Two servers:

• postgresql1 192.168.100.15
• postgresql2 192.168.100.20

# hostnamectl set-hostname postgresqlX
# echo '192.168.100.15 postgresql1' >> /etc/hosts
# echo '192.168.100.20 postgresql2' >> /etc/hosts
# apt-get install postgresql
# reboot

• https://perlubantuan.com/set-up-master-slave-replication-for-postgresql-9-6-on-ubuntu-16-04/