*almost always: https://blog.cloudflare.com/details-of-the-cloudflare-outage-on-july-2-2019/ https://blog.cloudflare.com/details-of-the-cloudflare-outage... >T

*almost always: https://blog.cloudflare.com/details-of-the-cloudflare-outage-on-july-2-2019/ https://blog.cloudflare.com/details-of-the-cloudflare-outage... >The Lua WAF uses PCRE internally and it uses backtracking for matching and has no mechanism to protect against a runaway expression. https://blog.cloudflare.com/making-the-waf-40-faster/ https://blog.cloudflare.com/making-the-waf-40-faster/ >Back in July 2019, the WAF transitioned from using a regular expression engine based on PCRE to one inspired by RE2, which is based around using a deterministic finite automaton (DFA) instead of backtracking algorithms. This change came as a result of an outage where an update added a regular expression which backtracked enormously on certain HTTP requests, resulting in exponential execution time. >After the migration was finished, we saw no measurable difference in CPU consumption at the edge, but noticed execution time outliers in the 95th and 99th percentiles decreased, something we expected given RE2's guarantees of a linear time execution with the size of the input.