Votes: 0Posted On: Oct 13, 2017 05:45:29
Nagios is considered to be one of the top server monitoring tools that offer a variety of different ways. It is flexible as it can monitor your server with and without agents.
The community at Nagios has done a great job by making different addons available for server monitoring.
When it comes to mission-critical infrastructure, Nagios proves to be a powerful tool that gives you all the information you need time to time.
So how does it work?
Nagios basically collects the statistics of your server (either using agent like nrpe, check_mk or via snmp ) and send the alert to you if the value of the metric is above some predefined threshold.
Nagios after every interval checks the status of a remote service by executing a plugin, that will be placed on the remote client.
We'll discuss some of the techniques Nagios uses for monitoring in the following description.
Nagios Remote Plugin Executor (NRPE)
Nagios installs this package on all the remote hosts that need to be monitored and it communicates on the tcp port 5666.
The NRPE holds a configuration file where all the commands need to be defined. So whenever Nagios server raises a query which is received by the NRPE daemon, it looks for the desired command inside the config file and accordingly executes it.
Monitoring using SNMP
The main advantage of using SNMP is that it is supported by a wide variety of devices including routers, switches and UPS devices.
With the help of SNMP, you can monitor the network, OS as well as hardware by simply installing it daemon on the remote host. This is possible since SNMP can fetch values of different properties of network devices or any other device that is aware of SNMP.
NSCA - Nagios Service Check Acceptor
Here the client will execute a required plugin at his end in regular intervals and report the output to the Nagios server.
This type of monitoring is also called passive monitoring because Nagios server is not responsible for initiating checks but the client will execute plugins at regular intervals and report it back to NSCA on Nagios server.