We are planning to monitor Server status for few critical servers and generate an alarm if the server is not up/pinging.
From availability and reachability, which one is better to use to measure the server status? Please suggest.
Reachability is a response to ping.
eHealth calculates Reachability as "the percentage of time eHealth can communicate with an element or the device on which it resides".
Availability is response to snmp-get request.
Also for cisco network devices, it considers the uptime of the device.
Availability measures the percentage of time that an element is active and running.
eHealth calculates availability for each element type except modem pools.
More details at:
How does eHealth calculate availability
Reachability is the ping response from the eHealth poller assuming ping is enabled. So from live exception point, if the target server is not reachable either because it is down or due to some network glitch, then reachability is what you could use.
I agree with Pothen and Alex. Reachability is based on ping and availability is based on sysup OID .
Refer to Tuesday Tip: Best Practice to get alarms for Down devices
Best Practice to get alarms for Down devices
Do you notice that Availability alarms do not appear in Live Exceptions when a device goes down?What is the difference between a Reachability alarm and an Availability alarm in Live Exceptions?How does an Availability alarm differ from a Reachability alarm?
Here's the reasoning and the best practice.
Availability is the measure of whether or not a device is operational.
If eHealth is not able to communicate with a device, this is not necessarily a true indication that the device is non operational as the lack of communication could be due to a problem with the network, or with a Router or Switch between eHealth and the device, for example.
Once eHealth has reestablished contact and can successfully poll the device, we can determine whether or not the device was operational during the time period that communication was down. Because of this, Availability alarms will not appear in the Live Exceptions browser until after we have reestablished communication with the device.
A Reachability rule can be used to create alarms that appear as soon as eHealth is unable to successfully ping the target device. While Availability alarms will only appear after we can determine that the device was down, the Reachability alarms will appear as soon as eHealth's ping attempts to a device fail.
Hope that helps.
Thank you All for your valuable inputs.