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CDNS DON’T FIX WEB VITALS — NETFLIX LEARNED THIS THE HARD WAY
This isn’t a CDN problem — it’s an architectural one. In this guide, we’ll break down why CDNs fail Web Vitals, what real companies discovered the hard way, and how to fix performance at the system level instead of chasing Lighthouse scores.
Hiteshkumar solanki
February 13, 2026
Why CDN Isn't the Magic Solution You Think It Is
Hey, welcome back to BeyondIT. Today we're going to discuss the biggest misunderstanding or lie of the web development industry: "Considering CDN as a set-and-forget solution for web performance".
While 72% of global internet traffic is handled by CDNs, completely relying on CDN for performance optimization is a fallacy. Let's break this down with data.
According to the study "The limited impact of CDN on modern web performance" (University of Washington 2023), they A/B tested 10,000 websites. The study concluded that CDN can improve metrics by only 15%, but 85% of performance gains come from:
Server-Side Optimization (40%)
Client-Side Optimization (35%)
Asset Optimization (10%)
Netflix Case Study: When CDN Isn't Enough
Netflix was using the best CDN architecture, but Netflix engineers found that despite CDN, Time-To-Interactive (TTI) was suffering. The issue was not about CDN or delay in serving files. The issue was hydrating React components on their logged-out page.
Now, the solution was not to upgrade the CDN tier because it cannot solve the issue.
What Netflix Did:
Netflix removed React from the signup page and replaced it with vanilla JavaScript
It drastically reduced client-side JavaScript by 200KB
It improved Time-To-Interactive by 50%
The Conclusion: If your application logic is bloated, CDN cannot act as a magical tool and improve the performance metrics.
Web Vitals Re-Explained — The Infrastructure vs. Architecture Gap
The reality is that we consider Core Web Vitals as a scorecard to rank in Google's algorithm. This is the main issue—we never consider it as a measurement tool for friction our users face while accessing our websites.
The role of CDN is to transfer files from server to client as fast as possible. The execution of those files on the client side cannot be optimized using CDN.
Let's understand the three core pillars of Core Web Vitals and why CDNs fail to optimize them.
1. LCP (Largest Contentful Paint): The Render-Blocking Trap
We think that if we put our hero image on a CDN, LCP will be fast. In 2026, network speed and delivery is not the main issue—the main issue is resource prioritization.
Your CDN can serve the image in 50ms, but what if large JavaScript blocks the browser from parsing the HTML that requests the hero image? The problem of LCP will remain as it is.
CDN can solve the issue of improving Resource load time, but it cannot solve the issue of Resource load delay.
Airbnb Case Study
Airbnb found that their LCP was stagnating at 4.2 seconds, despite using a sophisticated CDN setup. Their hero image was delivered from CDN but still was not rendering early.
ISSUE: The image was getting delivered first but was getting buried under heavy client-side JavaScriptexecution.
SOLUTION: They just implemented priority hints (fetchpriority="high"). Yes, it was this simple—now the browser prioritizes the hero image and LCP dropped to 2.1 seconds.
IMPACT: LCP dropped to 2.1 seconds and 12% increase in bookings.
Lesson: Understand LCP as Four Components
Time to First Byte (TTFB) — CDN can optimize it
Resource load time — CDN can optimize it
Resource load delay — CDN cannot optimize it
Element Render Delay — CDN cannot optimize it
If your LCP is high, don't just focus on CDN—try to optimize the resource load delay and element render delay as Airbnb did.
2. INP (Interaction to Next Paint): The Hidden Business Killer
"My site loads fast, so it is fast"—But no. A site can load fast but may be unresponsive for a brief time because of a blocked main thread.
In simple words, it measures the time delay between each click, tap, keystroke, and response. It is the time when the browser was frozen, executing JavaScript and delaying input execution.
Simply, it cannot be solved by CDN. CDN delivers JavaScript files fast, but it cannot execute them fast for you.
Case Study: Shopify's Checkout Investigation
Shopify found that their checkout button had an INP of 450ms. In the world of e-commerce, a half-second delay can lead to abandoned carts and huge revenue loss.
ISSUE: A third-party fraud detection script was blocking the main thread, causing the checkout button to be non-responsive for 450ms.
SOLUTION: They moved the fraud detection logic off the main thread using Web Workers. They also used a third-party library called "Partytown" which relocates resource-intensive scripts to the background.
RESULT: INP improved by 120ms and 7% reduction in cart abandonment.
Lesson Learned: Yield the Main Thread
We need to break up long tasks (generally over 50ms) using setTimeout() or scheduler.yield(). Try to offload non-UI logic to Web Workers for more efficiency.
3. CLS (Cumulative Layout Shift): The Revenue Leech
Generally, we think layout shift is just a visual annoyance. In reality, they reflect the sign of race conditions in the rendering path. They directly impact revenue.
CLS happens when visible elements change after initial rendering. In most cases, dynamic content like advertisements and hydration causes CLS.
Case Study: Wayfair's Revenue Impact Study
Wayfair conducted an elaborate study on the relation between CLS and revenue impact. According to the study, 0.1 increase in CLS led to 1.2% loss in revenue.
ISSUE: Dynamic ad loading and promotional banner loading were causing CLS of 0.45.
SOLUTION: They implemented strict container reservation (setting explicit width and height for containers). They also used size negotiation APIs to ensure ads fit their defined container size.
RESULT: The CLS dropped to 0.02, and they recovered around $2.4 million monthly revenue.
Lesson Learned: Your CDN Can Worsen CLS
If the CDN delivers assets in unpredictable order, it can worsen CLS. You have to manage layout stability at the CSS level. Ensure all images and embeds have explicit dimensions and use font-display: swap carefully to prevent text reflows.
