This simple script uses
netcat to check if - for instance - a webserver is running on a server. If the service is not running, it utilizes the telegram bot API for sending a message to inform the operator of the server.
Go to the BotFather bot-account and create a bot by writing
/newbot. Then, copy the token.
Send a message to you newly created bot (you can find the link to your bot in the success message sent by BotFather).