I have a database topology as in the picture attached below and postgresql9.6 is installed in all the machines. It is master-slave architecture with sharding. I have successfully configured master-slave replication and automatic failover using repmgr/repmgrd. But i am confused on how to achieve sharding in this scenario. I have tried citus extension, but for the table structure i have citus does not support sharding, here is the link. Can anyone suggest me how can i achieve sharding in this scenario.

Database topology: