SSG, & ISR Architecture

When you start learning web development, you inevitably hit a wall of acronyms. You master HTML, CSS, and maybe get comfortable with JavaScript, but then someone asks, "Are you going to use SSR or SSG for that project?"

It feels like a trick question. You just want your website to show up on the screen, right? Why does it matter how it gets there?

The truth is, the decision between Server-Side Rendering (SSR) and Static Site Generation (SSG) is one of the most critical architectural choices you will make. It determines how fast your site loads, how much it costs to host, how Google ranks it, and even how it feels to the user.

In this guide, we are going to strip away the jargon. We won't be diving into complex compiler theory. Instead, we’ll look at these concepts through simple analogies and real-world examples. By the end, you’ll not only know what these terms mean, but you'll also have the confidence to pick the right one for your next big idea.

Introduction to Web Rendering

Before we can fight about which approach is better, we need to understand what "rendering" actually means in the context of the web.

In the simplest terms, rendering is the process of turning code (HTML, JavaScript, and data) into the visual page a user interacts with. It’s the translation from computer-speak to human-speak.

Imagine you have a blueprint for a house (your code) and a pile of lumber (your data). Rendering is the construction crew actually building the house so you can walk inside. The big question we are answering today is: When does the construction crew show up?

Do they build the house months in advance (SSG)? Or do they build the house in real-time the moment you pull into the driveway (SSR)?

Why Rendering Matters

You might be thinking, "As long as the user sees the page, who cares?"

But the timing of rendering changes everything. It impacts:

1. Speed (Performance): If the browser has to do all the work, the user stares at a white screen. If the server does the work, the user might wait for the server to reply.
2. SEO (Search Engine Optimization): Google's bots are smart, but they are also impatient. If your site takes too long to render or requires too much JavaScript to show text, Google might rank you lower.
3. User Experience: Have you ever visited a site where the layout jumps around as images load? That’s often a rendering issue.

Defining the Acronyms: SSR and SSG

Let’s get the dictionary definitions out of the way so we can move on to the fun stuff.

• SSR (Server-Side Rendering): This is the dynamic approach. When a user visits your URL, a server somewhere wakes up, fetches data, builds the HTML page specifically for that user, and sends it back. It happens on demand.
• SSG (Static Site Generation): This is the pre-built approach. You build all your pages on your computer (or a build server) before anyone even visits the site. The server just holds these pre-made files and hands them out like flyers. It happens at build time.

There is a third player often mentioned called CSR (Client-Side Rendering), which is what standard React apps do (rendering everything in the user's browser). While important, today we are focusing on the battle between the Server (SSR) and the Build Process (SSG).

Understanding Static Site Generation (SSG)

Let's start with Static Site Generation, often called the "Jamstack" approach. In recent years, this has become the darling of the web development world, and for good reason.

How SSG Works: The "Pre-Built" Approach

Imagine you run a daily newspaper.

Every morning at 4:00 AM, the printing press roars to life. It takes the stories written by journalists (the data) and the layout design (the code) and stamps them onto paper. By 6:00 AM, you have 10,000 identical copies of the newspaper.

When a customer walks up to a newsstand at 8:00 AM to buy a paper, the vendor doesn't have to write the stories or print the paper right then and there. They just hand over a copy from the stack. It is instantaneous.

This is exactly how SSG works.

1. Build Time: You run a command (like npm run build).
2. Data Fetching: Your build tool reaches out to your database or reads your markdown files to get the content.
3. HTML Generation: The tool generates an HTML file for every single page on your site. If you have a blog with 100 posts, it creates 100 HTML files.
4. Deployment: You upload these static files to a hosting provider.
5. Request Time: When a user visits yoursite.com/blog/post-1, the server simply hands them the post-1.html file. No thinking required.

Because the HTML is already made, the browser can display it immediately.

Key Advantages of SSG

1. Blazing Fast Performance

Since the server doesn't have to "think" or run any logic when a user visits, the response time is incredibly fast. It's just moving a file from a hard drive to the internet. You can also put these files on a CDN (Content Delivery Network), which puts copies of your site on servers all over the world. If a user visits from London, they get the file from a London server, not one in New York.

2. Unbreakable Security

With SSR or traditional databases, your server is constantly running code and talking to databases. This opens up potential security holes—what if someone tricks the server into running bad code?

With SSG, there is no running server code. It’s just files. You can't "hack" a static HTML file any more than you can hack a PDF on your desktop. This drastically reduces the surface area for attacks.

3. Cheap Hosting

Hosting static files is the cheapest thing you can do on the internet. You don't need a powerful server with lots of RAM or CPU. You can host an SSG site for free on platforms like Vercel, Netlify, or GitHub Pages.

Limitations of Static Generation

So, if it's fast, secure, and cheap, why doesn't everyone use it?

1. The "Build Time" Bottleneck

Remember the newspaper analogy? What happens if you have breaking news at 10:00 AM? You can't just change the papers already in people's hands. You have to stop the presses, print a whole new batch, and redistribute them.

In SSG, if you fix a typo or publish a new article, you have to rebuild the entire site. If you have 100 pages, this takes seconds. If you have 100,000 pages, a rebuild could take hours. This makes SSG bad for sites that update constantly (like a news ticker or a social media feed).

2. Stale Data

Between builds, your data is "stale." If your site shows "Stock Availability: 5 items left," and someone buys one, the site will still say "5 items left" until you rebuild and redeploy the site.

Ideal Use Cases for SSG

SSG is the perfect choice for content that doesn't change every minute.

• Personal Blogs: You write an article, publish it, and it stays the same forever.
• Documentation Sites: Technical docs are updated occasionally, not every second.
• Marketing Landing Pages: These pages are usually static and need to be extremely fast for SEO.
• Portfolios: Your list of projects rarely changes.

Understanding Server-Side Rendering (SSR)

Now, let's look at the heavyweight champion of the dynamic web: Server-Side Rendering. This is how the web worked traditionally (think PHP or Ruby on Rails), but modern frameworks like Next.js and Nuxt have reinvented it.

How SSR Works: The "On-Demand" Approach

Let’s swap our newspaper analogy for a restaurant kitchen.

When you go to a restaurant, there isn't a stack of pre-cooked steaks waiting on the counter (hopefully). Instead, you sit down and place an order.

1. Request: You order a steak (User requests a URL).
2. Processing: The waiter takes the ticket to the kitchen. The chef checks the fridge for ingredients (Server fetches data from the database).
3. Cooking: The chef cooks the steak exactly how you asked for it—medium rare, side of fries (Server builds the HTML page).
4. Service: The waiter brings the hot plate to your table (Server sends HTML to the browser).

Every single time a user visits a page, this entire process happens from scratch.

Key Advantages of SSR

1. Always Fresh Data

Because the page is built the moment the user asks for it, the data is never stale. If you are building a stock trading dashboard or a sports score site, SSR ensures the user sees the exact price or score at that specific second.

2. Dynamic Personalization

SSG gives everyone the same page. SSR can give everyone a unique page.

Because the server builds the page after the request comes in, it knows who the user is (via cookies or headers). It can render "Welcome back, Sarah!" or hide content based on user permissions.

3. Great SEO for Dynamic Content

Search engines like Google need to see the content to rank it. In the past, Client-Side Rendering (CSR) was bad for SEO because the page was empty until JavaScript ran. SSR solves this by sending fully formed HTML to the bot, just like SSG, but it can do it for millions of dynamic pages that would be impossible to pre-build.

Limitations of Server-Side Rendering

1. Slower Time to First Byte (TTFB)

The user has to wait. They have to wait for the server to fetch data, wait for the server to generate HTML, and then wait for the response. Even if this only takes 500ms, that is 500ms longer than SSG. Optimizing this often requires deep knowledge of React Performance.

2. Server Costs and Complexity

You need a server running 24/7. If 1,000 users visit your site at the exact same second, your server has to cook 1,000 meals at once. This requires more CPU and memory, which costs more money. If you get a massive spike in traffic (the "Reddit hug of death"), your server might crash if it can't scale up quickly enough.

Ideal Use Cases for SSR

SSR is necessary when "static" just isn't enough.

• Social Media Feeds: Twitter or Facebook cannot be static; the content changes every second.
• E-commerce Storefronts: Prices, inventory, and personalized recommendations change constantly.
• User Dashboards: Any page behind a login screen usually needs SSR (or CSR) because it is unique to that user.
• Forums and Comment Sections: You want to see new comments immediately without waiting for a 10-minute site rebuild.

Head-to-Head Comparison

Now that we understand the players, let's put them in the ring together.

Performance and Page Load Speed

• SSG: The clear winner. You are serving a static file. It is the digital equivalent of handing someone a flyer. It loads instantly.
• SSR: Usually slower. The server has work to do before it can respond.

However, modern SSR is getting faster. By using intelligent caching strategies (where the server remembers the result of the last request for a few minutes), SSR can get close to SSG speeds. But out of the box? SSG wins.

SEO Implications for Beginners

If you are a beginner, you might hear "SSR is better for SEO." That is a half-truth.

Both SSG and SSR are excellent for SEO.

Google loves HTML. Both methods provide full HTML to the search bot immediately. The bot doesn't care if the HTML was made 3 weeks ago (SSG) or 3 milliseconds ago (SSR). It just wants to read the text.

The only time SSR wins on SEO is for massive sites. If you have 5 million product pages, you physically cannot pre-build them all with SSG (the build would take weeks). SSR allows those pages to exist without cluttering up your build pipeline.

Server Costs and Maintenance

• SSG: "Set it and forget it." Once you deploy, the files just sit there. It’s free or very cheap. There is no server maintenance because there is no server to maintain.
• SSR: Requires monitoring. Is the server up? Is the database responding? Did a memory leak crash the process? You are responsible for the infrastructure (or paying a cloud provider like AWS or Vercel to manage it for you).

How to Choose for Your Project

You are staring at your code editor, ready to start npx create-next-app, and you need to make a choice. Here is the mental framework I use.

Analyzing Your Data Needs

Ask yourself this simple question: "Can I predict what this page will look like before the user asks for it?"

• Yes: Use SSG.
  • Example: A blog post. I know the title and body text before anyone reads it.
• No: Use SSR.
  • Example: A search results page. I have no idea what the user will type into the search bar, so I can't pre-build the results.

The "Personalization" Factor

Does the page look the same for everyone?

• If User A and User B see the exact same content -> SSG.
• If User A sees "My Profile" and User B sees "Login" -> SSR (or Client-Side Rendering).

Note: There is a hybrid approach. You can use SSG for the main shell of the page (header, footer, layout) and then use Client-Side JavaScript to fetch the personalized bits (like the user's avatar) after the page loads. This is often the "best of both worlds" for beginners.

Conclusion

Choosing between SSR and SSG used to be a rigid decision. You picked a framework (like Jekyll for SSG or Express for SSR) and you were stuck with it.

Today, frameworks like Next.js, Nuxt, and SvelteKit allow you to mix and match. You can have your "About Us" page use SSG for speed, and your "Account Dashboard" use SSR for data freshness.

Final Recommendations

If you are just starting out, here is my advice:

1. Default to SSG. It is simpler, cheaper, and faster. Most beginner projects (portfolios, blogs, landing pages) fit perfectly here.
2. Move to SSR only when necessary. If you realize you need real-time data or secure content behind a login, then switch those specific pages to SSR.

Don't over-engineer your first project. A fast static site is better than a slow, complex dynamic one.

Building for the web is about trade-offs. SSG trades build time for runtime speed. SSR trades server resources for data freshness. Understanding these trade-offs is what separates a coder from a software engineer.

Now, go build something awesome—whether you pre-cook it or cook it to order!

Frequently Asked Questions

Can I mix SSR and SSG in the same project? Yes! Modern frameworks like Next.js allow you to choose the rendering method on a per-page basis. You can statically generate your marketing pages while server-rendering your checkout flow.

Is SSR better for SEO than SSG? Generally, no. Both are excellent for SEO because they serve fully rendered HTML to search crawlers. SSR is only "better" if you have content that updates very frequently and needs to be indexed immediately.

Do I need a database for SSG? Not necessarily. SSG is often used with Markdown files (where your content lives in text files). However, you can use a database (like a Headless CMS) as the source of truth, pulling that data only during the build process.

What happens if I use SSG and need to update a typo? You must trigger a new "build" of your site. This usually takes a few minutes depending on the size of your site. Once the build finishes and deploys, the typo is fixed.

Which is cheaper to host? SSG is significantly cheaper. Since it relies on static files, it can be hosted on CDNs, often for free on hobby tiers. SSR requires active server computation, which incurs costs as traffic scales.