Worker isolation is a defensive architecture that separates risky tasks, such as parsing uploaded spreadsheets or other untrusted files, from the main application process. Instead of letting the core web service handle the file directly, the job runs in a dedicated worker thread, process, container, or queue-backed service with tighter limits and fewer privileges.
This matters because document parsers can hang, crash, or consume excessive CPU when they encounter maliciously crafted input. If parsing is isolated, a stuck worker is easier to restart, throttle, or kill without taking down the whole application. In practice, defenders combine isolation with timeouts, request limits, CPU and memory caps, and circuit breakers. Attackers try to exploit the opposite design: if untrusted files are processed in shared core threads, one bad file can block resources and cause a denial of service. Worker isolation turns that failure mode from service-wide outage into a contained, recoverable incident.