NRPE vs. check_by_ssh

[Kevin Keane]

I think you are comparing apples and oranges here, because in most 
situations that I can think of, the decision is dictated by the network 
topology. If you are exclusively on a trusted private network, 
check_by_ssh really doesn't offer any benefits. Conversely, if your 
topology involves the Internet or some other untrusted network (WiFi), 
then you wouldn't want NRPE in the first place.

The only exception to the above that I can think of is when it comes to 
deciding between using check_by_ssh over an untrusted network, vs. NRPE 
through some other kind of tunnel or VPN. But in that case, you'd incur 
encryption overhead either way, and the comparison is very different 
from the question you asked.

All that said: I don't have any first-hand experience, but I suspect 
that the impact of establishing 2200 ssh connections in a five-minute 
span (assuming that you are using a five-minute check interval) is 
pretty substantial. The main impact actually lies in establishing and 
tearing down the connections, key negotiations etc.; the encryption 
during the data phase probably has only limited impact because most 
checks only transmit a few bytes back and forth.

SSH does much better with longer-duration connections when the keys are 
already exchanged. This is even more true if you have a router-based 
VPN, because in that case the overhead is offloaded to a different machine.

So if you have the option of sending the checks as NRPE through one or a 
few long-term VPNs: you are probably going to be better off. Of course, 
in the big picture, your mileage may vary.

Christopher McAtackney wrote:
> Hi all,
>
> I was wondering if someone could give a brief overview of the pros /
> cons of using NRPE to monitor my remote hosts versus using the
> check_by_ssh command?
>
> I'm aware that check_by_ssh increases the CPU overhead, but I'm not
> clear on the level of impact here - does this increase the load on the
> monitoring machine in direction relation to the number of hosts being
> monitored? For example, if I was using check_by_ssh to monitor, say,
> 2000 services spread across 200 hosts, would I experience significant
> slowdown on my monitoring machine?
>
> Cheers for any info,
>
> Chris
>   


-- 
Kevin Keane
Owner
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