Extremely hard to scale in what sense? A single redis server running on fairly commodity hardware can serve some pretty intense loads (10s of thousands of ops/s

Extremely hard to scale in what sense? A single redis server running on fairly commodity hardware can serve some pretty intense loads (10s of thousands of ops/sec). Once "scale" bigger than that is an issue, companies should already have in place the development staff that will ensure scaling up is done in a sane way, i.e., that have enough sense and/or experience to choose the correct tools for the job. Redis is one such tool--its clustering "story" may not be ideal but even a small, minimal cluster will be more than sufficient for any use-case that a distributed memory cache is fit for at a scale that will cover 99% of business' needs.