Prometheus WebHook to SNMP-trap forwarder

This is a quick (and dirty) way to get Prometheus to send SNMP traps, by mapping AlertManager "Annotations" and "Labels" to generic SNMP OIDs.

Integration with Prometheus

1. Prometheus gathers metricscd
2. Prometheus appraises metrics against rules
3. If rules are triggered then alerts are raised through the AlertManager
4. The AlertManager triggers notifications to the webhook_snmptrapper
5. The webhook_snmptrapper forwards alerts as SNMP traps to the configured trap-address

SNMP integration

The traps are being send with the enterprise ID of .1.3.6.1.4.1.56.12.1.7 and the following specific IDs that designate alerts' severity levels:

Specific IDs:

• 0: normal/resolved
• 1: undetermined
• 2: warning
• 3: minor
• 4: major
• 5: critical

SNMP variables (as of version 0.0.9):

• Component: An instance or a hostname
• SubComponent: -- not populated yet --
• Severity: Alert's severity as set in prometheus rules configuration
• Message: Alert's text
• Summary: Alert's short description
• Namespace: Kuberneters namespace of the alerting component
• Application: Alert's prom_application as set in prometheus rules configuration
• Object: Alert's prom_object as set in prometheus rules configuration
• Datacenter: Alerting component's location by external_label

Command-line flags

• -snmpcommunity: The SNMP community string (default = public)
• -snmpretries: The number of times to retry sending traps (default = 1)
• -snmptrapaddress: The address to send traps to (default = 127.0.0.1:162)
• -webhookaddress: The address to listen for incoming webhooks on (default = 0.0.0.0:9099)

THE FOLLOWING IS NOT IN USE (legacy from chrusty/prometheus_webhook_snmptrapper):

The provided MIB (`PROMETHEUS-TRAPPER-MIB.txt`) defines two notifications:
- ***prometheusTrapperFiringNotification***: Notification for an alert that has occured
- ***prometheusTrapperRecoveryNotification***: Notification for an alert that has recovered

The MIB can be loaded into whatever SNMP Trap-server you're using. See [Dockerfile](trapdebug/net-snmp/Dockerfile) for a working demo using net-snmp on Alpine Linux.

### MIB's SNMP variables
Both of these traps contain the following variables:
- ***prometheusTrapperNotificationInstance***: The instance or hostname
- ***prometheusTrapperNotificationService***: A name for the service affected
- ***prometheusTrapperNotificationLocation***: The physical location where the alert was generated
- ***prometheusTrapperNotificationSeverity***: The severity of the alert
- ***prometheusTrapperNotificationDescription***: Text description of the alert
- ***prometheusTrapperNotificationTimestamp***: When the alert was first generated

---