Dear all,
We are interested in exploiting SNMP in general, and net-snmp in
particular, to monitor a dynamic cloud computing back-end that is
implemented by means of CloudStack [1]. The back-end consists of a
cluster of physical machines on which Virtual Machine (VM) instances are
spawned and destroyed on an as-needed basis. Each VM in turn is capable
of hosting multiple server applications, which are also dynamic in
nature in the sense that the number of server applications can fluctuate
over time. Combined, this yields a highly dynamic setup that is
characterized by both VM and application churn. The VMs currently run
Windows 7, yet might in the future be migrated to a Linux/Unix distribution.
We would like to monitor not only the spawned VMs globally, but also the
individual server applications which they accommodate. The monitoring
should in addition involve not only "physical" resource usage (i.e.,
CPU, memory, network bandwidth, ...), but also application-layer metrics
(e.g., number of clients that are connected to a particular application
server). Finally, we would like the monitoring to be automated as much
as possible. For example, as soon as a new VM is spawned, we would like
the NMS to automatically start collecting statistics about it; the same
holds true for situations where a new application server is started on
an existing VM. We are currently using Cacti [2] to aggregate the SNMP
data and to visualize the result.
Is it possible to realize this with net-snmp (and Cacti)? We have found
tutorials and documentation about how to extend the net-snmp agent to
support "non-standard" metrics. We have read about writing snmpd
extensions (e.g., [3]), and we have successfully experimented with the
"extends" directive to introduce new OID values (e.g., [4]). We
succeeded in using the latter approach to attach a "client_count" OID to
a local file on a VM's disk that is continuously updated with the
current client count of a server application that is running on that VM.
Unfortunately, we are struggling to generalize this approach so that it
works for dynamic numbers of application servers (and VMs).
From the information that we have collected so far, we feel like our
best bet is to define a custom MIB tree, with a branch for each of the
(physical or application-layer) metrics that we would like to monitor
from the application servers. For instance, the "client_count" branch of
the MIB tree could hold one instance/row for each currently active
application server to specify the current client count of this
particular server. Another branch could hold the CPU usage of each
application server. The NMS could then do a SNMP walk of these subtrees
to obtain, for example, the client count values of all currently running
application servers on a particular VM. Is this approach viable? If so,
how could it best be realized? If not, does any of you have any
suggestions about how our problem could be addressed?
Many thanks in advance!
Best regards,
Maarten Wijnants
[1] http://cloudstack.apache.org/
[2] http://www.cacti.net/
[3] http://www.net-snmp.org/wiki/index.php/TUT:Writing_a_MIB_Module
[4]
http://docs.fedoraproject.org/en-US/Fedora/16/html/System_Administrators_Guide/sect-System_Monitoring_Tools-Net-SNMP-Extending.html
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