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1Technology

2Security and privacy

3Content networking techniques

Toggle Content networking techniques subsection

3.1Content service protocols

3.2Peer-to-peer CDNs

3.3Private CDNs

4CDN trends

Toggle CDN trends subsection

4.1Emergence of telco CDNs

4.2Telco CDN advantages

4.3Federated CDNs and Open Caching

4.4Improving CDN performance using Extension Mechanisms for DNS

4.5Virtual CDN (vCDN)

4.6Image Optimization and Delivery (Image CDNs)

5Notable content delivery service providers

Toggle Notable content delivery service providers subsection

5.1Free CDNs

5.2Traditional commercial CDNs

5.3Telco CDNs

5.4Commercial CDNs using P2P for delivery

5.5Multi CDN

5.6In-house CDN

6See also

7References

8Further reading

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Content delivery network

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From Wikipedia, the free encyclopedia

Layer in the internet ecosystem addressing bottlenecks

(Left) Single server distribution (Right) CDN scheme of distribution

A content delivery network or content distribution network (CDN) is a geographically distributed network of proxy servers and their data centers. The goal is to provide high availability and performance by distributing the service spatially relative to end users. CDNs came into existence in the late 1990s as a means for alleviating the performance bottlenecks of the Internet[1][2] as the Internet was starting to become a mission-critical medium for people and enterprises. Since then, CDNs have grown to serve a large portion of the Internet content today, including web objects (text, graphics and scripts), downloadable objects (media files, software, documents), applications (e-commerce, portals), live streaming media, on-demand streaming media, and social media sites.[3]

CDNs are a layer in the internet ecosystem. Content owners such as media companies and e-commerce vendors pay CDN operators to deliver their content to their end users. In turn, a CDN pays Internet service providers (ISPs), carriers, and network operators for hosting its servers in their data centers.

CDN is an umbrella term spanning different types of content delivery services: video streaming, software downloads, web and mobile content acceleration, licensed/managed CDN, transparent caching, and services to measure CDN performance, load balancing, Multi CDN switching and analytics and cloud intelligence. CDN vendors may cross over into other industries like security, DDoS protection and web application firewalls (WAF), and WAN optimization.

Technology[edit]

CDN nodes are usually deployed in multiple locations, often over multiple Internet backbones. Benefits include reducing bandwidth costs, improving page load times, and increasing the global availability of content. The number of nodes and servers making up a CDN varies, depending on the architecture, some reaching thousands of nodes with tens of thousands of servers on many remote points of presence (PoPs). Others build a global network and have a small number of geographical PoPs.[4]

Requests for content are typically algorithmically directed to nodes that are optimal in some way. When optimizing for performance, locations that are best for serving content to the user may be chosen. This may be measured by choosing locations that are the fewest hops, the lowest number of network seconds away from the requesting client, or the highest availability in terms of server performance (both current and historical), to optimize delivery across local networks. When optimizing for cost, locations that are the least expensive may be chosen instead. In an optimal scenario, these two goals tend to align, as edge servers that are close to the end user at the edge of the network may have an advantage in performance or cost.

Most CDN providers will provide their services over a varying, defined, set of PoPs, depending on the coverage desired, such as United States, International or Global, Asia-Pacific, etc. These sets of PoPs can be called "edges", "edge nodes", "edge servers", or "edge networks" as they would be the closest edge of CDN assets to the end user.[5]

Security and privacy[edit]

CDN providers profit either from direct fees paid by content providers using their network, or profit from the user analytics and tracking data collected as their scripts are being loaded onto customers' websites inside their browser origin. As such these services are being pointed out as potential privacy intrusions for the purpose of behavioral targeting[6] and solutions are being created to restore single-origin serving and caching of resources.[7]

In particular, a website using a CDN may violate the EU's General Data Protection Regulation (GDPR). For example, in 2021 a German court forbade the use of a CDN on a university website, because this caused the transmission of the user's IP address to the CDN, which violated the GDPR.[8]

CDNs serving JavaScript have also been targeted as a way to inject malicious content into pages using them. Subresource Integrity mechanism was created in response to ensure that the page loads a script whose content is known and constrained to a hash referenced by the website author.[9]

Content networking techniques[edit]

The Internet was designed according to the end-to-end principle.[10]

This principle keeps the core network relatively simple and moves the intelligence as much as possible to the network end-points: the hosts and clients. As a result, the core network is specialized, simplified, and optimized to only forward data packets.

Content Delivery Networks augment the end-to-end transport network by distributing on it a variety of intelligent applications employing techniques designed to optimize content delivery. The resulting tightly integrated overlay uses web caching, server-load balancing, request routing, and content services.[11]

Web caches store popular content on servers that have the greatest demand for the content requested. These shared network appliances reduce bandwidth requirements, reduce server load, and improve the client response times for content stored in the cache. Web caches are populated based on requests from users (pull caching) or based on preloaded content disseminated from content servers (push caching).[12]

Server-load balancing uses one or more techniques including service-based (global load balancing) or hardware-based (i.e. layer 4–7 switches, also known as a web switch, content switch, or multilayer switch) to share traffic among a number of servers or web caches. Here the switch is assigned a single virtual IP address. Traffic arriving at the switch is then directed to one of the real web servers attached to the switch. This has the advantage of balancing load, increasing total capacity, improving scalability, and providing increased reliability by redistributing the load of a failed web server and providing server health checks.

A content cluster or service node can be formed using a layer 4–7 switch to balance load across a number of servers or a number of web caches within the network.

Request routing directs client requests to the content source best able to serve the request. This may involve directing a client request to the service node that is closest to the client, or to the one with the most capacity. A variety of algorithms are used to route the request. These include Global Server Load Balancing, DNS-based request routing, Dynamic metafile generation, HTML rewriting,[13] and anycasting.[14] Proximity—choosing the closest service node—is estimated using a variety of techniques including reactive probing, proactive probing, and connection monitoring.[11]

CDNs use a variety of methods of content delivery including, but not limited to, manual asset copying, active web caches, and global hardware load balancers.

Content service protocols[edit]

Several protocol suites are designed to provide access to a wide variety of content services distributed throughout a content network. The Internet Content Adaptation Protocol (ICAP) was developed in the late 1990s[15][16] to provide an open standard for connecting application servers. A more recently defined and robust solution is provided by the Open Pluggable Edge Services (OPES) protocol.[17] This architecture defines OPES service applications that can reside on the OPES processor itself or be executed remotely on a Callout Server. Edge Side Includes or ESI is a small markup language for edge-level dynamic web content assembly. It is fairly common for websites to have generated content. It could be because of changing content like catalogs or forums, or because of the personalization. This creates a problem for caching systems. To overcome this problem, a group of companies created ESI.

Peer-to-peer CDNs[edit]

Further information: Peer-to-peer network

In peer-to-peer (P2P) content-delivery networks, clients provide resources as well as use them. This means that, unlike client–server systems, the content-centric networks can actually perform better as more users begin to access the content (especially with protocols such as Bittorrent that require users to share). This property is one of the major advantages of using P2P networks because it makes the setup and running costs very small for the original content distributor.[18][19]

Private CDNs[edit]

If content owners are not satisfied with the options or costs of a commercial CDN service, they can create their own CDN. This is called a private CDN. A private CDN consists of PoPs (points of presence) that are only serving content for their owner. These PoPs can be caching servers,[20] reverse proxies or application delivery controllers.[21] It can be as simple as two caching servers,[20] or large enough to serve petabytes of content.[22]

Large content distribution networks may even build and set up their own private network to distribute copies of content across cache locations.[23][24] Such private networks are usually used in conjunction with public networks as a backup option in case the capacity of the private network is not enough or there is a failure which leads to capacity reduction. Since the same content has to be distributed across many locations, a variety of multicasting techniques may be used to reduce bandwidth consumption. Over private networks, it has also been proposed to select multicast trees according to network load conditions to more efficiently utilize available network capacity.[25][26]

CDN trends[edit]

Emergence of telco CDNs[edit]

The rapid growth of streaming video traffic[27] uses large capital expenditures by broadband providers[28] in order to meet this demand and retain subscribers by delivering a sufficiently good quality of experience.

To address this, telecommunications service providers have begun to launch their own content delivery networks as a means to lessen the demands on the network backbone and reduce infrastructure investments.

Telco CDN advantages[edit]

Because they own the networks over which video content is transmitted, telco CDNs have advantages over traditional CDNs. They own the last mile and can deliver content closer to the end-user because it can be cached deep in their networks. This deep caching minimizes the distance that video data travels over the general Internet and delivers it more quickly and reliably.

Telco CDNs also have a built-in cost advantage since traditional CDNs must lease bandwidth from them and build the operator's margin into their own cost model. In addition, by operating their own content delivery infrastructure, telco operators have better control over the utilization of their resources. Content management operations performed by CDNs are usually applied without (or with very limited) information about the network (e.g., topology, utilization etc.) of the telco-operators with which they interact or have business relationships. These pose a number of challenges for the telco-operators who have a limited sphere of action in face of the impact of these operations on the utilization of their resources.

In contrast, the deployment of telco-CDNs allows operators to implement their own content management operations,[29][30] which enables them to have a better control over the utilization of their resources and, as such, provide better quality of service and experience to their end users.

Federated CDNs and Open Caching[edit]

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources in this section. Unsourced material may be challenged and removed. (June 2021) (Learn how and when to remove this template message)

In June 2011, StreamingMedia.com reported that a group of TSPs had founded an Operator Carrier Exchange (OCX)[31] to interconnect their networks and compete more directly against large traditional CDNs like Akamai and Limelight Networks, which have extensive PoPs worldwide. This way, telcos are building a Federated CDN offering, which is more interesting for a content provider willing to deliver its content to the aggregated audience of this federation.

It is likely that in a near future, other telco CDN federations will be created. They will grow by enrollment of new telcos joining the federation and bringing network presence and their Internet subscriber bases to the existing ones.[citation needed]

The Open Caching specification by Streaming Media Alliance defines a set of APIs that allows a Content Provider to deliver its content using several CDNs in a consistent way, seeing each CDN provider the same way through these APIs.

Improving CDN performance using Extension Mechanisms for DNS[edit]

The latency (RTT) experienced by clients with non-local resolvers ("high") reduced drastically when a CDN rolled-out the EDNS0 extension in April 2014, while the latency of clients with local resolvers are unimpacted by the change ("low").[32]

Traditionally, CDNs have used the IP of the client's recursive DNS resolver to geo-locate the client. While this is a sound approach in many situations, this leads to poor client performance if the client uses a non-local recursive DNS resolver that is far away. For instance, a CDN may route requests from a client in India to its edge server in Singapore, if that client uses a public DNS resolver in Singapore, causing poor performance for that client. Indeed, a recent study[32] showed that in many countries where public DNS resolvers are in popular use, the median distance between the clients and their recursive DNS resolvers can be as high as a thousand miles. In August 2011, a global consortium of leading Internet service providers led by Google announced their official implementation of the edns-client-subnet IETF Internet Draft,[33] which is intended to accurately localize DNS resolution responses. The initiative involves a limited number of leading DNS service providers, such as Google Public DNS,[34] and CDN service providers as well. With the edns-client-subnet EDNS0 option, CDNs can now utilize the IP address of the requesting client's subnet when resolving DNS requests. This approach, called end-user mapping,[32] has been adopted by CDNs and it has been shown to drastically reduce the round-trip latencies and improve performance for clients who use public DNS or other non-local resolvers. However, the use of EDNS0 also has drawbacks as it decreases the effectiveness of caching resolutions at the recursive resolvers,[32] increases the total DNS resolution traffic,[32] and raises a privacy concern of exposing the client's subnet.

Virtual CDN (vCDN)[edit]

Virtualization technologies are being used to deploy virtual CDNs (vCDNs) with the goal to reduce content provider costs, and at the same time, increase elasticity and decrease service delay. With vCDNs, it is possible to avoid traditional CDN limitations, such as performance, reliability and availability since virtual caches are deployed dynamically (as virtual machines or containers) in physical servers distributed across the provider's geographical coverage. As the virtual cache placement is based on both the content type and server or end-user geographic location, the vCDNs have a significant impact on service delivery and network congestion.[35][36][37][38]

Image Optimization and Delivery (Image CDNs)[edit]

In 2017, Addy Osmany of Google started referring to software solutions that could integrate naturally with the Responsive Web Design paradigm (with particular reference to the element) as Image CDNs.[39] The expression referred to the ability of a web architecture to serve multiple versions of the same image through HTTP, depending on the properties of the browser requesting it, as determined by either the browser or the server-side logic. The purpose of Image CDNs was, in Google's vision, to serve high-quality images (or, better, images perceived as high-quality by the human eye) while preserving download speed, thus contributing to a great User experience (UX).[citation needed]

Arguably, the Image CDN term was originally a misnomer, as neither Cloudinary nor Imgix (the examples quoted by Google in the 2017 guide by Addy Osmany) were, at the time, a CDN in the classical sense of the term.[39] Shortly afterwards, though, several companies offered solutions that allowed developers to serve different versions of their graphical assets according to several strategies. Many of these solutions were built on top of traditional CDNs, such as Akamai, CloudFront, Fastly, Edgecast and Cloudflare. At the same time, other solutions that already provided an image multi-serving service joined the Image CDN definition by either offering CDN functionality natively (ImageEngine)[40] or integrating with one of the existing CDNs (Cloudinary/Akamai, Imgix/Fastly).

While providing a universally agreed-on definition of what an Image CDN is may not be possible, generally speaking, an Image CDN supports the following three components:[41]

A Content Delivery Network (CDN) for the fast serving of images.

Image manipulation and optimization, either on-the-fly through URL directives, in batch mode (through manual upload of images) or fully automatic (or a combination of these).

Device Detection (also known as Device Intelligence), i.e. the ability to determine the properties of the requesting browser and/or device through analysis of the User-Agent string, HTTP Accept headers, Client-Hints or JavaScript.[41]

The following table summarizes the current situation with the main software CDNs in this space:[42]

Main Image CDNs on the market

Name

CDN

Image Optimization

Device Detection

Akamai ImageManager

Batch mode

based on HTTP Accept header

Cloudflare Polish

fully-automatic

based on HTTP Accept header

Cloudinary

Through Akamai

Batch, URL directives

Accept header, Client-Hints

Fastly IO

URL directives

based on HTTP Accept header

ImageEngine

fully-automatic

WURFL, Client-Hints, Accept header

Imgix

Through Fastly

fully-automatic

Accept header / Client-Hints

PageCDN

URL directives

based on HTTP Accept header

Notable content delivery service providers[edit]

Free CDNs[edit]

cdnjs[43][44]

BootstrapCDN

Cloudflare

JSDelivr

Traditional commercial CDNs[edit]

Akamai Technologies[45]

Amazon CloudFront[45]

Aryaka

Ateme CDN

Azure CDN

bunny.net

CacheFly

CDN77[46]

CDNetworks[45]

CenterServ[45]

ChinaCache

Cloudflare[47]

Cotendo

Edgio, formed through merger of EdgeCast Networks, Layer0 and Limelight Networks

Fastly

Gcore

Google Cloud CDN

HP Cloud Services

Incapsula

Instart

Internap

LeaseWeb

Lumen Technologies, formerly Level 3 Communications

MetaCDN

NACEVI

OnApp

GoDaddy

OVHcloud

Rackspace Cloud Files

Speedera Networks

StackPath

StreamZilla

Wangsu Science & Technology

Yottaa

Telco CDNs[edit]

AT&T Inc.

Bharti Airtel

Bell Canada

BT Group

China Telecom

Chunghwa Telecom

Deutsche Telekom

KPN

Lumen Technologies, formerly CenturyLink

Megafon

NTT

Pacnet

PCCW

Singtel

SK Broadband

Spark New Zealand[citation needed]

Tata Communications

Telecom Argentina

Telefonica

Telenor

TeliaSonera

Telin

Telstra

Telus

TIM

Türk Telekom

Verizon

Commercial CDNs using P2P for delivery[edit]

BitTorrent, Inc.

Internap

Pando Networks

Rawflow

Multi CDN[edit]

MetaCDN

Warpcache[48][49]

In-house CDN[edit]

Netflix[50]

What is a CDN? - Content Delivery Network Explained - AWS

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What is a CDN?

Why is a CDN important?

What are the benefits of CDNs?

What is the history of CDN technology?

What internet content can a CDN deliver?

How does a CDN work?

What is a CDN used for?

What is Amazon CloudFront?

What is a CDN?

A content delivery network (CDN) is a network of interconnected servers that speeds up webpage loading for data-heavy applications. CDN can stand for content delivery network or content distribution network. When a user visits a website, data from that website's server has to travel across the internet to reach the user's computer. If the user is located far from that server, it will take a long time to load a large file, such as a video or website image. Instead, the website content is stored on CDN servers geographically closer to the users and reaches their computers much faster.

Why is a CDN important?

The primary purpose of a content delivery network (CDN) is to reduce latency, or reduce the delay in communication created by a network's design. Because of the global and complex nature of the internet, communication traffic between websites (servers) and their users (clients) has to move over large physical distances. The communication is also two-way, with requests going from the client to the server and responses coming back. A CDN improves efficiency by introducing intermediary servers between the client and the website server. These CDN servers manage some of the client-server communications. They decrease web traffic to the web server, reduce bandwidth consumption, and improve the user experience of your applications.

What are the benefits of CDNs?

Content delivery networks (CDNs) provide many benefits that improve website performance and support core network infrastructure. For example, a CDN can do the following tasks:

Reduce page load time

Website traffic can decrease if your page load times are too slow. A CDN can reduce bounce rates and increase the time users spend on your site.

Reduce bandwidth costs

Bandwidth costs are a significant expense because every incoming website request consumes network bandwidth. Through caching and other optimizations, CDNs can reduce the amount of data an origin server must provide, reducing the costs of hosting for website owners.

Increase content availability

Too many visitors at one time or network hardware failures can cause a website to crash. CDN services can handle more web traffic and reduce the load on web servers. Also, if one or more CDN servers go offline, other operational servers can replace them to ensure uninterrupted service.

Improve website security

Distributed denial-of-service (DDoS) attacks attempt to take down applications by sending large amounts of fake traffic to the website. CDNs can handle such traffic spikes by distributing the load between several intermediary servers, reducing the impact on the origin server.

What is the history of CDN technology?

Content delivery network (CDN) technology emerged in the late 1990s with the focus on faster content delivery over the internet:

First generation

First-generation CDN services focused on networking principles of intelligent network traffic management and data centers for replication.

Second generation

Second-generation CDNs arose in response to the rise of audio and video streaming services, especially video on demand and news on demand. The technology also evolved to solve new challenges in content delivery on mobile devices. Companies used cloud computing techniques and peer-to-peer networks to accelerate content delivery.

Third generation

Third-generation CDNs are still evolving. AWS is driving innovation as one of the leading CDN service providers in the world. With most web services centralized in the cloud, the focus is now on edge computing—managing bandwidth consumption using smart devices that communicate intelligently. Autonomous and self-managed edge networks might be the next step in CDN technology.

What internet content can a CDN deliver?

A content delivery network (CDN) can deliver two types of content: static content and dynamic content.

Static content

Static content is website data that does not change from user to user. Website header images, logos, and font styles remain the same across all users, and the business does not change them frequently. Static data does not need to be modified, processed, or generated and is ideal for storage on a CDN.

Dynamic content

Dynamic content such as social media news feeds, weather reports, login status, and chat messages vary among website users. This data changes based on the user's location, login time, or user preferences, and the website must generate the data for every user and every user interaction.

How does a CDN work?

Content delivery networks (CDNs) work by establishing a point of presence (POP) or a group of CDN edge servers at multiple geographical locations. This geographically distributed network works on the principles of caching, dynamic acceleration, and edge logic computations.

Caching

Caching is the process of storing multiple copies of the same data for faster data access. In computing, the principle of caching applies to all types of memory and storage management. In CDN technology, the term refers to the process of storing static website content on multiple servers in the network. Caching in CDN works as follows:

A geographically remote website visitor makes the first request for static web content from your site.

The request reaches your web application server or origin server. The origin server sends the response to the remote visitor. At the same time, it also sends a copy of the response to the CDN POP geographically closest to that visitor.

The CDN POP server stores the copy as a cached file.

The next time this visitor, or any other visitor in that location, makes the same request, the caching server, not the origin server, sends the response.

Dynamic acceleration

Dynamic acceleration is the reduction in server response time for dynamic web content requests because of an intermediary CDN server between the web applications and the client. Caching doesn't work well with dynamic web content because the content can change with every user request. CDN servers have to reconnect with the origin server for every dynamic request, but they accelerate the process by optimizing the connection between themselves and the origin servers.

If the client sends a dynamic request directly to the web server over the internet, the request might get lost or delayed due to network latency. Time might also be spent opening and closing the connection for security verification. On the other hand, if the nearby CDN server forwards the request to the origin server, they would already have an ongoing, trusted connection established. For example, the following features could further optimize the connection between them:

Intelligent routing algorithms

Geographic proximity to the origin

The ability to process the client request, which reduces its size

Edge logic computations

You can program the CDN edge server to perform logical computations that simplify communication between the client and server. For example, this server can do the following:

Inspect user requests and modify caching behavior.

Validate and handle incorrect user requests.

Modify or optimize content before responding.

Distribution of application logic between the web servers and the network edge helps developers offload origin servers' compute requirements and improve website performance.

What is a CDN used for?

A content delivery network (CDN) improves normal website functions and increases customer satisfaction. The following are some example use cases.

High-speed content delivery

By combining static and dynamic internet content delivery, you can use CDNs to provide your customers with a global, high-performing, whole-site experience. For example, Reuters is the world's largest news wholesaler to top channels such as BBC, CNN, the New York Times, and the Washington Post. The news media challenge for Reuters is to deliver news content promptly to customers around the globe. Reuters uses Amazon's CDN service, Amazon CloudFront, with Amazon Simple Storage Service (Amazon S3) to minimize dependence on satellite link communication and create a cheaper, highly available, and secure globally distributed network platform.

Real-time streaming

CDNs help reliably and cost-effectively deliver rich and high-quality media files. Companies streaming video and audio use CDNs to overcome three challenges: reduce bandwidth costs, increase scale, and decrease delivery time. For example, Hulu is an online video streaming platform owned by the Walt Disney Company. It uses Amazon CloudFront to consistently stream more than 20 GBps of data to its growing customer base.

Multi-user scaling

CDNs help support a large number of concurrent users. Website resources can manage only a limited number of client connections at a time. CDNs can rapidly scale this number by taking some of the load from the application server. For instance, King is a gaming company that builds socially connected, cross-platform games that can be played anytime, anywhere, and from any device. King has over 350 million players at any time, and they play 10.6 billion games a day on the platform. King's game applications record users' game data on central data centers, allowing them to play on different devices without losing progress. The data centers aim to give users a consistent experience, even if users join the game on old machines with limited bandwidth. King uses Amazon CloudFront to deliver hundreds of terabytes of content daily, with spikes to half a petabyte or more when it launches a new game or initiates a large-scale marketing program.

What is Amazon CloudFront?

Amazon CloudFront is a content delivery network (CDN) service built for high performance, security, and developer convenience. You can use Amazon CloudFront to do these tasks:

Deliver data through 450+ globally dispersed points of presence (POPs) with automated network mapping and intelligent routing.

Improve security with traffic encryption and access controls, and use AWS Shield Standard to defend against distributed denial-of-service (DDoS) attacks at no additional charge.

Customize the code you run at the AWS network edge using serverless compute features to balance cost, performance, and security.

Scale automatically to deliver software, game patches, and IoT updates with high transfer rates.

Start building on AWS CloudFront with 50 GB of free data transfer out for 12 months. Create a free AWS account today.

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What is a content delivery network on Azure?

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03/28/2023

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A content delivery network (CDN) is a distributed network of servers that can efficiently deliver web content to users. A CDN store cached content on edge servers in point-of-presence (POP) locations that are close to end users, to minimize latency.

Azure CDN offers developers a global solution for rapidly delivering high-bandwidth content to users by caching their content at strategically placed physical nodes across the world. Azure CDN can also accelerate dynamic content, which can't get cached, by using various network optimizations using CDN POPs. For example, route optimization to bypass Border Gateway Protocol (BGP).

The benefits of using Azure CDN to deliver web site assets include:

Better performance and improved user experience for end users, especially when using applications where multiple round-trips requests required by end users to load contents.

Large scaling to better handle instantaneous high loads, such as the start of a product launch event.

Distribution of user requests and serving of content directly from edge servers so that less traffic gets sent to the origin server.

For a list of current CDN node locations, see Azure CDN POP locations.

How it works

A user (Alice) requests a file (also called an asset) by using a URL with a special domain name, such as .azureedge.net. This name can be an endpoint hostname or a custom domain. The DNS routes the request to the best performing POP location, which is usually the POP that is geographically closest to the user.

If no edge servers in the POP have the file in their cache, the POP requests the file from the origin server. The origin server can be an Azure Web App, Azure Cloud Service, Azure Storage account, or any publicly accessible web server.

The origin server returns the file to an edge server in the POP.

An edge server in the POP caches the file and returns the file to the original requestor (Alice). The file remains cached on the edge server in the POP until the time-to-live (TTL) specified by its HTTP headers expires. If the origin server didn't specify a TTL, the default TTL is seven days.

More users can then request the same file by using the same URL that Alice used, and gets directed to the same POP.

If the TTL for the file hasn't expired, the POP edge server returns the file directly from the cache. This process results in a faster, more responsive user experience.

Requirements

To use Azure CDN, you must own at least one Azure subscription.

You also need to create a CDN profile, which is a collection of CDN endpoints. Every CDN endpoint is a specific configuration which users can customize with required content delivery behavior and access. To organize your CDN endpoints by internet domain, web application, or some other criteria, you can use multiple profiles.

Since Azure CDN pricing gets applied at the CDN profile level, so if you want to use a mix of pricing tiers you must create multiple CDN profiles. For information about the Azure CDN billing structure, see Understanding Azure CDN billing.

Limitations

Each Azure subscription has default limits for the following resources:

The number of CDN profiles created.

The number of endpoints created in a CDN profile.

The number of custom domains mapped to an endpoint.

For more information about CDN subscription limits, see CDN limits.

Azure CDN features

Azure CDN offers the following key features:

Dynamic site acceleration

CDN caching rules

HTTPS custom domain support

Azure diagnostics logs

File compression

Geo-filtering

For a complete list of features that each Azure CDN product supports, see Compare Azure CDN product features.

Next steps

To get started with CDN, see Create an Azure CDN profile and endpoint.

Manage your CDN endpoints through the Microsoft Azure portal or with PowerShell.

Learn how to automate Azure CDN with .NET or Node.js.

Learn module: Introduction to Azure Content Delivery Network (CDN).

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What is a CDN (Content Delivery Network)? | DigitalOcean

is a CDN (Content Delivery Network)? | DigitalOceanBlogDocsGet SupportContact SalesProductsFeatured ProductsDropletsScalable virtual machinesKubernetesManaged Kubernetes clustersPaperspaceBuild & scale AI modelsCloudwaysManaged cloud hostingApp PlatformGet apps to market fasterDatabasesWorry-free setup & maintenanceComputeDropletsCPU-Optimized DropletsKubernetesApp PlatformFunctionsGPUsBackups & SnapshotsBackupsSnapshotsSnapShooterCloudways AutonomousStorageSpaces Object StorageVolumes Block StorageNetworkingVirtual Private Cloud (VPC)Cloud FirewallsLoad BalancersDNSDDoS ProtectionManaged DatabasesMongoDBKafkaMySQLPostgreSQLManaged Databases for Redis®Developer ToolsAPICLISupport PlansMonitoringUptimeAI/MLPaperspaceCloud Website HostingCloudwaysSee all productsSee what's new at DigitalOceanSolutionsCloudwaysManaged WordPressMake your website faster and more secure.Managed WoocommerceHassle-free ecommerce website hosting.Managed MagentoSimple, efficient ecommerce hosting.By industryData AnalyticsDigital Marketing AgenciesEcommerceAdvertising and Marketing TechISVs build, scale and growIT ConsultingDeveloper ToolsCI/CD PipelinesView All IndustriesBy use caseCloud VPNWeb & Mobile AppsGame DevelopmentVideo StreamingVirtual MachinesBlockchainWebsite HostingVPS HostingView All Use CasesQuestions?Speak With an ExpertSee all solutionsDevelopersOur communityDeveloper CenterLearn, build, and scale.Community HomeDevOps and development guides.CSS-TricksAll things web design.ResourcesTutorialsQuestions And AnswersMarketplaceToolsWrite for DOnationsCustomer StoriesDigitalOcean BlogGet InvolvedHatch Startup ProgramOpen Source SponsorshipsHacktoberfestDO ImpactNonprofitsDocumentationQuick StartDropletsStorageApp PlatformAPI ReferenceDomains and DNSBusinessesGrow your businessThe WaveContent to level up your business.Find a partnerWork with a partner to get up and running in the cloud.Become a partnerJoin our Partner Pod to connect with SMBs and startups like yoursUGURUSElite training for agencies & freelancers.ResourcesCustomer StoriesHatch Startup ProgramPrice Estimate CalculatorOne-Click AppsSecurityMigrate Workloads to DigitalOceanFeatured articlesCloud cost optimization best practicesRead moreHow to choose a cloud providerRead moreUnderstanding cash flow vs. profitRead moreContactDo you have any questions?Contact salesPricingLog inSign upBlogDocsGet SupportSalesCloud educationWhat is a CDN (Content Delivery Network)? Roxana ElliottPosted: January 18, 2022•8 min readCONTENTSBenefits of CDNsHow do CDNs work?How CDNs cache contentHow CDNs improve website securityHow to choose a CDNConclusionA CDN or Content Delivery Network is a global network of servers that serves web content to end-users more quickly by storing copies of files such as images in locations that are geographically closer to the users requesting that content. By using a CDN, websites reduce the load on their origin servers, which can enable them to serve more users without fear of overloading their servers. CDNs improve user experience by contributing to faster website load times, and also improve the security of websites by enabling them to mitigate the impacts of distributed denial of service (DDoS) attacks, and by giving them the ability to install additional security proxies through the content delivery network.

Benefits of CDNs

Some of the benefits of using a Content Delivery Network include:

Decrease webpage and application load time: By caching copies of static files and delivering them from servers that are closer in distance to end-users, website load times are reduced. This improves user experience and has other benefits, such as increasing search engine optimization, as search engines take website performance into account when ranking pages.

Protect against DDoS and other attacks: CDNs protect a website’s origin server from DDoS attacks and other threats by enabling sites to handle increased traffic. Additionally, other security tools such as firewalls can be installed on the CDN and sit between a malicious user and a website.

Improve scalability: Content Delivery Networks allow websites and applications to scale up quickly, as CDNs can handle traffic spikes without websites needing to increase their origin server capacity significantly.

Reduced bandwidth and hosting costs: As CDNs cache certain web content, they reduce the amount of bandwidth needed at the origin or host server. Bandwidth expenses vary based on the hosting provider, but can be costly and unpredictable, so utilizing a CDN can save on hosting costs.

Minimizes website downtime: Having high uptime is critical for businesses that rely on their website or application to generate revenue, such as Software as a Service applications and eCommerce sites. CDNs protect against downtime through the security measures mentioned above, and can even sometimes deliver a cached version of the site if the origin server is down.

There are a few different types of CDN in operation today, including CDNs operated by telecommunication companies and private CDNs, which are purpose-built for one company. Netflix and Facebook are examples of companies that have built their own Content Delivery Networks due to their large global presence and the huge amount of content they deliver each day. However, most businesses and individuals today looking for a CDN will use a commercial Content Delivery Network, such as Akamai, Cloudflare, or Fastly. While each CDN provider has some unique features, all CDNs work using the same basic principles.

How do CDNs work?

At the heart of Content Delivery Networks, also sometimes referred to as edge networks, is a set of Points of Presence or PoPs, which are groups of servers in multiple locations around the world. The servers hosted in each PoP are known as edge servers, as they are unique to the origin server which hosts the full version of a website or software, and are located at the “edge” of a network closest to the end-user. CDNs vary in the number of PoPs they include, with some networks having thousands of PoPs in all continents, and others focusing their PoPs in key areas they serve.

Edge servers serve multiple purposes, including hosting cached files to improve performance and protecting the origin server by directing traffic to the CDN instead of directly to the origin. CDNs can host a variety of software tools that help with performance and security as edge servers act as reverse proxies, which intercept web traffic and handle it through a set of rules based on the software installed on your edge server. While CDNs are most known for caching content, they can also host threat detection software, image resizing tools, and much more. Below we outline two of the most common use cases for CDNs–caching content and protecting websites from attack.

How CDNs cache content

Each edge server hosts cached copies of web content, most often static files such as images or text files. When a user visits a website or accesses a piece of software, the Content Delivery Network will automatically route them to the closest PoP and deliver cached content from that PoP, rather than directing them to the origin server which may be further away. This step increases website speed and reduces the number of requests that go to the origin server, allowing the origin server to focus on serving more dynamic content which may be difficult to cache.

This type of caching is called server-side caching, and can also be set up without the use of a Content Delivery Network through programs such as Varnish Cache which sit in front of the origin server. However, by using server-side caching in conjunction with a CDN, websites can deliver even more optimal performance. The other commonly known caching method is client-side or browser-caching, in which copies of files are stored in a user’s local browser. Browser-caching means that if a visitor repeatedly visits a webpage, certain objects on that page, such as logo files, will be stored in their browser cache and so are delivered even more quickly. Most websites use a combination of browser-caching and server-side caching, usually through a CDN, to realize the fastest website speeds possible.

To ensure the cached files served from a CDN are up-to-date, websites enter information that tells the caching mechanism when the files expire. If a CDN discovers that a file has expired, it will re-fetch that file from the origin the first time it is requested. This is known as a “cache pull,” and is beneficial as this method means the CDN only requests files when they are needed. Another caching technique is known as “cache push,” when a website proactively tells the cache to update its files. This method can be used for larger files, or when a website updates most of its content and wants to ensure the cache has the updated content.

How CDNs improve website security

In addition to improving the performance of a website, Content Delivery Networks also improve the security of websites by detecting threats, blocking malicious traffic, and protecting the origin server from attacks. By utilizing a CDN rather than sending traffic directly to an origin server, the origin server is protected from Distributed Denial of Service attacks, in which attackers attempt to take down websites by sending a huge amount of traffic to a website at once. CDNs both distribute the traffic among multiple PoPs, enabling it to withstand the additional traffic, and can include tools that go a step further in protecting from DDoS and other security threats.

Other security tools which are offered with many CDNs include firewalls and advanced threat detection software which will stop harmful traffic from getting through to the origin server. Firewalls monitor traffic and block certain traffic from entering a website based on a set of rules, such as IP address, and more advanced firewalls may examine the contents of a data packet or create smart rules to identify threats. CDNs may also include tools that mitigate the impact of harmful bots, secure APIs, and manage the TLS/SSL certificates of websites, ensuring that traffic is encrypted. All of these security tools can ensure websites stay online, threats are quickly dealt with, and there is no threat to brand reputation based on security leaks.

How to choose a CDN

There are many CDN solutions available, and every business or individual using a CDN may have different needs and priorities. When considering what Content Delivery Network to utilize, consider these factors:

CDN use case: Depending on the function that your website or application serves, you may be serving different types of content. If you are planning to cache mostly static content such as images, most CDNs will be able to fulfill your needs, but if you want to cache dynamic content or personalized assets you should ensure your CDN will be able to handle those use cases.

PoP Network: CDNs are intended primarily to deliver content to end-users more quickly, so the location of the Points of Presence is critical when determining what CDN to use. If a majority of your traffic comes from one region, ensure that the CDN you choose has a PoP or multiple PoPs in that location. If your traffic is globally distributed, choose a CDN with many PoPs around the globe.

Available features: Content Delivery Networks can include hundreds of different products for website security, performance, and scalability. These range from basic caching tools to image optimization, advanced firewalls, and more. When determining what CDN to utilize, examine the products they offer compared to your priorities - for example, if website security is your greatest concern, choose a CDN with a robust set of security tools.

User experience: While Content Delivery Networks are a commonly used tool, the user experience can vary based on the CDN. Some CDNs may have limited or complex user interfaces, while others have intuitive dashboards and APIs that can be easily managed using existing workflows. Certain CDNs may also offer fully managed services that take setup and management off of your plate.

Price: The cost and pricing model of a CDN is important to factor into your purchasing decision. While some CDNs offer free or low-cost tiers for websites with basic caching and security needs, enterprise-level solutions can cost thousands of dollars a month. Many CDNs charge based on both the tools you utilize and the traffic that runs through the CDN, so make sure to include all of the functions you will be using and estimate how much costs will go up if your traffic increases.

Support and documentation: As with other cloud solutions and software tools, the support offered by a CDN provider can range from user-generated forums, to email support, to dedicated representatives. When determining what CDN to utilize, consider if you feel comfortable troubleshooting any issues yourself, or if you’d like more frequent access to support representatives. Look at the quality of documentation and level of support provided, along with any added cost for premium support.

Compatibility: Certain CDNs may be better suited to different content management systems or software architectures. For example, some CDNs have plugins that are built to easily work with website builders. Before you choose your CDN, examine how it will work with your current application setup and the other tools you use.

Conclusion

Content Delivery Networks are valuable tools to be used alongside your cloud computing provider. CDNs can improve the performance and security of websites and applications, reduce hosting costs, and ensure your end users have a good experience. Many DigitalOcean customers use a CDN along with their DigitalOcean Droplets for an optimal website setup. DigitalOcean also includes a CDN with DigitalOcean Spaces, our object storage solution, and App Platform, our Platform as a Service solution. Sign up for a DigitalOcean account today to get started.

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