Unable to establish connection using ssh2_connect() in PHP

I have used the ssh2_connect() function to establish a connection to a remote SSH server. But it works on one webserver and fails on another (let’s call it as webserver1 and webserver 2 hereafter).  I get this error – unable to establish connection error on webserver2. Both the webservers 1 & 2 are identical setups running Apache and what’s is strange is that the issue occured only after the reboot of the webserver2. The complete apache error_log of webserver2 is as follows:

[Wed Dec 15 10:30:35 2021] [error] [client 192.168.xxx.xx] PHP Warning:  ssh2_connect(): Unable to connect to 192.168.xx.xxx on port 22 in /var/www/html/process.php on line 9
[Wed Dec 15 10:30:35 2021] [error] [client 192.168.xxx.xx] PHP Warning:  ssh2_connect(): Unable to connect to 192.168.xx.xxx in /var/www/html/process.php on line 9

Below is the PHP-script:

if (!function_exists("ssh2_connect")) die("function ssh2_connect doesn't exist");
     if(!($con = ssh2_connect(REMOTE_IP, 22))){
           echo "fail: unable to establish connection\n";
     } else  {
          // try to authenticate with username root, password secretpassword
          if(!ssh2_auth_password($con, $username, $password)) {
                 echo "fail: unable to authenticate\n";
                 header('Location: ../../login/?error=1');
                 exit();
           } else {
                 echo "Logged in..\n";
           }
     }

How to solve ssh_connect() : unable to establish connection

Step 1: Check for the firewall on the remote server. A firewall rule might be blocking the connections from webserver2.

Step 2: Lets test the SSH from terminal of webserver2 as below:

# ssh <username>@<REMOTE_IP> -p 22

Step 3: If the above SSH command works, then check if SELinux is enabled. If enabled, make sure to bypass SELinux for web directories as it might be blocking.

Step 4: By default, SELinux prevents Apache web server from establishing network connections.

Run the below command to allow HTTPD scripts and modules to connect to the network using any TCP port.

#  /usr/sbin/setsebool -P httpd_can_network_connect 1

That’s it!