Cannot deploy a ruby udp server and open port on ubuntu droplet

Posted November 12, 2021 142 views
NetworkingDeploymentUbuntu 18.04

Hi. I have a working ruby 2.7.2 app that is a simple udp server on my local development machine which uses the ruby UDPSocket library. I have created a ubuntu 18.04 droplet and created a cloud firewall with a custom inbound rule protocol:udp, port range:7373. I have created a non-sudo user (m32udp) and placed the app in /var/www/m32udp/code directory with these privilages.

m32udp@megazoic:/var/www/m32udp/code$ ls -l
total 24
-rw-r–r– 1 m32udp m32udp 60 Nov 11 22:56 Gemfile
-rw-r–r– 1 m32udp m32udp 100 Nov 11 23:51 Gemfile.lock
-rw-r–r– 1 m32udp m32udp 368 Nov 11 22:56 client.rb
-rw——- 1 m32udp m32udp 115 Nov 12 01:14 nohup.out
-rw-r–r– 1 m32udp m32udp 2194 Nov 11 22:56 server.rb

My ruby code (abbreviated) is

    @socket =
    @socket.bind("", @port)

I have also tried entering my droplet’s ip address in the bind parameter. Also @port is 7373.

When I start the app as m32_udp user, netstat reports…

watchdog@megazoic:~$ netstat -an
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State

tcp 0 0* LISTEN

tcp 0 0* LISTEN

tcp6 0 0 :::22 :::* LISTEN

udp 0 0*

udp 0 0*

When I change the ruby code in my app to


netstat reports

udp 0 0*

In either case, I cannot see this port as being open using netcat from another machine. It is also not reported as LISTEN in netstat. Do I need to run this app with sudo privileges? Do I have the ip address correct in the bind statement?
Thanks for any help that you can provide!

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1 answer

My bad. This was working with the original socket.bind call using

I guess that I expected netstat to report LISTEN for this port as my app was indeed listening.

Thanks for looking