Nagios Plugins: Run Existing Checks & Custom Scripts

A lot of teams have a collection of Nagios plugins and custom monitoring scripts that have been running reliably for years. Some are standard community plugins for checking disk health or SSL certificate expiry. Others are homegrown Bash or Python scripts that check something very specific to the business: whether an API endpoint returns the right payload, whether a batch job completed on time, whether a queue depth is within bounds.