Synthetic Monitor Timeouts Traced to Queue Waits and Burstable Servers, Not Scripts

An engineering team found that dozens of browser-based synthetic monitors were timing out despite working scripts and seemingly healthy servers. A query showed average external queue wait was about 9.2 minutes, roughly seven times longer than actual execution time, meaning checks were waiting to start rather than running slowly. The investigation pointed to a fleet of eight burstable t2.large instances offering too few concurrent check slots, with demand sitting at roughly full capacity. Queue delays rise sharply as utilization nears 100%, which amplified a small capacity shortfall into severe waits. The team replaced the eight small instances with four larger, non-burstable m6i.xlarge instances, which provides more total concurrent capacity.