Tuesday, 1 December 2015

Extending SNMP

One of the things I love about SNMP is how easy it is to extend and use it as a wrapper service.

I was training some of my colleagues today on SNMP and as part of the course we covered extending SNMP in detail.

Beyond the simple things like echoing back a value, it's great that it can call external scripts and pass arguments to them.

An example of this is to be able to get the percentage of used disk space on a hard drive.
To extend snmp, we add a line to snmpd.conf file.
extend rootspace /bin/bash /scripts/getdiskspace.sh /dev/disk1

/scripts/getdiskspace.sh - the script to call

/dev/disk1 - the parameter to pass to the script.

Once we have set this up, we can get all of the extended parameters by walking the NET-SNMP-EXTEND-MIB::nsExtendObjects OID

snmpwalk -c public NET-SNMP-EXTEND-MIB::nsExtendObjects

Which gives us:
NET-SNMP-EXTEND-MIB::nsExtendNumEntries.0 = INTEGER: 2
NET-SNMP-EXTEND-MIB::nsExtendCommand."dataspace" = STRING: /bin/bash
NET-SNMP-EXTEND-MIB::nsExtendCommand."rootspace" = STRING: /bin/bash
NET-SNMP-EXTEND-MIB::nsExtendArgs."dataspace" = STRING: /scripts/getdiskspace.sh /Volumes/Data
NET-SNMP-EXTEND-MIB::nsExtendArgs."rootspace" = STRING: /scripts/getdiskspace.sh /dev/disk1
NET-SNMP-EXTEND-MIB::nsExtendInput."dataspace" = STRING: NET-SNMP-EXTEND-MIB::nsExtendInput."rootspace" = STRING: NET-SNMP-EXTEND-MIB::nsExtendCacheTime."dataspace" = INTEGER: 5
NET-SNMP-EXTEND-MIB::nsExtendCacheTime."rootspace" = INTEGER: 5
NET-SNMP-EXTEND-MIB::nsExtendExecType."dataspace" = INTEGER: exec(1)
NET-SNMP-EXTEND-MIB::nsExtendExecType."rootspace" = INTEGER: exec(1)
NET-SNMP-EXTEND-MIB::nsExtendRunType."dataspace" = INTEGER: run-on-read(1)
NET-SNMP-EXTEND-MIB::nsExtendRunType."rootspace" = INTEGER: run-on-read(1)
NET-SNMP-EXTEND-MIB::nsExtendStorage."dataspace" = INTEGER: permanent(4)
NET-SNMP-EXTEND-MIB::nsExtendStorage."rootspace" = INTEGER: permanent(4)
NET-SNMP-EXTEND-MIB::nsExtendStatus."dataspace" = INTEGER: active(1)
NET-SNMP-EXTEND-MIB::nsExtendStatus."rootspace" = INTEGER: active(1)
NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."dataspace" = STRING: 93
NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."rootspace" = STRING: 76
NET-SNMP-EXTEND-MIB::nsExtendOutputFull."dataspace" = STRING: 93
NET-SNMP-EXTEND-MIB::nsExtendOutputFull."rootspace" = STRING: 76
NET-SNMP-EXTEND-MIB::nsExtendOutNumLines."dataspace" = INTEGER: 1
NET-SNMP-EXTEND-MIB::nsExtendOutNumLines."rootspace" = INTEGER: 1
NET-SNMP-EXTEND-MIB::nsExtendResult."dataspace" = INTEGER: 0
NET-SNMP-EXTEND-MIB::nsExtendResult."rootspace" = INTEGER: 0
NET-SNMP-EXTEND-MIB::nsExtendOutLine."dataspace".1 = STRING: 93
NET-SNMP-EXTEND-MIB::nsExtendOutLine."rootspace".1 = STRING: 76

The info we are interested in are the output lines:

NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."rootspace" = STRING: 93
NET-SNMP-EXTEND-MIB::nsExtendOutLine."rootspace".1 = STRING: 93

The result value gives the exit status of the script, so we could pass an integer on exit to this parameter

NET-SNMP-EXTEND-MIB::nsExtendResult."rootspace" = INTEGER: 0

To get just a single response with snmpget, we would use the following:

snmpget -c public 'NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."rootspace"'
which responds with:

NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."rootspace" = STRING: 76

This format of the above line is:
extend - the extend directive
rootspace - the extension command that the daemon will respond to
/bin/bash - the external environment to run the extension in

Sunday, 29 November 2015

Thoughts on the future of IT

I have just become a certified AWS Solutions Architect, and along the journey to becoming qualified a new perspective regarding the future of IT for the SMB market is slowly dawning on me.

In the past the standard procedure was to put kit on premise, and then to maintain it as hosting it / paying a provider was quite often more expensive.

Now however the market is changing and it no longer makes sense to put kit on premise due to the economies of scale and high resilience offered by hosting services such as AWS.

Couple this with the decreasing cost of internet connectivity, and the move to truly cloud based infrastructure makes sense.

I am currently designing HA systems that have little to no on premise infrastructure, with almost everything provided as a managed service.

This moves most of the cost into OP-EX, and reduces the TCO drastically, and seems to be a no brainer!