Uly.me

cloud engineer

Internet Test

My internet has been flaky lately. I wrote a script that logs my internet connection.

I’m running it in cron every minute.

#!/bin/bash
log='/home/ulysses/Code/spectrum.log'
if nc -zw1 google.com 443;
then 
  echo 'Spectrum is up' $(date) >> $log
else 
  echo 'Spectrum is down' $(date) >> $log
fi

To view, just cat the log.

cat spectrum.log 
Spectrum is up Fri Jun 26 15:14:01 EDT 2020
Spectrum is up Fri Jun 26 15:15:01 EDT 2020
Spectrum is up Fri Jun 26 15:16:01 EDT 2020
Spectrum is up Fri Jun 26 15:17:01 EDT 2020
Spectrum is up Fri Jun 26 15:18:01 EDT 2020

So, I now have a record when it was up or down.

Testing a Network Port Connection

You can test a network port connection using the “nc” command on Linux and “telnet” on Windows.

Format:
$ nc -zv domain.com port
C:\> telnet domain.com port

$ nc -zv domain.com 80
Connection to domain.com 80 port [tcp/http] succeeded!
C:\> telnet -zv domain.com 80
Connecting To domain.com...Could not open connection to the host, on port 80: Connect failed

For Telnet, if a connection is successful, it returns no message.

Check DB Connection on AWS

When setting up your cloud infrastructure, you can check if your instances have access to the database by performing this command.

$ nc -zv 10.0.0.45 3306
$ nc -zv domain.com 3306
$ nc -zv endpoint.amazonaws.com 3306

If connection has succeeded, you’ll get a message like this in Linux and MacOS …

Connection to endpoint.amazonaws.com 3306 port [tcp/mysql] succeeded!

On Windows, you can use Telnet to test your DB connection.

C:\>telnet endpoint.amazonaws.com 3306

If connection has succeeded, the result is “no message.” If there’s a problem, you’ll get this ….

Connecting To endpoint.amazonaws.com...Could not open 
connection to the host, on port 3306: Connect failed