PG comparator is a perl script that compares tables between two databases instances, generates a diff and applies it on the destination table.
./pg_comparator --checksum-function=md5 -S -D “pgsql://UUUUUUU:XXXXXXXX@10.1.200.2/DBNAME/TABLENAME?id” pgsql://uuuuuuu:xxxxxx@testdb.1234.eu-central-1.rds.amazonaws.com:5432/testdb