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Alertmanager Event Handler

Use Prometheus' Alertmanager to handle arbitrary events. Inspired by the event handlers in Nagios.

This works as a generic web hook in Alertmanager. Alerts routed to this event handler must have an annotation handler defined who's value is the event handler that should be executed. Optionally, the annotation handler value may include arbitrary arguments passed to the event handler.

<handler> [arg1, [arg2 ...]]

The configuration file for am-event-handler contains a hash of known handlers which maps to a Go templated string. This string builds the executable and arguments that will run as the user running am-event-handler. This allows the passing of arbitrary data with reasonable security restrictions in place. Example:

ALERT PrometheusInstanceDown
  IF up{job="prometheus", environment="prod"} == 0
  FOR 5m
  LABELS {
    severity="event"
  }
  ANNOTATIONS {
    summary="{{$labels.instance}} Prometheus Instance Down",
    description="The Prometheus Instance {{$labels.instance}} is down",
    runbook="https://wiki/prometheus-instance-down",
    handler="restart-prom {{$labels.instance}}"
  }

This alert would be routed to event handler receiver in the Alertmanager by the severity label. The receiver configuration might look like the below:

# A list of notification receivers.
receivers:
  - name: foobar
    webhook_configs:
      - url: http://host:port/

Where the host:port is where am-event-handler is running.

The am-event-handler requires a configuration file that will map the handlers into an executable. These are not run through a shell and shell redirection will not work, but you can use this to execute a shell. The following is an example configuration:

handlers:
  restart-prom: "remctl {{ index .Argv 0 }} prom-restart"

Note that the supplied arguments are stored in the Argv slice of strings.

Meta Handlers

Handlers are defined in the configuration file and can be any arbitrary, non-whitespace containing string. The handler selected matches the first word of the handler annotation exactly. There is no fancy logic there.

However, there are two meta handlers that can be defined in the configuration that affect what will be executed.

  • default: A handler of this name will be executed when no handler annotation is present, or the requested handler cannot be found.
  • all: This handler is run for all alerts whether they have a handler annotation or not. It will be run in addition to (and after) any matching handler the alert requests.

Templating

In the configuration file the command to be executed can be templated as in the example above. In addition to Go's built in text template functionality the following are made available.

Variables:

  • .Status: string The status of the alert. This should be either "firing" or "resolved".
  • .Labels: map[string]string A map of the labels applied to this alert.
  • .Annotations: map[string]string A map of the annotations applied to this alert.
  • .StartsAt: string The RFC 3339 date the alert began as from the Alertmanager.
  • .EndsAt: string The RFC 3339 date the alert ended as from the Alertmanager. May be "0001-01-01T00:00:00Z" when the alert is in progress.
  • .GeneratorURL: string The URL to the originating Prometheus server and graph.
  • .Argv: []string A slice of strings holding the arguments present in the handler annotation. The handler annotation is whitespace delimited and this slice begins at the first argument and does not include the name of the specified handler.
  • .Json: string A JSON representation of this alert. This is a filtered representation of the alert and not the complete JSON as provided by the Alertmanager.
  • .Timestamp: string A UTC timestamp in RFC 3339 format of when Alertmanager hit the am-event-handler with this alert.

Functions:

  • replace <string> <substring> <replacement>: This allows simple replacement based substitution of strings. Perhaps dealing with escaping some pesky quotes. As the templates are specified in YAML there is YAML escaping done on top of the Go string escaping before the string is parsed as a template.

Contributing

Clone this repository and create a GitHub PR.

Authors and Copyright

Copyright 2016 - 2017 42 Lines, Inc. Original author: Jack Neely jjneely@42lines.net