How to trouble shoot when you get a "Connection refused" when accessing an application running on a different server (centOS / RHELs)

Say you are trying to connect to server running on a remote machine you get a connection refused.

EX: Error massage says connection refused when trying to connect to https://192.168.1.1:8090/server/home

One of the reasons for this error can be your remote machine doesn't allow other IPs to connect through the particular port. In other words the the port which your trying connect is closed.  To check that

1. Ping to the particular IP

Ex : In the terminal you can run
ping 192.168.1.1

If it is successful;

2. Telnet and see whether you can connect to the port

Ex: telnet 192.168.1.1 8090

3. If you get a connection refused for above command then try below command.

sudo iptables -F INPUT

** Above command flushes all rules and open all ports for the logged it session.

4. Then when you telnet to the port and if you successfully get connected with the port the issue is the particular port is closed.

5. To open the particular port you need to add it to /etc/sysconfig/iptables.

EX: -A INPUT -m state --state NEW -m tcp -p tcp --dport 8090 -j ACCEPT

Note : When adding make sure you add it before REJECT rules.

6.  After adding you run

sudo service iptables restart

Now you have opened the particular port and other machine should be successfully connect using that port.