How Do You Troubleshoot HAProxy when The Service Seems to Work on The Back-end but You Cannot Use It from The Front-end (via a web browser)?

Problem scenario
Your HAProxy server seems to be up, but it is not working.  You use nmap or a PowerShell port testing program (see "Using PowerShell Version 3, How Do You Determine If a Port Is Open for a given IP Address?").  You find that there is activity on port 80 and/or the traffic is not blocked over port 80.  But when you open a web browser, you get "File not found" or "The site cannot be reached."  What do you need to do?

Possible Solution #1
Start the HAProxy service (if it was not already started).  Use this command: sudo /etc/init.d/haproxy restart

Possible Solution #2
Is traffic blocked from your HAProxy server?  Verify you have connectivity from your HAProxy server to your webserver(s).  The port is determined in the haproxy.cfg file (e.g., 5001 or 80). 

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