Architecture

CloudFront uses a global network of Points of Presence (PoPs) and Regional Edge Caches (RECs), providing global access for your viewers. AWS continues to extend CloudFront based on growth and anticipated customer needs. Availability is one of the high-priority design tenets of CloudFront. Metropolitan areas have the highest concentration of traffic, and CloudFront provides multiple edge locations for scale and performance. These locations are deployed in different facilities to provide a high degree of resilience. A cluster of edge locations in a single area gives CloudFront the ability to route viewers quickly to another location in close proximity without noticeable performance impact.

CloudFront edge locations have multiple connections to local Internet Service Providers (ISPs) and global carriers through internet exchanges and direct private fiber connections. This minimizes video delivery latency, reduces probability of congestion and traffic loss, and provides high availability. Edge locations also leverage the AWS global network, which connects AWS Regions and edge locations.

The AWS global network provides high bandwidth, resilience and redundancy at scale. This gives you consistent performance, high availability and shields your viewers from internet instabilities and changing conditions.

The quality of the connection from the origin to the edge location is just as important as the proximity of the edge location to the viewer, providing low latency and avoiding re-buffering, which is a factor in reducing viewer churn. AWS works closely with our customers to understand their current and future traffic patterns to guide further expansion with new edge locations and scaling of existing locations. This can be particularly relevant when planning the launch of your video platform in a new geographic region or anticipating high peak events.

The CloudFront architecture includes a mid-tier caching layer between your origin and the edge locations. This allows you to scale further without a corresponding increase in load at the origin, and to maintain a high cache hit ratio. This mid-tier layer is known as a Regional Edge Cache (REC). Upon a cache miss, an edge location will initiate a request to its associated REC before going to the origin. The REC adds a layer of content consolidation where the volume of requests going to the origin is reduced as requests for the same content from different edge locations can be retrieved from the same REC. RECs can increase a video streaming object's retention time due to its larger cache storage and this provides another advantage of using CloudFront for large VOD video catalogs.

Figure 2 – Amazon CloudFront architecture

CDN requirements for media delivery often extend beyond performant and scalable delivery to the viewers. Media applications often adapt the content for different viewers or device platforms, provide security controls for paywall content, or add other customizations based on the request from the viewer.

You can write your own code to further customize the processing of HTTP requests and responses by associating an edge function with your CloudFront distribution. To minimize latency, edge functions will run close to your viewers. You can select from two different types of edge functions based on your use case:

• For complex, compute-heavy use cases, Lambda@Edge gives you the ability to run JavaScript or Python code in a regional edge cache, usually in the AWS Region closest to the CloudFront edge location that received the viewer request. Examples of using Lambda@Edge in media delivery include filtering live streaming renditions by device type at the Edge and on-the-fly video conversion from MP4 to HLS. For additional examples, see Lambda@Edge example functions in the CloudFront Developer Guide.

• For lightweight, latency-sensitive use cases, CloudFront Functions can be used to execute lightweight JavaScript code at CloudFront edge locations at approximately one-sixth of the price of Lambda@Edge. Some common use cases for CloudFront Functions are cache-key manipulations and normalization, URL rewrites and redirects, HTTP Header manipulation, and access authorization. For more examples, see Example code for CloudFront Functions.