The problem with ElastiCache -- and why I rejected it as an option -- as that they make you define a 30-minute &quot;maintenance window&quot; where AWS can apply patches and reboot your cache instances.  In practice I&#x27;ve heard that this happens rarely, and when it does, the downtime is short, but it can in theory cause longer outages.<p>And in the case of both the redis and memcached backends, if the maintenance requires restarting redis&#x2F;memcached or rebooting the instance, you lose all data in the cache (at least up until your last backup).  For this particular project, that amount of downtime would easily cause a real outage for customers, and was unacceptable.