Readable row key cassandra

Readable row key cassandra

We are investigating migrating a system from a RDBMS to Cassandra and are
having trouble finding a way to convert auto-increment column to
Cassandra. We actually have no need for this to be sequential at all, it
can even contain characters, but it must be short (ideally under 8 chars)
and globally unique. Ideal value would look something like
AB123456
First part of the question is should we be generating this key in
application code or in Cassandra?
Second part: If Cassandra, how?
If Application code, is it an acceptable pattern to generate a candidate
code then attempt an insert, if collision occurs then regenerate key
candidate and retry?