Configure PostgreSQL to allow remote connections

Prepare a centos7 operating system with PostgreSQL Database installed. If not, see here.

Configure the postgresql.conf . file

Find the path containing the file postgresql.conf
#find / -name “postgresql.conf“

Access the path and edit the file like so
#vi /var/lib/pgsql/11/data/postgresql.conf

find the line #listening_addresses=’localhost’ , #port=5432 and adjusted like a star
listening_addresses=’*’
port=5432

'*' means it will listen on all ip addresses if you want to listen with 1 or several ip addresses, you can replace the * sign with the ip address you want, each ip separated by comma

Configuration file pg_hba.conf

Find the file path pg_hba.conf

#find / -name “pg_hba.conf”

Access the path and edit the file like so
# vi /var/lib/pgsql/11/data/pg_hba.conf

Add the following line at the end of the file
host all all 0.0.0.0/0 md5 –> all ip addresses can connect to postgresql.

(md5 is the password authentication mode, if you don't want to authenticate with a password, then replace it md5 is equal to trust).
host all 103.121.88.143/24 md5 –> only allow ip addresses in range 192.168.3.12/24

Firewall configuration on centos7
Open port 5432 on centos7's firewalld firewall
#firewall-cmd –zone=public –add-port=5432/tcp –permanent
#firewall-cmd –relead

Check if the port is open
firewall-cmd –zone=public –list-port
Allow to add wan ip address on firewalld firewall to allow ip to connect remotely (get wan ip address) here).
#firewall-cmd –permanent –zone=public –add-source=192.168.100.1
#firewall-cmd –relead

Check to see if it has been added
#firewall-cmd –zone=public –list-all

Login to check
Here use another vps with ip like in the file settings pg_hba.conf to test the connection to postgresql server configured by me trust So when you log in, you don't need to confirm the password.