6.10 Failure Stances and Shared Defenses

Most defenses against Redis failures repeat from one pattern to the next. The previous lesson walked through how the online shop's uses of Redis fail: the product cache sends its full load to the database, sessions fail as a mass logout, the rate limiter must fail open or closed, locks can grant twice, and queues can lose or strand jobs. It also named the three stances a feature can take: fail open, fail closed or degrade.