What does server monitoring software do?
Network Monitors constantly monitors a computer network for slow
or failing components and that notifies the network administrator
(via email, pager or other alarms) in case of outages. It is a
subset of the functions involved in network management.
While an intrusion detection system monitors a network for
threats from the outside, a network monitoring system monitors the
network for problems caused by overloaded and/or crashed servers,
network connections or other devices.
For example, to determine the status of a webserver, monitoring
software may periodically send an HTTP request to fetch a page. For
email servers, a test message might be sent through SMTP and
retrieved by IMAP or POP3.
Commonly measured metrics are response time, availability and
uptime, although both consistency and reliability metrics are
starting to gain popularity. The widespread addition of WAN
optimizationdevices is having an adverse effect on most network
monitoring tools -- especially when it comes to measuring accurate
end-to-end response time because they limit round trip
visibility.
Status request failures - such as when a connection cannot be
established, it times-out, or the document or message cannot be
retrieved - usually produce an action from the monitoring system.
These actions vary -- an alarm may be sent (via SMS, email, etc.)
to the resident sysadmin, automatic failover systems may be
activated to remove the troubled server from duty until it can be
repaired, etc.
Monitoring the performance of a network uplink is also known as
network traffic measurement, and more software is listed there.