prometheus-snmp-exporter

Published on Mar 25, 2022 by Kristian Alexander P.

I need to write this down before I forgot.

Setting up prometheus’s snmp-exporter isn’t as straight-forward as many blogs and tutorial on the internet. Mostly those articles only covers the installation part, without diving much to the snmp side of things. So here’s what I think is the important part.

Make sure you have a running snmpd daemon snmp

And verify it, even better, run snmpwalk from another remote machine to also making sure there’s no firewall issues. If snmp and snmp exporter is in the same machine, I suppose it’s safe to use snmp version 1 or 2c. There’s already too much documentations on snmp (on arch, there’s a net-snmp package in the repository). As far as snmp side, this is basically it.

snmp-exporter

This is where I got lost initially. From their official github repo readme, the example config looks like this:

scrape_configs:
- job_name: 'snmp'
  static_configs:
    - targets:
      - 192.168.1.2  # SNMP device.
      - switch.local # SNMP device.
  metrics_path: /snmp
  params:
    module: [if_mib]
  relabel_configs:
    - source_labels: [__address__]
      target_label: __param_target
    - source_labels: [__param_target]
      target_label: instance
    - target_label: __address__
      replacement: 127.0.0.1:9116  # The SNMP exporter's real hostname:port.

This is assuming if-mib is sufficient. Unfortunately, I needed more MIB’s. Since prometheus-snmp-exporter is an AUR package, it’s not in the wiki. There’s a readme file though, especially for the generator because this is what I’m looking for. In archlinux the generator binary is in /usr/bin/prometheus-snmp-generator. What’s left is the generator.yml file, there’s a sample config file in the generator readme. But for someone not familiar with snmp like me this is too vague. Luckily there’s another sample configuration file in their github repo. I removed all that I don’t use and eventually left with this:

modules:
  # Default IF-MIB interfaces table with ifIndex.
  if_mib:
    walk: [sysUpTime, interfaces, ifXTable]
    lookups:
      - source_indexes: [ifIndex]
	lookup: ifAlias
      - source_indexes: [ifIndex]
	# Uis OID to avoid conflict with PaloAlto PAN-COMMON-MIB.
	lookup: 1.3.6.1.2.1.2.2.1.2 # ifDescr
      - source_indexes: [ifIndex]
	# Use OID to avoid conflict with Netscaler NS-ROOT-MIB.
	lookup: 1.3.6.1.2.1.31.1.1.1.1 # ifName
    overrides:
      ifAlias:
	ignore: true # Lookup metric
      ifDescr:
	ignore: true # Lookup metric
      ifName:
	ignore: true # Lookup metric
      ifType:
	type: EnumAsInfo

Save this as generator.yml and run prometheus-snmp-generator generate in the same directory, and you’ll get the snmp.yml. This is still not enough for me since what I’m looking for is actually in the IP-MIB OID. I could manually list all the OID’s, but that’ll take a while, a quick google search and I got this. And I modify the generator.yml file:

modules:
  if_mib:
    walk:
      - interfaces
      - sysUpTime
      - ifXTable
      - 1.3.6.1.2.1.4
      - 1.3.6.1.2.1.55
    lookups:
      - source_indexes: [ifIndex]
	lookup: ifAlias
      - source_indexes: [ifIndex]
	lookup: 1.3.6.1.2.1.2.2.1.2 # ifDescr
      - source_indexes: [ifIndex]
	lookup: 1.3.6.1.2.1.31.1.1.1.1 # ifName
    overrides:
      ifAlias:
	ignore: true # Lookup metric
      ifDescr:
	ignore: true # Lookup metric
      ifName:
	ignore: true # Lookup metric
      ifType:
	type: EnumAsInfo
    auth:
      community: ro_java281

The additional walk is for IP-MIB and IPV6-MIB, on arch it’s available at /usr/share/snmp/mibs (provided you’ve installed net-snmp).