I have an application listening on port 31515 on a sandbox RHEL server but I'm unable to access the same from my browser or telnet the port. I'm, however, able to access other ports (say port 80) without any issues.

The application (running on port 31515) is a Node JS application running inside a Kubernetes Cluster. The Kubernetes service made use of is NodePort and the port 31515 has been mentioned under nodePort parameter in the YAML file which was configured on the cluster using kubectl apply command.

Port 31515 and 80 listening as confirmed by the following netstat command:

[root@XYZ simplek8s]# netstat -anop | grep :31515
tcp6   0   0:::31515      :::*       LISTEN      20694/kube-proxy     off (0.00/0/0)
[root@XYZ etc]# netstat -anop | grep :80
tcp    0   0 0.0.0.0:80   0.0.0.0:*  LISTEN      31528/ncat           off (0.00/0/0)
tcp6   0   0 :::80        :::*       LISTEN      31528/ncat           off (0.00/0/0)

I have also turned off firewalld on my sandbox.

[root@XYZ etc]# service firewalld status
Redirecting to /bin/systemctl status firewalld.service
● firewalld.service - firewalld - dynamic firewall daemon
   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Sun 2020-02-16 06:01:35 EST; 5min ago
     Docs: man:firewalld(1)
  Process: 28342 ExecStart=/usr/sbin/firewalld --nofork --nopid $FIREWALLD_ARGS (code=exited, status=0/SUCCESS)
 Main PID: 28342 (code=exited, status=0/SUCCESS)

Telnet failure on port 31515:

C:\Users\vishwas>telnet <ServerIP> 31515
Connecting To <ServerIP>...Could not open connection to the host, on port 31515: Connect failed