CDN
Introduction
This chapter examines the rapidly evolving landscape of Content Delivery Networks (CDNs) in 2025, with an increased focus on their role in HTTP protocol optimization. CDNs fundamentally exist to solve HTTP delivery challenges at scale, from reducing TCP connection overhead through HTTP/2 multiplexing to eliminating head-of-line blocking via HTTP/3’s QUIC transport. As HTTP protocols have evolved from HTTP/1.1’s connection limitations to HTTP/3’s advanced features, CDNs have served as the primary deployment vehicle, implementing these protocols years before origin servers adopt them.
Modern CDNs optimize delivery across the entire spectrum of web content. For highly cacheable resources (static assets, public API responses, shared content), CDNs provide traditional caching benefits enhanced by advanced compression and modern format delivery. For content with limited cacheability (user-specific data, frequently updated APIs, personalized experiences), CDNs still deliver performance improvements through connection optimization, intelligent routing, and edge processing, reducing latency even when content cannot be cached.
Building upon our comprehensive analysis from 2024, our 2025 analysis reveals shifts in protocol adoption and optimization strategies. A key focus of this chapter is the maturation of HTTP/3 adoption, the rise of modern optimization techniques like Server-Timing transparency, and the sophisticated multi-layered approaches CDNs are taking to performance, security, and user experience.
What is a CDN?
A Content Delivery Network (CDN) is a geographically distributed network of servers designed to provide high availability, enhanced performance, and improved security for web content and applications. The primary goal of a CDN is to minimize latency and optimize content delivery by serving data from locations closer to the end user.
CDNs serve as intermediary infrastructure between end users and origin servers, intercepting web requests and optimizing the complete delivery process. To understand how CDNs can enhance web performance, consider the traditional web interaction when a user types a hostname into a browser, and how different CDNs may improve each step:
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DNS Resolution
- Traditional: Browser queries DNS for origin server IP, often with slow resolution times
- CDN Processed: CDN DNS infrastructure may use various routing strategies (anycast or unicast) to direct users to optimal edge servers. Some CDNs support modern DNS records like HTTPS or SVCB (Service Binding) records that can advertise protocol capabilities directly in DNS responses, though adoption varies across providers
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Connection Establishment
- Traditional: Browser establishes new TCP connection to distant origin server with full handshake overhead
- CDN Processed: Connection to nearby edge server over TCP (for HTTP/1.1 and HTTP/2) or UDP with QUIC (for HTTP/3). CDNs may support HTTP/3’s 0-RTT connection resumption for returning visitors, though not all CDNs have implemented these newer connection optimization features
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Protocol Negotiation
- Traditional: Limited to origin server’s protocol capabilities, often older HTTP versions
- CDN Processed: Many CDNs can advertise modern protocol availability through
Alt-Svc(Alternative Service) HTTP headers that inform browsers about alternative protocols. CDNs typically provide protocol translation benefits, accepting newer protocols from browsers while maintaining connections to origins, regardless of origin server capabilities
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Request Processing & Optimization
- Traditional: Basic request forwarding with minimal processing
- CDN Processed: Depending on the CDN, may include header normalization, intelligent routing decisions, addition of performance headers like Server-Timing which provides server-side performance metrics, security headers, and request optimization based on content type and user geographic location
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Response Processing
- Traditional: Direct response from origin server, limited by origin’s HTTP server capabilities
- CDN Processed: CDNs may implement advanced caching strategies, cache validation, Content-Encoding optimization (such as Brotli or Gzip compression), conditional request support (like 304 Not Modified responses that save bandwidth), and response transformation, though specific features vary by provider
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Connection Management
- Traditional: Single connection per request or basic keep-alive to origin
- CDN Processed: Many CDNs implement dual-sided connection optimization, maintaining persistent connections to clients while using intelligent connection pooling to origin servers, reducing overhead on both ends
CDNs serve as deployment platforms for emerging web standards, implementing new HTTP headers, compression algorithms, and security features at scale before they become widely adopted by origin servers. This positions CDNs as critical infrastructure for web technology evolution, though the specific features and optimizations available depend significantly on the CDN provider and their technology adoption timeline.
Caveats and disclaimers
Our 2025 analysis builds upon the methodology established in previous years while incorporating new metrics and deeper performance analysis. The statistics gathered focus on applicable technologies and optimization patterns rather than vendor-specific performance comparisons.
Important note on measurements: All TLS negotiation times, DNS resolution times, and performance metrics in this analysis are measured from HTTP Archive’s simulated browser connections using Chrome on controlled infrastructure. These measurements represent:
- Consistent network conditions (controlled datacenter connectivity)
- Chrome browser’s TLS implementation
- First-time connections without session resumption
- Standardized measurement methodology across all CDNs
Real-world performance may vary based on geographic proximity to CDN edge servers, network conditions, TLS session resumption capabilities, and client device characteristics.
Key limitations of our testing methodology:
- Simulated network conditions: Tests use controlled network environments
- Single geographic perspective: Analysis from limited datacenter locations
- Cache effectiveness: Each CDN uses proprietary technology and many, for security reasons, do not expose cache performance or depth of cache
- Localization and internationalization: Just like geographic distribution, the effects of language and geographic specific domains are also opaque to these tests
- CDN detection: This is primarily done through DNS resolution and HTTP headers. Most CDNs use a DNS CNAME to map a user to an optimal data center. However, some CDNs use Anycast IPs or direct A+AAAA responses from a delegated domain which hide the DNS chain. In other cases, websites use multiple CDNs to balance between vendors, which is hidden from the single-request pass of our crawler
- Sampling bias: HTTP Archive data reflects popular websites, potentially overrepresenting certain CDN providers
- Market share interpretation: Our data shows CDN usage patterns among crawled sites, not true market distribution
CDN adoption
A web page is composed of the following key components:
- Base HTML page (for example,
www.example.com/index.html—often available at a more friendly name like justwww.example.com). - Embedded first-party content such as images, CSS, fonts and JavaScript files on the main domain (
www.example.com) and the subdomains (for example,images.example.com, orassets.example.com). - Third-party content (for example, Google Analytics, advertisements) served from third-party domains.
The evolution of CDN adoption patterns reflects the changing nature of web architecture and the increasing complexity of modern web applications. CDNs continue to prove their value across different content types, with varying adoption rates that reflect their suitability for different use cases.
The chart shows the breakdown of requests for different types of content (HTML, Subdomain, and Third-party), showing the share of content served by CDN versus origin on mobile devices.
CDNs are often utilized for delivering static content such as fonts, image files, stylesheets, and JavaScript. This kind of content doesn’t change frequently, making it a good candidate for caching on CDN proxy servers. We still see CDNs used more frequently for this type of resource, especially for third-party content, with 71% being served via CDN. Subdomain resources show moderate CDN adoption at 52%, while HTML content has the lowest CDN usage at 35%, as it’s more commonly served directly from origin servers.
From 2024 to 2025, we see mixed trends across content types. HTML content continued its upward trajectory, increasing from 33% to 35%. Subdomain content remained stable at 52% in both years. However, third-party content experienced a notable decline from 75% in 2024 to 71% in 2025, representing a four percentage point decrease after years of consistent growth.
The share of CDN usage has increased over the years, particularly among the most popular websites according to Google Chrome’s UX Report (CrUX) classification. As the graph shows, the top 1,000 websites have the highest CDN usage at 71%, followed by the top 10,000 at 70%, and the top 100,000 at 62%. Compared to 2024, CDN adoption has increased regardless of popularity rank.
As mentioned in previous editions, the increase in CDN usage of 33% in 2024 to 35% in 2025 among smaller sites can be attributed to the rise of free or flat-tiered or affordable CDN options. Additionally, many hosting solutions now bundle CDNs with their services, making it easier and more cost-effective for websites to leverage this technology.
CDN providers
CDN providers can generally be classified into two segments:
- Generic CDNs: Providers that offer a wide range of content delivery services to suit various use cases, including Akamai, Cloudflare, Amazon CloudFront, and Fastly.
- Purpose-built CDNs: Providers tailored to specific platforms or use cases, such as Netlify and WordPress.
Generic CDNs address broad market needs with offerings that include:
- Website delivery
- Web application API delivery
- Video streaming
- Edge Computing services
- Web security offerings
These capabilities appeal to a wide range of industries, which is reflected in the data.
The leading vendors for serving base HTML requests are Cloudflare, with a 58% share, followed by Google (21%), Amazon CloudFront (7%), Fastly (5%), and Akamai and Vercel, each with a 2% share.
Marginally changing from 2024, the leading vendors in this category are Cloudflare (46%), Amazon CloudFront (28%), Google (5%), and Akamai (4%).
Google leads the list third-party domain usage at 53% market share, followed by well-known CDN providers such as Cloudflare (17%), Amazon CloudFront (11%), Fastly (5%), and Akamai and Facebook (4%).
While many CDNs offer purpose-built features optimized specifically for content delivery, they increasingly exist as part of larger service ecosystems. These CDNs are often tightly integrated with cloud infrastructure, security solutions, and edge computing platforms, with these adjacent services delivered through or alongside the CDN itself.
Different CDN providers take distinct approaches to optimization and specialization. Third-party platforms like Google and Facebook build highly specialized CDNs engineered specifically for their needs, handling massive throughput for ad delivery and capturing analytics beacons at scale. In contrast, general-purpose CDNs like Cloudflare and Amazon CloudFront optimize targeted feature sets while maintaining broader applicability. These platforms leverage their CDN capabilities as a foundation for managed services, enabling use cases such as globally distributed API gateways or real-time JavaScript injection for client-side device fingerprinting and security inspection.
HTTP/3 adoption
Published in June 2022 by IETF, HTTP/3 is a major revision of the HTTP network protocol, succeeding HTTP/2. The transition to HTTP/3 represents one of the most significant protocol upgrades in web history. Built on QUIC transport, HTTP/3 eliminates head-of-line blocking and reduces connection establishment overhead. Our 2025 analysis reveals dramatic shifts in adoption patterns, particularly among CDN providers.
HTTP/3’s performance improvements stem from fundamental protocol design changes that CDNs are uniquely positioned to leverage at global scale. Unlike HTTP/2’s reliance on TCP, HTTP/3 uses QUIC over UDP, eliminating TCP’s head-of-line blocking. When one HTTP/2 stream encounters packet loss, all multiplexed streams on that TCP connection stall. CDNs implementing HTTP/3 can maintain performance for unaffected requests through QUIC’s independent stream recovery. This is particularly valuable for CDNs serving mixed content where a slow loading image won’t block critical CSS or JavaScript delivery.
HTTP/3 reduces connection establishment from HTTP/2’s 3 RTTs (TCP handshake, TLS handshake, and HTTP negotiation) to 1 RTT through QUIC’s integrated cryptographic handshake. CDNs amplify this benefit through geographic proximity, as users connecting to nearby CDN edge servers experience reduced connection time. For returning visitors, some CDNs implement 0-RTT connection resumption, eliminating handshake overhead entirely when reconnecting to the same edge server.
Modern CDNs are beginning to implement HTTPS DNS records, a type of Service Binding (SVCB) / HTTPS records that allows DNS responses to advertise HTTP/3 availability and connection parameters directly. When a browser queries DNS for a CDN enabled domain, HTTPS records can indicate HTTP/3 support on port 443 with specific QUIC parameters, enabling immediate HTTP/3 connections without the traditional HTTP/2 to HTTP/3 upgrade process. This DNS level optimization is particularly powerful for CDNs managing multiple domains and services, as it eliminates protocol upgrade negotiations and can reduce connection establishment time. However, HTTPS record implementation varies significantly across CDN providers, with some leading adoption while others have not yet implemented support.
Important methodological considerations
Our HTTP/3 adoption measurements reflect the specific characteristics of HTTP Archive’s methodology and should not be interpreted as representative of overall internet traffic:
- Site Selection: Analysis focuses on popular websites (top 10M) that are more likely to implement modern protocols
- Resource Type Focus: Measurements primarily reflect static resources (CSS, JS, images) served by CDNs rather than main document loads
- Geographic Scope: Testing from limited datacenter locations may not reflect global user experience
- External Validation: Cloudflare’s own 2025 data reports ~21% HTTP/3 adoption globally, significantly lower than the 69% we observe for Cloudflare resources in our dataset
These measurements are valuable for understanding protocol adoption among leading web properties and CDN-served resources, but should not be extrapolated to represent general internet usage patterns.
HTTP/3 adoption among CDN providers
In 2025, using consistent methodology from previous years, we observed significant HTTP/3 adoption among CDN-served resources. While these numbers reflect the specific subset of sites and resources in our dataset, they demonstrate clear patterns in CDN protocol deployment:
Within our dataset, the data reinforces the role CDNs play in driving the adoption of new protocols among popular websites and static resources. CDNs saw 29% traffic from HTTP/3 with effectively 0% for origin traffic. Compared to 2024, we observed a sharp decrease in CDN usage for HTTP/1.1 in 2025.
While HTTP/1.1 usage has been on a continued decline with CDNs over the past several years, in 2025 we observed a sharp decrease in CDN usage for HTTP/1.1 going from 16% usage for HTML requests in 2024 to just 2% in 2025. This decrease was even more pronounced for origin requests with 56% HTTP/1.1 requests in 2024 down to 21% in 2025.
Looking at individual CDNs HTTP/3 support we see the following for documents (often the initial requests):
| CDN | Desktop | Mobile |
|---|---|---|
| Cloudflare | 44.0% | 49.9% |
| CDN | 6.2% | 5.0% |
| Amazon CloudFront | 3.2% | 3.8% |
| Sucuri Firewall | 0.5% | 0.6% |
| Akamai | 0.2% | 0.2% |
| QUIC.cloud | 0.1% | 0.1% |
| 0.1% | 0.1% |
Special call out to Cloudflare who are leading the industry here.
While subresources requests have a much higher rate of adoption since they often are used for multiple requests where subsequent requests are more likely to be made over HTTP/3:
| CDN | Desktop | Mobile |
|---|---|---|
| 99.4% | 99.9% | |
| Nexcess CDN | 97.7% | 99.6% |
| Sucuri Firewall | 71.2% | 68.4% |
| Cloudflare | 68.6% | 69.5% |
| Reapleaf | 59.5% | 59.1% |
| Erstream | 31.5% | 77.4% |
| QUIC.cloud | 48.8% | 47.3% |
| 39.6% | 42.2% | |
| Pressable CDN | 40.1% | 40.8% |
| Automattic | 25.6% | 29.0% |
CDN Performance
CDN performance extends beyond simply caching content closer to users. CDNs actively optimize the underlying protocols and connection mechanisms that determine how quickly browsers can establish connections and receive data while providing transparent metrics to understand bottlenecks in modern web applications. Performance optimization techniques include connection pooling, protocol translation, and intelligent routing—all of which contribute to reduced latency and improved user experience.
HTTP/3 TTFB Performance
Below shows the time to first byte (TTFB) median percentile distribution for latency of HTTP/3, HTTP/2, and HTTP/1.1 across major CDNs. These measurements reflect simulated browser connections and may vary from real-world performance.
