migrate a postgres db
# dumping
$ docker exec -t <old_hostname> pg_dump --no-owner --no-acl -U <old_user> <old_db> > dump.sql
# creating new db
CREATE DATABASE <new_db> TEMPLATE template0;
ALTER DATABASE <new_db> OWNER TO <new_user>;
# restore
$ docker exec -i <new_hostname> psql -U <new_user> -d <new_db> < dump.sql