Architecture

Synopsis Multi-CDN architectures commonly use DNS steering, a layer 7 proxy or aggregator, client-side selection, or a hybrid. Each pattern changes failure behavior, latency, and operational complexity, so the selection must follow the workload and its recovery requirements. 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 defines multi-CDN and explains when the approach improves service outcomes. It describes benefits in availability, performance, and vendor risk, and it outlines added complexity in operations, security, and cost. A simple decision framework and a migration overview provide a practical start point. Definition Multi-CDN is the practice of serving the same property through more than one content delivery network under a single control plane. Requests are routed to one of several providers based on policy. Policies consider jurisdiction, health, performance, and cost in that order of precedence. Correctness and user experience remain the primary constraints. ...