[hobbit] Agentless clients

Charles Jones jonescr at cisco.com
Thu Jan 5 17:21:15 CET 2006

Daniel J McDonald wrote:

>But having one or two servers that poll all of the others does scale
>well, because you don't have to install (and upgrade) hobbit clients on
>a hundred machines - just set up an rsa key and you are done.  If the
>primary hobbit display/alarm/parse work is too much with the polling
>added, just use a second hobbit server for polling/parsing and feed the
>results to the display server...
I disagree. The distributed system scales much better, as the remote 
servers are sending in their results in parallel.
While fping is able to test remote hosts in parallel, the other test are 
done in serial (bb-fetch, etc).

Lets say you have 1000 hosts. Lets then just for fun pretend that it 
will only take 1 second to log into the remote hosts, run several tests, 
and receive the result (it would actually take a bit longer than that).

1000 seconds (hosts) / 60 (minutes) = 16.666 minutes to poll those hosts!

So then you can say oh well just have 2-3 hobbit servers doing the 
polling then.  Now you have 3 hobbit servers to deail with, monitoring 
them, upgrading them, etc.

Now lets look at a *real world* example of how long it takes to ssh in 
and execute a command:

[hobbit at hobbit ~]$ time ssh myhost.net df -h
Filesystem             size   used  avail capacity  Mounted on
/dev/dsk/c5t0d0s0       30G    10G    20G    35%    /
/devices                 0K     0K     0K     0%    /devices
ctfs                     0K     0K     0K     0%    /system/contract
proc                     0K     0K     0K     0%    /proc
mnttab                   0K     0K     0K     0%    /etc/mnttab
swap                   6.6G  1000K   6.6G     1%    /etc/svc/volatile
objfs                    0K     0K     0K     0%    /system/object
fd                       0K     0K     0K     0%    /dev/fd
swap                   6.6G    16K   6.6G     1%    /tmp
swap                   6.6G    32K   6.6G     1%    /var/run
/dev/md/dsk/d0         639G   116G   523G    19%    /raid
/dev/md/dsk/d1         807G   504G   304G    63%    /raid2

*real    0m1.912s*
user    0m0.022s
sys     0m0.008s

Almost 2 seconds there....and just for one command. So now even 2 hobbit 
servers polling simultaneously will still take over 15 minutes just to 
poll 1000 servers. Having hobbit do the ssh's in parallel wouldn't work 
either, I have tried something similar on far fewer hosts, and even 
using -c blowfish option the server CPU still hit 100% from all the 

The way that I get around this is to have bbproxy running on a DMZ host, 
and have the hobbit/bb clients configured to use the bbproxy IP as their 
BBDISPLAY, whcih then forwards the traffic out of the DMZ to my hobbit 
server.  Not 100% secure, but using bb-fetch isn't either (an attacker 
could compromise one of the remote servers, and modify one of the 
commands that the hobbit user executes, thus giving them the ability to 
communicate with the hobbit server, injecting something to break the 
parsing engine, buffer overflows, etc). I will stop talking about that 
now as I am getting off subject :)

I agree that having similar functionality to bb-fetch could be useful 
for a *few* remote/DMZ hosts, but it certainly doesn't scale well. Once 
you reach a number of hosts whose polling time exceeds the hobbit 
refresh interval you are done.  I know it would be "nice" if we didn't 
have to upgrade remote clients and maintain them, but your solution 
involves ssh keys, so just use those same keys and a script to roll out 
the updates :)

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