In order to connect a memcache client to MemCachier, you use a username and password listed on the analytics dashboard for your cache. Each cache can have multiple sets of credentials. One of these sets of credentials is distinguished as primary, meaning that, for hosted platforms like Heroku, it is linked to the hosted platform MemCachier addon.
From the Credentials panel on the analytics dashboard, it is possible to create new credentials, delete existing credentials and promote secondary credentials to primary credentials. This makes it possible to rotate credentials by creating a new set of secondary credentials and promoting them to primary. For caches associated with hosted platforms, promoting a set of secondary credentials to primary causes the configuration variables on the hosted platform to be updated. For example, rotating the credentials on a Heroku-associated cache causes an update of the MEMCACHIER_USERNAME and MEMCACHIER_PASSWORD configuration variables on your Heroku app and a restart of your dynos to pick up the new values.
Each set of credentials for a cache can be given different capabilities, in the sense that sets of credentials can be restricted to read-only access to the cache, or prevented from flushing the cache via the memcache API. These capabilities are controlled by checkboxes on the Credentials panel of the analytics dashboard. (The exact error conditions that a client will receive if it attempts to perform an action for which it does not have the capability depends on the details of the client library used. The most common cases are likely to be for the Dalli Ruby library and the pylibmc Python library. For both of these client libraries, attempting to set a cache entry using credentials that do not have the write capability will simply result in a “value not set” response from the library.)