Memcached is a general-purpose distributed memory caching system. It is used to speed up dynamic database-driven websites by caching data and objects in RAM to reduce the number of times an external data source must be read.
Memcached is a memory cache demon that can be used by most OpenStack services to store ephemeral data, such as tokens.
Access to Memcached is not handled by HAProxy because replicated access is currently in an experimental state. Instead, OpenStack services must be supplied with the full list of hosts running Memcached.
The Memcached client implements hashing to balance objects among the instances. Failure of an instance impacts only a percentage of the objects and the client automatically removes it from the list of instances. The SLA is several minutes.