Currently service operators are configured as below when running with tls disabled and ipv6 enabled:-

[cache]
backend = dogpile.cache.memcached
enabled=true
memcache_servers=memcached-0.memcached.openstack.svc:11211,memcached-1.memcached.openstack.svc:11211,memcached-2.memcached.openstack.svc:11211
tls_enabled=false

But with this config services(for ex keystone/neutron) do not work or take too much time to respond and hit the api timeout.

When backend is "dogpile.cache.memcached" and memcache serving over IPv6 it requires memcache_servers to contain inet6: prefix as described in https://review.opendev.org/c/openstack/puppet-tripleo/+/833711/11/manifests/profile/base/keystone.pp

With TLS enabled, issue is not seen as "dogpile.cache.pymemcache" backend is configured and that do not require inet6: prefix.

It got missed when TLS support was enabled https://issues.redhat.com/browse/OSPRH-5283

This Epic is to track the fix of the issue.