Description of problem:

In OSp13 and below, it used to be possible to ExtraConfig this in your templates:
   keystone::memcache_servers: "%{hiera('memcached_servers')}"

e.g:
parameter_defaults:
  ExtraConfig:
    keystone::cache_enabled: true
    keystone::memcache_servers: "%{hiera('memcached_servers')}"
    keystone::cache_backend: oslo_cache.memcache_pool
    keystone::token_caching: true

memcached_servers returned the proper URI list for either 1) or 3) controllers.

On OSP16.1, memcached_servers is no longer provided in hiera data, meaning the only way to configure memcached_servers for keystone is to explicitly provide the IPs:

parameter_defaults:
  ExtraConfig:
    keystone::cache_enabled: true
    keystone::cache_memcache_servers: 192.168.1.1:11211,192.168.1.2:11211,192.168.1.3:11211
    keystone::cache_backend: oslo_cache.memcache_pool
    keystone::token_caching: true

So, unless you're using fixed IPs, there is no way to know the Memcached IPs -before- deployment, thus requiring a 2nd deploy/stack update to set the value of keystone::cache_memcache_servers.

The closest hiera record would be memcached_node_ips but it doesn't include the :11211 part and would need processing before it could be used.

Please bring back hiera('memcached_servers' so we can use it in our templates with a single deploy!