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Ubuntu Linux 14.04 LTS - SNMPD Configuration with Baracuda Load Balancer

posted 18 Feb 2015, 06:55 by Tristan Self   [ updated 19 Mar 2015, 09:48 ]
We have some Linux web servers that we use for Moodle they are setup behind a Barracuda Load Balancer that then distributes the load based on how busy each of the web servers are. Essentially the more busy the server the less clients it is given to process. The barracuda load balancer uses an SNMP query determining the current load.

The Barracuda load balancer side is well documented, but the configuration on your Linux box is not so much, so assuming you've configured the Barracuda you just need to follow these steps on the 14.04 LTS Ubuntu server. Remember this is a basic configuration, offering basic security, so if you are looking to do this you need to review these settings, but this gives a basic operational configuration.

Firstly install SNMPD (the SNMP agent) that can respond to SNMP queries:
apt-get install snmpd (Install the SNMP listener)

Now download the SNMP MIBS, these are not included in the SNMP package anymore you need to get them separately with this.
apt-get install snmp-mibs-downloader

Once this is done you need to replace the /etc/snmp/snmpd.conf file with the following, this will allow you to access this SNMP agent from any host on the 192.168.0.0/24 network using the community string: "mycommunitystring."

###############################################################################
#
#  AGENT BEHAVIOUR
#
###############################################################################

#  Listen for connections from all IPv4 addresses on the network
agentAddress udp:161

###############################################################################
#
#  ACCESS CONTROL
#
###############################################################################

view   systemonly  included   .1.3.6.1.2.1.1
view   systemonly  included   .1.3.6.1.2.1.25.1

#rocommunity communitystring  default    -V systemonly
rocommunity mycommunitystring 192.168.0.0/24

rouser   authOnlyUser

###############################################################################
#
#  SYSTEM INFORMATION
#
###############################################################################

sysLocation    Place
sysContact     Things servicedesk@somewhere.com

sysServices    72

proc  mountd
proc  ntalkd    4
proc  sendmail 10 1

disk       /     10000
disk       /var  5%
includeAllDisks  10%

load   12 10 5

###############################################################################
#
#  ACTIVE MONITORING
#
###############################################################################

trapsink     localhost public
iquerySecName   internalUser
rouser          internalUser
defaultMonitors          yes
linkUpDownNotifications  yes

###############################################################################
#
#  EXTENDING THE AGENT
#
###############################################################################

extend    test1   /bin/echo  Hello, world!
extend-sh test2   echo Hello, world! ; echo Hi there ; exit 35

master          agentx


To get the SNMPD daemon to take the setting restart it:

service snmpd restart


Now from another Linux box you should be able to get the CPU load back using SNMPWalk to test with:

snmpwalk -v1 -c mycommunitystring myhost.domain.com 1.3.6.1.4.1.2021.10.1.3.1


If it works you should see something like: UCD-SNMP-MIB::laLoad.1 = STRING: 0.04

Now using the Test button on the Barracuda Load Balancer configuration, you can test the SNMP load balancing you should see it calculating a metric based on the current load of the server.

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