Passenger, Plesk and Node.js: address already in use - node.js

Question

My question is about getting Phusion Passenger and Plesk Onyx 17.5.3 to work together nicely. I have a new server running Ubuntu 16.04.
I am following the official Phusion Passenger tutorial on deploying a Node.js app, and I have followed it successfully to the point where I need to tell Passenger to listen on port 80.
Here are my steps:
With my registrar, I set up a DNS entry for the subdomain pass.domain.com
In the Plesk interface, I define the new subdomain
If I visit http://pass.domain.com in my browser, I get the default Plesk web page.
I follow the "Phusion Passenger: Node.js tutorial" until I reach this command:
sudo passenger start --port 80 --user someusername --environment production --daemonize
Note: I am using a valid custom user name in the place of `someusername'.
I get this error:
Could not start the Nginx engine:
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] still could not bind()
It appears that Plesk is already serving the default web page at this address, so Phusion Passenger cannot access it. What files do I need to add or edit to get Plesk to release the address so that Passenger can use it?
EDIT 4: I have found this question which describes similar symptoms. However the OP is using Meteor Up and I am using Passenger. His solution was to get Meteor Up to tell Node.js to run on port 3001, and get nginx to listen on port 80 and proxy requests to port 3001. I had understood that Phusion Passenger already does something similar under the hood.
Is there a way to modify the passenger start command to clarify this?
OLDER EDITS
EDIT 1: In response to #TarunLalwali, here is the output of sudo netstat -plnat on this server:
$ sudo netstat -plnat
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:4190 0.0.0.0:* LISTEN 15234/dovecot
tcp 0 0 127.0.0.1:12768 0.0.0.0:* LISTEN 15654/psa-pc-remote
tcp 0 0 0.0.0.0:993 0.0.0.0:* LISTEN 15234/dovecot
tcp 0 0 0.0.0.0:995 0.0.0.0:* LISTEN 15234/dovecot
tcp 0 0 127.0.0.1:27017 0.0.0.0:* LISTEN 2293/mongod
tcp 0 0 0.0.0.0:110 0.0.0.0:* LISTEN 15234/dovecot
tcp 0 0 0.0.0.0:143 0.0.0.0:* LISTEN 15234/dovecot
tcp 0 0 127.0.0.1:783 0.0.0.0:* LISTEN 1315/.spamassassin
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 26659/nginx
tcp 0 0 0.0.0.0:8880 0.0.0.0:* LISTEN 23894/config
tcp 0 0 0.0.0.0:465 0.0.0.0:* LISTEN 2142/master
tcp 0 0 172.17.0.1:53 0.0.0.0:* LISTEN 17312/named
tcp 0 0 94.76.206.212:53 0.0.0.0:* LISTEN 17312/named
tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 17312/named
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1413/sshd
tcp 0 0 0.0.0.0:3000 0.0.0.0:* LISTEN 12563/passenger-sta
tcp 0 0 127.0.0.1:953 0.0.0.0:* LISTEN 17312/named
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 2142/master
tcp 0 0 94.76.206.212:443 0.0.0.0:* LISTEN 26659/nginx
tcp 0 0 0.0.0.0:8443 0.0.0.0:* LISTEN 23894/config
tcp 0 0 94.76.206.212:993 92.130.47.95:49994 ESTABLISHED 15322/imap-login
tcp 0 0 127.0.0.1:51168 127.0.0.1:12768 TIME_WAIT -
tcp 0 0 94.76.206.212:25 200.188.141.75:51400 TIME_WAIT -
tcp 0 188 94.76.206.212:22 92.130.47.95:34414 ESTABLISHED 4035/sshd: blacksla
tcp6 0 0 :::4190 :::* LISTEN 15234/dovecot
tcp6 0 0 :::993 :::* LISTEN 15234/dovecot
tcp6 0 0 :::995 :::* LISTEN 15234/dovecot
tcp6 0 0 :::7080 :::* LISTEN 26432/apache2
tcp6 0 0 :::7081 :::* LISTEN 26432/apache2
tcp6 0 0 127.0.0.1:3306 :::* LISTEN 10040/mysqld
tcp6 0 0 :::106 :::* LISTEN 1532/xinetd
tcp6 0 0 :::110 :::* LISTEN 15234/dovecot
tcp6 0 0 :::143 :::* LISTEN 15234/dovecot
tcp6 0 0 ::1:783 :::* LISTEN 1315/.spamassassin
tcp6 0 0 2a02:af8:1:900::3860:80 :::* LISTEN 26659/nginx
tcp6 0 0 :::8880 :::* LISTEN 23894/config
tcp6 0 0 :::465 :::* LISTEN 2142/master
tcp6 0 0 :::53 :::* LISTEN 17312/named
tcp6 0 0 :::21 :::* LISTEN 1532/xinetd
tcp6 0 0 :::22 :::* LISTEN 1413/sshd
tcp6 0 0 :::25 :::* LISTEN 2142/master
tcp6 0 0 2a02:af8:1:900::386:443 :::* LISTEN 26659/nginx
tcp6 0 0 :::8443 :::* LISTEN 23894/config
Note: I have already asked about this issue on the Plesk forum, but it has received no response. I am hoping that asking the Phusion Passenger community here will be more productive. Once I have a working solution, I will post a link from the Plesk forum to the answer here.
Thanks in advance for your insights,
James
EDIT 2: Following #TarunLalwali's advice, I tried stopping nginx, but this produced an unknown error:
$ sudo nginx -s stop
$ sudo passenger start --port 80 --user node --environment production --daemonize
Could not start the Nginx engine:
nginx: [alert] Unable to start the Phusion Passenger watchdog because it encountered the following error during startup: Unable to start the Passenger core: it seems to have crashed during startup for an unknown reason, with exit code 1 (-1: Unknown error)
EDIT 3: Attempting to disable nginx server-wide before invoking Passenger:
$ sudo systemctl disable nginx
Synchronizing state of nginx.service with SysV init with /lib/systemd/systemd-sysv-install...
Executing /lib/systemd/systemd-sysv-install disable nginx
insserv: warning: current start runlevel(s) (empty) of script `nginx' overrides LSB defaults (2 3 4 5).
insserv: warning: current stop runlevel(s) (0 1 2 3 4 5 6) of script `nginx' overrides LSB defaults (0 1 6).
$ systemctl status nginx
* nginx.service - Startup script for nginx service
Loaded: loaded (/lib/systemd/system/nginx.service; disabled; vendor preset: enabled)
Active: inactive (dead)
$ sudo passenger start --port 80 --user node --environment production --daemonize
Could not start the Nginx engine:
nginx: [alert] Unable to start the Phusion Passenger watchdog because it encountered the following error during startup: Unable to start the Passenger core: it seems to have crashed during startup for an unknown reason, with exit code 1 (-1: Unknown error)

Answer 1

You mention that you need the system Nginx (at port 80) to run other subdomains on the server.
Passenger Standalone can coexist peacefully with a system Nginx using two steps:
Run it on a non-conflicting port, for example the default 3000:
sudo passenger start --port 3000 --user someusername --environment production --daemonize
For the domain that you want Passenger to server, tell the system Nginx to proxy to Passenger.
proxy_pass http://localhost:3000;
Remember to reload/restart Nginx to activate the config.
How to do step 2 exactly in Plesk is a question best asked on the Plesk forum, but from the Passenger point of view this setup should work.