Simply copy paste the script uptimemonitor.py into your server. After you test it add it to cron with your preferred check interval

Example for checks every minute

$crontab -e
* * * * * /home/uptimemonitor/uptimemonitor.py > /root/uptimenotifier.log
$service cron restart
$tail -f /root/uptimenotifier.log

Note that the script is written in Python3.5.

URLS_TO_CHECK = ["http://facebook.com", "https://youtube.com:9540"]

https://api.slack.com/docs/oauth-test-tokens

You need then to export it as an environmental variable or hardcoded

export SLACK_TOKEN = 'your_token_here'

SLACK_TOKEN = os.environ.get('SLACK_TOKEN')

you can get it using list_channels and channel_info or click on the channel name

click on add app or integration and you can view it's id in the webpage redirection (you have to be fast because it redirects it to another page)

CHANNEL_ID = "G2LCBCXGF"