As of April 2023, there are a reported 5.18 billion internet users in the world. Having this many users creates several challenges for service providers, and the farther the servers are from the end user, the higher the latency. A Content Delivery Network (CDN) helps to solve these latency problems by reducing the distance between network edge and the server.
A CDN is a distributed network of servers and storage devices that replicates content or services (such as audio, video, and streams) on a large number of surrogate systems placed at different locations across the world.
How does a CDN work?
CDNs use several techniques for reducing latency such as caching, load balancing, scheduling, and request routing. The goal of these techniques is to push replicated content closer to the network edge where the end user/IoT edge device is.
Description: The architecture of a CDN, Wang et.al. Source.
The CDN consists of an origin or a base server that contains all kinds of data. The surrogate servers, also known as PoPs (Points of presence), are distributed around the globe at different locations to distribute load from the origin server. Content is pushed from the origin server to the PoP servers. When a user initiates a request it is routed to the nearest PoP server; if the content or data does not exist, only then the request is extended to the origin server. These servers also perform prefetching which uses data analysis to predict the kind of data that might be needed for users in a specific geographic location and fetches it from the origin server in advance.
The CDN algorithm is also programmed to consider different QoS (Quality of Service) metrics such as server load, latency, traffic volume, client access networks, and proximity. For instance, if the physically closest server is suffering from network congestion, the request could be routed to the second closest server resulting in the farther server giving a lower latency.
Benefits of using a CDN
In cloud computing services, enterprises would need to perform queries for data analysis to yield actionable business intelligence. If the data servers are located at a long distance, the data read and write processes become slow and damage business prospects. Data needs to be rapidly fetched and processed to keep up with the pace of rapidly changing online trends.
For an OTT (over-the-top) media service (such as Netflix, Amazon Prime, or HBOmax) the performance and speed of content streaming are imperative to the functioning and the ultimate success of the network. A stream that lags and has a low-quality display affects the customer base negatively.
The CDN can help with these quality-related problems and is designed to boost the performance of web applications, and pre-caching or prefetching means the predictable data already resides in servers near to the user and can be loaded at higher speeds. The distributed architecture with several POP servers also results in higher availability and responsiveness.
Additionally, CDN service providers also employ network security protocols to protect against cyber fraud, distributed denial Of service (DDoS) attacks, viruses, and other cyber attacks. This way, enterprises do not have to worry about cyber-security issues as the CDN service provider does it on their behalf.
Usage analytics are also provided by CDN service providers which can be used by enterprises to improve and revise various aspects of the application.
Similarly, CDNs also remove the burden of providing and deploying additional resources for scalability by eliminating the hassle of installing and running more servers when the application’s user base booms.
Challenges of CDNs
However, CDNs are not exactly a magical solution and do present challenges. The first challenge is that it is not always easy to set up and run a CDN, and it can take a considerable effort to maintain.
Additionally, the CDN architecture distributes data into many servers which most probably would not be owned by the business itself, resulting in loss of data. Moreover, content that requires continuous updates such as news headlines, shopping carts, and personalized playlists cannot rely much on CDN since data has to be updated over and over again.
CDN performs well on static data such as the content on OTT services but not for aspects that rely on dynamic data. Another issue is that certain CDNs get blocked in some countries, hence all web applications hosted on that CDN will be blocked for users in that domain.
Despite the advantages that CDN has to offer, the intense industry competition and ever-increasing user services do leave room for further optimization of services. Cloud computing offers a vast range of resources for web services and users in terms of storage, data access, bandwidth, availability, and an economical pay-as-you-go model, where there is no need to use personalized origin or surrogate servers. On the other hand, CDN speeds up the content or data delivery process. Both these technologies can be used together as Cloud Content Delivery Network or CCDN. This results in a more flexible and agile model which can quickly scale up when needed.
A CDN reduces the load on the primary or origin server with the help of caching on secondary or surrogate servers distributed around the world. This results in increased responsiveness and lower latency in web applications. Apart from the performance boost, CDN helps with cyber-security, usage analytics, and scaling.