CDN performance monitoring and troubleshooting are vital for maintaining website speed and reliability. Key metrics include cache hit ratio, response time, bandwidth usage, error rates, and TTFB. Monitoring tools include CDN provider dashboards, third-party services like Catchpoint and ThousandEyes, synthetic tests, and RUM. Common issues are cache invalidation, origin server problems, regional performance gaps, SSL/TLS errors, and traffic spikes. Effective troubleshooting involves verifying the issue, checking CDN status, analyzing metrics, and testing different locations. Best practices include using proper Cache-Control headers, content versioning, and maintaining performance baselines. Escalate to the CDN provider for unresolvable or complex issues. Proactive strategies minimize downtime and enhance user experience.