Multi-CDN Strategy & Failover Flashcards

A financial services firm requires that its multi-CDN failover completes within 30 seconds of detecting a CDN failure. Which combination of settings best achieves this?

Answer: DNS TTL of 30s + health check interval of 10s with 3-failure threshold

A 30-second DNS TTL and 10-second health check interval with a 3-failure threshold allows failover detection and DNS propagation to complete within the 30-second SLA window.

Which approach best prevents cache poisoning attacks when operating a multi-CDN environment with multiple origin-pull paths?

Answer: Validate all origin responses with TLS certificate pinning and enforce strict Cache-Control headers

TLS certificate pinning between CDN and origin verifies server identity, while strict Cache-Control headers prevent unauthorized content from being cached and served.

A multi-CDN deployment uses JavaScript-based RUM to measure CDN performance. Which limitation must operators account for when using this approach?

Answer: RUM data is skewed by users with ad blockers or script-blocking browser extensions who may not report metrics

Ad blockers and privacy tools often block RUM beacon requests, creating a self-selection bias where performance data underrepresents a subset of users.

What is the purpose of 'last-resort' origin failover configuration in a multi-CDN architecture?

Answer: To ensure user requests reach the origin server directly if all CDN providers simultaneously fail

A last-resort origin failover path guarantees site availability even in catastrophic multi-CDN failure scenarios by allowing direct origin access.

A multi-CDN operator wants to test failover procedures without impacting production users. Which technique allows this?

Answer: Simulate failover in a staging environment with identical CDN configurations and traffic patterns mirrored from production

A staging environment with mirrored production CDN configurations allows realistic failover testing without risking real user sessions.

Which CDN configuration error most frequently causes request loops in a multi-CDN setup where CDN-A pulls from CDN-B as its origin?

Answer: CDN-B is configured to pull from CDN-A as its origin, creating a circular dependency

A circular origin-pull configuration where CDN-A pulls from CDN-B and CDN-B pulls from CDN-A results in infinite request loops and total cache miss.

An organization needs to attribute CDN cost accurately when using two providers. CDN-A bills per GB transferred and CDN-B bills per request. Which monitoring data is essential for cost forecasting?

Answer: Per-CDN byte transfer volume AND per-CDN request count, broken down by traffic type and region

Accurate cost forecasting requires per-CDN breakdowns of both bytes transferred and request counts, since each provider uses a different billing dimension.