MySQL sharding and stored procedures
Off the wall...


Turn the Procedure into a function.  Simply return 0, or something irrelevant.
Instead of CALLing the Procedure, invoke the Function this way:

SELECT 0 WHERE key = 'A' AND routine(key);


The hope is that the sharding will kick in for the first part of the WHERE and send the SELECT only to the desired shard.

BTW, it appears that Fabric is being decommissioned.