Reliability

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 provides standard playbooks for incidents in multi-CDN environments. It covers detection, triage, scoping by geography and network, isolation and reroute choices, change control during active events, communication, restoration, and post-incident analysis. The objective is to protect users first, keep changes reversible, and leave an audit trail that improves future responses. Principles Incident handling favors user outcomes over internal metrics. Actions modify the smallest scope that achieves protection. All changes must be reversible. Each action records who acted, what changed, and why. Telemetry drives decisions and distinguishes symptoms from causes. Providers are treated as interchangeable routes unless a risk register documents exceptions. ...

Synopsis This chapter explains how changes to routing, configuration, and content are tested and deployed in a multi-CDN environment. It covers pre-production validation, cohort design, canary strategies, progressive exposure, measurement, guard rails, rollback, and record keeping. The goal is to make changes reversible, observable, and limited in blast radius. Purpose and scope Multi-CDN adds variables at several layers. DNS answers, proxy behavior, client logic, cache identity, and origin controls can all change outcomes. Testing must isolate causes and confirm improvements using indicators that reflect user experience. Rollouts must keep a safe default path and apply controls that prevent fast spread of harm. ...

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. ...

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. ...