# edit /usr/local/nagios/etc/nrpe.cfg
command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10

command[check_load]=/usr/local/nagios/libexec/check_load -w 15,10,5 -c 30,25,20

command[check_hda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/hda1
[-- snip --]
#custom commands *add your commands here*

# EC2 ephemeral storage root disk
command[check_sda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/sda1

# A machine to be monitored
# DEFINE ALL CASSANDRA HOSTS HERE

define host{
        use                     linux-server
        host_name               cassandra1
        alias                   Cassandra Machine
        address                 10.99.9.67
        }

# create logical groupings, manageable, saves typing
# HOST GROUP TO COLLECTIVELY CALL ALL CASSANDRA HOSTS

define hostgroup{
        hostgroup_name  cassandra_grp
        alias           Cassandra Group
        members         cassandra1  ;this is CSV of
                                    ;hosts defined above
        }

# A service defines what command to execute on what hosts
# MONITORING SERVICES

# A service that executes locally
#Check Cassandra on remote machines

define service{
        use                     generic-service
        hostgroup_name          cassandra_grp
        service_description     Cassandra
        check_command           check_cas ;defined below
        }

# A service that gets executed remotely via NRPE
# check disk space status
define service{
  use                 generic-service
  hostgroup_name      cassandra_grp
  service_description check disk
  check_command       check_nrpe!check_sda1
  }

# check CPU status
define service{
  use                 generic-service
  hostgroup_name      cassandra_grp
  service_description check CPU
  check_command       check_nrpe!check_load
  }

# A command is a template of a command line call, here:
#   $USER1$ is plugin directory, nagios/libexec
#   $HOSTADRRESS$ resolves to the address defined in
#   the preceding host block; hosts are chosen from the service that calls this command

# define custom commands
# check JVM heap usage using JMX,
# warn if > 3.7G, mark critical if > 3.85G

define command {
        command_name check_cas
        command_line $USER1$/check_jmx -U service:jmx:rmi:///jndi/rmi://$HOSTADDRESS$:7199/jmxrmi -O java.lang:type=Memory -A HeapMemoryUsage -K used -I HeapMemoryUsage -J used -vvvv -w 3700000000 -c 3850000000
        }

#custom file *ADD YOUR FILES HERE*
cfg_file=/usr/local/nagios/etc/objects/cassandrahosts.cfg
Test the configuration and you are done.
$ sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
Nagios Core 3.5.0
[-- snip --]
Reading configuration data...
   Read main config file okay...
Processing object config file '/usr/local/nagios/etc/objects/commands.cfg'...
Processing object config file '/usr/local/nagios/etc/objects/contacts.cfg'...
Processing object config file '/usr/local/nagios/etc/objects/timeperiods.cfg'...
Processing object config file '/usr/local/nagios/etc/objects/templates.cfg'...
Processing object config file '/usr/local/nagios/etc/objects/cassandrahosts.cfg'...
Processing object config file '/usr/local/nagios/etc/objects/localhost.cfg'...
   Read object config files okay...
Running pre-flight check on configuration data...
[-- snip --]
 Total Warnings: 0
Total Errors:   0
Things look okay - No serious problems were detected during the pre-flight check