This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Jiafan Zhou wrote:
One way I can image is to monitor the CPU usage of such component or the memory footprint. Is that correct?
Yes. We also monitor ping (to make sure the network and hardware are up), HTTP (to make sure the server's responding) and response time (to make sure it's not overwhelmed). We also have some pages that our monitors scan for a particular piece of text that has to be recovered from the database, so we can be sure our application stack is working.
We use a combination of Nagios and ipMonitor (ipMonitor has more tools to monitor Windows machines) which send alerts via email, pager and SMS.