Routing

Multi-CDN and Dynamic Site Acceleration (DSA) are both strategies to make content delivery faster and more reliable. They are often mentioned together, but they tackle different parts of the problem. Multi-CDN chooses between providers, while DSA focuses on optimizing the transport path between the CDN edge and the origin. What DSA Does Dynamic Site Acceleration was introduced in the 2000s as a premium CDN feature. It targets dynamic content that cannot be cached. Instead of improving speed through storage at the edge, DSA makes the path between the edge and the origin faster. ...

Synopsis This chapter describes the main architecture patterns for multi-CDN and how to choose between them. It explains DNS-based steering, layer 7 proxy or aggregator designs, client-side selection, and hybrid approaches. It focuses on behavior, failure modes, latency impact, and operational complexity. DNS-based steering Authoritative DNS answers with records that point to different CDNs based on geography, network, or other criteria. This pattern has low per-request overhead because the routing decision happens before HTTP, but it reacts on the scale of DNS caching. Time to live and resolver behavior affect how quickly changes take effect. Geo and ASN databases must be maintained. Health-driven routing requires either short TTLs or resolver-aware mechanisms that may not be consistent across networks. DNS steering is simple to deploy and scales well, but it is limited in how fast it can respond to sudden failures and it has coarse visibility into per-request signals. ...

Synopsis This chapter explains how to design and operate traffic steering for multi-CDN. It covers inputs and data quality, common policy types, precedence rules, health and failover, stability controls, cost awareness, and rollout practices. Inputs and data Effective policies need inputs that reflect user experience and provider health. Synthetic measurements provide controlled and repeatable data but can miss last mile conditions. Real user measurements capture actual paths and networks but require sampling, privacy controls, and careful aggregation. Health signals from providers are useful but should not be trusted without verification. Logs and metrics from the service stack provide the ground truth for outcomes. ...