Database Reference
In-Depth Information
Health Checks
Using JConsole to monitor your system is tedious and good as a monitoring sys-
tem only if you are actively staring at the graphs and information all the time.
Since that is unrealistic and time-consuming, we recommend that you use other
systems for monitoring the general health of your system such as Nagios.
Nagios
Nagios is open-source software dedicated to monitoring computers, networks,
hosts, and services and can alert you when things are going wrong or have been
resolved. It is extremely versatile and has the capability to monitor many types
of services, applications, or parts of an application. Let's start at the bottom of
the monitoring chain and work our way up. In order to avoid a complete lesson
on monitoring, we will only cover the basics along with what the most common
checks should be as they relate to Cassandra and its operation.
There are three primary alerts in Nagios:
WARNING
,
CRITICAL
, and
OK
. They
mean exactly what they sound like. A
WARNING
alert is sent if the service in ques-
tion is starting to show signs of a problem, such as a hard drive nearing capacity. A
CRITICAL
alert is sent if the service in question is down or in a catastrophic state,
such as a hard drive that is completely out of space and preventing the applications
using that drive from running. An
OK
alert is sent when the service has recovered
or become available again, such as when the total space used on the hard drive has
dropped below the threshold set to alert for
CRITICAL
or
WARNING
.
OS and Hardware Checks
When monitoring any machine, it's best to start out with the checks at the OS and
hardware layer. Even if you are running Cassandra in a virtualized environment
such as Amazon or Rackspace, there are still hardware(ish) checks that should be
instituted.
