AWS Lightsail Firewall doesn't open a port or something else is blocking it

Question

Hello,   
The Lightsail Firewall is unable to open a specific port, I searched for this issue in the forums and there are several issues like this one but none of them has a valid solution for me.  
I'm setting up my first Lightsail instance with Ubuntu 20.04 LTS and already installed Odoo and Postgresql. In the Lightsail firewall I opened 2 additional ports for any IP address: 8069 for the Odoo application and 5432 for PostgreSQL. I can access the Odoo application but I am unable to access the PostgreSQL service. I'm trying to open the PostgreSQL port (5432) on Networking > Firewall section (I did the same for the 8069) but seems it doesn't take any effect. I tried https://www.yougetsignal.com/tools/open-ports/ to test if the port is OPEN or CLOSED. Both public and private IP Port 22, 80 and 8069 are open. I’m pretty sure that there is a local firewall blocking incoming connections, in which case opening the port through the Lightsail firewall isn't sufficient. I tried connecting to the port locally from the server with “telnet 127.0.0.1 5432” and worked, but the same command using the external IP address didn’t.   
I listed the active services running and ufw is active but “sudo ufw status” says inactive, so ufw is running but not blocking anything (I hope). I don’t identify any other service as a firewall (my only suspect is apparmor but I don't know how it works)  
service --status-all  
  +   acpid : Advanced Configuration and Power Interface (ACPI) event daemon  
  +   apparmor : Linux kernel security module  
  +   apport : Apport intercepts Program crashes,  
  +   atd : runs jobs queued  
  -   console-setup.sh  
  +   cron : scheduler  
  -   cryptdisks  
  -   cryptdisks-early  
  +   dbus : message bus daemon  
  +   grub-common : Bootloader  
  -   hibagent  
  -   hwclock.sh  
  -   irqbalance  
  -   iscsid  
  -   keyboard-setup.sh  
  +   kmod : control kernel  
  -   lvm2  
  -   lvm2-lvmpolld  
  +   multipath-tools : configure multiple I/O paths between server nodes and storage arrays  
  +   odoo : Application  
  -   open-iscsi  
  -   open-vm-tools  
  -   plymouth  
  -   plymouth-log  
  +   postgresql : Database  
  +   procps : utilites for pseudo-filesystem  
  -   rsync  
  +   rsyslog : for logging  
  -   screen-cleanup  
  +   ssh  
  +   sysstat : system stats  
  +   udev : device management  
  +   ufw : <<

Answer

In addition to the two files you already mentioned, have you also taken a look at whether your settings are being overridden by config in postgresql.auto.conf? Settings in postgresql.auto.conf will override those in postgresql.conf (more docs about that config file here: https://www.postgresql.org/docs/13/config-setting.html#CONFIG-SETTING-CONFIGURATION-FILE).  
  
A cursory Google search also turns this up, if this helps: https://dba.stackexchange.com/questions/180177/postgres-seems-to-ignore-listen-addresses-setting

Answer

I just found out the problem. To make PostgreSQL available to an external IP there are two items to configure: postgresql.conf and pg_hba.conf. Some sort of script or whatever is commenting out the line with the Public IP address in the postgresql.conf. When I restart the PostgreSQL service, I can connect from my local PGAdmin4, but if I reboot the instance, "something" is commenting the line with the Public IP address. Now I have to find the guilty "something", I think I can figure it out.

AWS Lightsail Firewall doesn't open a port or something else is blocking it

Relevant content