Design of a Client-Side Monitoring System

A server cannot log a request that never arrives. External probes and client telemetry provide additional views of DNS, routing, and last-mile failures, each with its own coverage and reporting limits.

Initial design

Deploy probers at selected network and geographic vantage points to make scheduled requests. Record which stage fails, such as name resolution, connection establishment, or the application response. The result describes reachability from that vantage point at that time.

Issues with probers

External probers face several limitations: