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Designing Content Delivery Network (CDN) | System Design

Last Updated : 09 Feb, 2024
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In the digital age, where online content material is king, the importance of delivering a seamless and rapid user experience can not be overstated. Content Delivery Networks (CDNs) play a vital role in attaining this aim by distributing content material strategically throughout servers globally. This article will guide you through the process of designing a Content Delivery Network.


1. What is a Content Delivery Network (CDN)?


Content Delivery Network

A Content Delivery Network (CDN) is a globally distributed network of servers designed to enhance the performance and availability of web content. CDNs reduce latency and accelerate the delivery of static assets, such as images, videos, and scripts, by storing copies on servers strategically positioned around the world. When a user requests content, the CDN automatically routes the request to the nearest server, minimizing the physical distance and, consequently, reducing load times.

2. Why use a Content Delivery Network (CDN)?

The uses of CDN are:

  1. Faster Content Delivery:
    • CDNs store copies of website content, such as images, videos, scripts, and stylesheets, on servers distributed strategically around the world. This reduces the physical distance between users and the content, leading to faster load times.
  2. Improved Website Performance:
    • By distributing content across multiple servers, CDNs help distribute the load on the origin server. This prevents overloading the server with requests, leading to improved overall website performance and responsiveness.
  3. Reduced Latency:
    • CDNs minimize latency by serving content from servers located closer to the end-users. This is especially beneficial for global audiences, as it helps prevent the delays caused by data traveling long distances over the internet.
  4. Enhanced Scalability:
    • CDNs provide scalability by offloading a significant portion of the traffic from the origin server. This allows websites and applications to handle increased user traffic, particularly during periods of high demand, without compromising performance.
  5. Bandwidth Savings:
    • CDNs help reduce the load on the origin server by caching and serving static content locally. This can lead to significant bandwidth savings for the organization hosting the content, as the CDN takes on a substantial portion of the data transfer.
  6. Distributed Security:
    • CDNs offer an additional layer of security by distributing content across multiple servers. This helps mitigate Distributed Denial of Service (DDoS) attacks, as the CDN can absorb and mitigate malicious traffic before it reaches the origin server.
  7. Load Balancing:
    • CDNs often incorporate load balancing techniques to efficiently distribute incoming traffic among multiple servers. This ensures that no single server is overloaded and helps maintain optimal performance during traffic spikes.
  8. Caching Strategies:
    • CDNs implement caching mechanisms to store frequently accessed content. This reduces the need to fetch the same content repeatedly from the origin server, leading to faster load times for users.

3. How Content Delivery Network(CDN) work?

In a Content Delivery Network, the origin server contains the original version and the edge servers are distributed across various location around the world. Below is the step by step process of how CDN’s work:

  • Content Replication:
    • Web content, such as images and videos, is duplicated and stored on multiple servers globally.
  • Geographic Distribution:
    • These servers, part of the CDN, are strategically placed in various locations around the world.
  • User Request:
    • When a user requests content, the CDN automatically determines the nearest server to fulfill the request.
  • Cache Mechanism:
    • Frequently requested content is stored on these servers, reducing the need to fetch it from the original server.
  • Load Balancing:
    • Traffic is evenly distributed among multiple servers, preventing overload on any single server.
  • Minimized Latency:
    • By serving content from nearby servers, the CDN reduces the time it takes for content to reach the user.


Let suppose when there is someone in Canada request on our website which might be hosted in USA, they will be served from the closest edge location such as the London edsge location. This much quicker than having the visitor make a complete request to the origin server which will increase the latency.


Example of CDN

4. Requirements for Content Delivery Network(CDN)

4.1 Functional Requirements for Content Delivery Network(CDN)

  • Content Distribution:
    • Define how the system will correctly distribute web content material globally. This includes techniques for replication, content material synchronization, and ensuring the present day content is to be had across all CDN nodes.
  • Caching:
    • Specify the caching approach for each static and dynamic content material. This involves figuring out what content need to be cached, for how lengthy, and the way the cache eviction policy ought to work.
  • Load Balancing:
    • Define the load balancing algorithm to evenly distribute incoming requests across CDN nodes. Consider dynamic load balancing based totally on real-time server conditions.
  • Content Purge Mechanism:
    • Describe the mechanism to invalidate or update cached content material. This involves defining the situations under which content material should be purged and how speedy the purge must propagate.

4.2 Non-Functional Requirements for Content Delivery Network(CDN)

  • Scalability:
    • Specify how the system will scale horizontally to deal with increased visitors. This could involve automatic scaling based totally on demand or a manual method for including more CDN nodes.
  • Redundancy and Reliability:
    • Define the redundancy mechanisms at diverse levels to ensure high availability. This includes techniques for data replication, failover, and backup structures.
  • Global Load Balancing:
    • Detail how global load balancing will be performed to calmly distribute traffic across CDN nodes worldwide. Consider the usage of Anycast routing for green load distribution.
  • Content Optimization:
    • Specify techniques for Content Delivery Network , consisting of image compression and minification, to enhance the rate of content delivery.
  • Mobile Optimization:
    • Describe how the CDN will optimize Content Delivery Network for mobile devicce, considering factors like responsive design and adaptive content material delivery.

5. Uses Case Diagram for Content Delivery Network(CDN)


Use Case of CDN

5.1 User:

End users who access content delivered through the CDN.

Use Cases of User:

  • Request Content: Users request content through their browsers.
  • Receive Content: Users receive content from the CDN.

5.2 Browser:

Web browsers used by end users.

Use Cases of Browser:

  • Send Content Request: Browsers send requests to the CDN for specific content.
  • Receive Content: Browsers receive and render the content received from the CDN.

5.3 Content Provider:

Individuals or organizations providing content that needs to be distributed via the CDN.

Use Cases of Content Provider:

  • Upload Content: Content providers upload their content to the CDN.
  • Configure CDN: Content providers configure settings and preferences related to the CDN.

5.4 CDN:

The Content Delivery Network responsible for distributing and delivering content efficiently.

Use Cases of CDN:

  • Cache Content: CDN caches and stores content for faster retrieval.
  • Distribute Content: CDN distributes content to end users based on their geographical location.
  • Load Balancing: CDN balances the load by distributing requests across multiple servers.
  • Monitor Traffic: CDN monitors traffic and adjusts its performance to ensure optimal content delivery.
  • Provide Analytics: CDN provides analytics and reports on content usage and performance.

6. Capacity Estimation for Content Delivery Network (CDN)

You can estimate the system capacity by analyzing certain data like traffic, number of user coming on site, storage requirements, etc. By analyzing whole data we can further calculate the required storage capacity for whole year. Here is the simplified calculation given:

Traffic is 50,000 vistors per month

Traffic per second = 50000/30*24*60*60
= 0.019

Assumption- 40% of requests served by CDN
20% of static content vs. dynamic conten

TPS – 40+20 =60
Storage required (approx 200kb/file size) = 60*200 = 12000 KB/S = 12 MB/S
Storage required per year = 12*60*60*24*365 = 378TB

7. Low-Level Design (LLD) for Content Delivery Network(CDN)

Low-level design involves unique specifications for each thing of the CDN. It interprets high level design right into a greater granular blueprint, providing a guide for developers to put into effect individual modules.


Low Level Design of CDN

7.1 Caching Module

The Caching Module in the low-level design specializes in outlining the complex information of the way the Content Delivery Network (CDN) handles content material caching. This entails specifying the caching strategy for both static and dynamic content material.

  • Static content: The design might consist of a time-based totally caching method, dictating how long content stays cached before expiration.
  • Dynamic content material: The low-level design would detail how real-time updates from the starting place server are controlled and the way the device handles cache misses, making sure the most recent content is added effectively.

The eviction regulations, including Least Recently Used (LRU) or First-In-First-Out (FIFO), are also defined to efficiently control cache space.

7.2 Load Balancing

In the low-level design section, Load Balancing is meticulously certain to make sure choicest distribution of incoming requests throughout more than one servers. This entails defining the load balancing algorithms employed, together with Round Robin, Least Connections, or Weighted Round Robin.

How Load Balancing helps in CDN?

The layout outlines how the machine monitors server health, considering elements like response times and error rates, to make knowledgeable choices in distributing visitors. Specifics on how the load balancing mechanism interacts with the CDN controller and part servers are exact to create a robust and responsive load balancing system.

7.3 Security Mechanisms

The Security Mechanisms within the low-level design consciousness on ensuring the integrity and confidentiality of the CDN. This includes specifying the safety protocols employed, with a particular emphasis on enforcing HTTPS for secure content delivery.

How machine logs protection-relate activities for auditing and analyze?

The layout outlines mechanisms for Distributed Denial of Service (DDoS) safety, inclusive of visitors filtering and rate restricting. Access controls are defined, specifying how the CDN validates and authorizes requests.

7.4 Content Delivery

The Content Delivery section of the low-level design addresses the tricky technique of retrieving content from the origin place server and distributing it to the edge servers.

Role of Content Delivery Network(CDN)

  • It info how the edge servers communicate with each other to preserve consistency in the distributed content. Specifics on how the system handles content material updates and synchronization among edge servers are described, making sure a seamless and efficient content material delivery.
  • The low-level design outlines the protocols and mechanisms for communication between edge servers and the CDN controller, emphasizing reliability and responsiveness.

8. High Level Design (HLD) for Content Delivery Network(CDN)

High-level design presents an architectural evaluation of the CDN. It makes a speciality of the interplay among important additives and the general flow of data.

8.1 Edge Servers


High Level Design of CDN

In the High-Level Design (HLD), the structure of the Content Delivery Network (CDN) is printed with a focus at the distribution of edge servers globally.

Role of Edge Server:

  • Edge servers are strategically placed in diverse geographic locations to make certain proximity to give up end-customers, thereby minimizing latency.
  • The design emphasizes the load balancing mechanism, detailing how incoming requests are successfully disbursed amongst those aspect servers.
  • The average purpose is to create a scalable and responsive network that complements the shipping of web content.

8.2 Origin Server Interaction

The HLD presents perception into how part servers interact with the starting place server. It outlines the procedure of content material retrieval from the origin server and how updates are propagated at some point of the CDN.

Role of Origin Server:

  • Strategies for minimizing latency in content material updates are highlighted, making sure that users acquire the maximum recent content successfully.
  • The design additionally addresses failover mechanisms and backup strategies to assure continuous content material availability even inside the face of origin server screw ups.

8.3 CDN Controller

Introducing a central controller, the HLD elaborates on the control and coordination of edge servers.

Role of CDN Controller

  • The CDN controller acts as the orchestrator, overseeing the overall functionality of the CDN.
  • It communicates with individual edge servers, conveying configuration adjustments, monitoring health status, and facilitating global traffic management.
  • The design emphasizes the scalability of the CDN controller, making sure it could deal with the developing needs of an increasing community.

8.4 Global Traffic Management:

The HLD illustrates how the CDN efficaciously manages global visitors via using Anycast routing.

Role of Global Traffic Management:

  • This ensures that user requests are directed to the nearest edge server primarily based on the network topology.
  • The design outlines the mechanisms in region for detecting user location and routing requests as a consequence.
  • This global traffic management approach complements the rate and reliability of content delivery, contributing to an most desirable user experience.

9. Database Design for Content Delivery Network(CDN)


9.1 Content Table

This table stores information about the content served by the CDN, including its type, location, and size.

Content_id: Unique identifier for each piece of content.
Content_name: Descriptive name or title of the content.
Content_type: Indicates the type of content (e.g., image, video, script).
Content_url: URL or path to the content on the CDN.
Content_size: Size of the content file.
Last_updated: Timestamp indicating when the content was last updated.

9.2 Edge Server Table

This table represents the edge servers in the CDN, including their location, capacity, current load, and operational status.

Server_id: Unique identifier for each edge server.
Server_location: Geographical location of the edge server.
Server_capacity: Capacity or resources of the server (CPU, RAM, storage).
Current_load: Current load or usage on the server.
Status: Operational status of the server (active, standby, offline).

9.3 User Request Table

This table logs user requests, recording details such as user ID, requested content, the edge server used, and response time.

Request_id: Unique identifier for each user request.
User_id: ID of the user making the request.
Content_id: ID of the requested content.
Request_timestamp: Timestamp indicating when the request was made.
Edge_server_used: ID of the edge server that fulfilled the request.
Response_time: Time taken to fulfill the request.

9.4 Traffic Log Table

This table stores logs related to CDN activities, providing insights into different types of requests and events.

Log_id: Unique identifier for each log entry.
Timestamp: Timestamp indicating when the log entry was created.
Request_type: Type of request (content retrieval, cache purge, etc.).
Details: Additional details about the request or event.

9.5 Cache Table

This table manages the caching information, including content ID, edge server ID, expiration details, and cache status.

Cache_id: Unique identifier for each cache entry.
Content_id: ID of the content being cached.
Edge_server_id: ID of the edge server where the content is cached.
Expiration_timestamp: Timestamp indicating when the cached content expires.
Cache_status: Status of the cache (valid, expired, purged).

10. API used for Content Delivery Network (CDN)

API Code Implementation

Add New Content API (POST) Request:

  • Endpoint: /api/content
  • Description: Allows administrators to add new content to the CDN.


  "content_url": "",
  "origin_server": "",
  "cache_duration": 3600  // Cache duration in seconds


  "status": "success",
  "message": "Content added to CDN successfully",
  "content_id": "c12345"

Retrieve Content Details API (GET) Request:

  • Endpoint: /api/content/c12345
  • Description: Retrieves details of a specific content item from the CDN.


GET /api/content/c12345
Accept: application/json


HTTP/1.1 200 OK
Content-Type: application/json
  "content_id": "c12345",
  "content_url": "",
  "origin_server": "",
  "cache_duration": 3600,
  "last_modified": "2023-03-15T08:30:00Z",
  "popularity": 1200  // Number of times accessed

Update Content API (PUT) Request:

  • Endpoint: /api/content/c12345
  • Description: Allows administrators to update details of existing content in the CDN.


PUT /api/content/c12345
Content-Type: application/json
  "cache_duration": 7200  // Updated cache duration in seconds


HTTP/1.1 200 OK
Content-Type: application/json
  "status": "success",
  "message": "Content updated successfully",
  "content_id": "c12345"

11. Microservices used for Content Delivery Network (CDN)


Microservices for CDN

11.1 Edge Service

The Edge Service in the Microservices and APIs Used section of the design specializes in dealing with content caching, retrieval, and delivery.

  • The layout specifies the API for conversation with the CDN controller, making an allowance for seamless coordination.
  • The edge provider microservice is accountable for dealing with content material at the edge servers, making sure efficient caching strategies, and responding to user requests with minimal latency.

11.2 Load Balancer Service

This microservice is devoted to load balancing and distributing incoming requests among area servers.

  • The layout elaborates at the APIs exposed by the Load Balancer Service, detailing the way it dynamically adjusts the distribution of traffic based totally on server health and different metrics.
  • The microservice guarantees even usage of resources and prevents any single server from becoming a bottleneck.

11.3 Security Service

The Security Service microservice is responsible for imposing security features together with DDoS safety and access controls.

  • The layout outlines the APIs used for validating and authorizing requests, ensuring that the CDN keeps a secure environment for content delivery It specializes in the modularity of security functions to permit for destiny enhancements or adjustments.

11.4 Analytics Service

The Analytics Service microservice is designed to collect and procedure overall performance metrics.

  • The design specifies the APIs for gaining access to analytics information, taking into consideration real-time tracking and evaluation of CDN performance.
  • This microservice contributes to statistics-driven selection-making, enabling continuous optimization and upgrades in content material delivery.

12. Scalability used for Content Delivery Network(CDN)

  • Horizontal Scaling:
    • The Scalability section of the design focuses on the strategies employed for horizontal scaling.
    • It outlines mechanisms for dynamically adding more aspect servers to the CDN to address elevated traffic masses.
    • The layout emphasizes the importance of load balancing in dispensing requests evenly throughout these servers, ensuring optimal resource utilization.
  • Vertical Scaling:
    • Vertical Scaling is addressed by way of specifying how individual servers can be upgraded to deal with ¬†higher loads.
    • The design outlines auto-scaling mechanisms that dynamically adjust sources (CPU, RAM) primarily based on demand.
    • This ensures that the CDN can adapt to varying levels of site visitors without sacrificing overall performance.
  • Stateless Design:
    • The design emphasizes the significance of a stateless layout to obtain seamless scalability.
    • Stateless structure allows any edge server to handle any consumer request with out counting on session-precise statistics stored domestically.
    • This design choice allows flexibility in adding or removing of servers without impacting user sessions, contributing to the overall scalability of the CDN.

13. Conclusion

Designing a Content Delivery Network includes careful consideration of objectives, content kinds, geographical distribution, and security features. By strategically setting edge servers, enforcing efficient caching mechanisms, and constantly optimizing overall performance, a properly-designed CDN can significantly enhance the user experience and make a contribution to the fulfillment of online structures in modern speedy-paced world.

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