A sensu mutator to add EC2 instance's tags to event data

ec2_tags.rb

#!/usr/bin/env ruby

require 'json'
require 'aws-sdk-core'

module Sensu::Extension
  class EC2Tags < Mutator
    def name
      'ec2_tags'
    end

    def description
      'Add EC2 instance\'s tags'
    end

    def post_init
      @aws_region = settings['aws']['region']
    end

    def run(event)
      mutated = 
        if event[:client][:name] =~ /^i-[0-9a-z]+/i
          # If the client is EC2 instance, fetch its tags and add those to the event json
          resp = Aws::EC2::Client.new(region: @aws_region).describe_instances({instance_ids: [event[:client][:name]]})
          instances = resp.reservations.map { |r| r.instances }.flatten

          if instances.length > 0
            tags = instances.first.tags.reduce({}) { |a, b| a.merge({ b.key => b.value }) } # => e.g. { 'Name' => 'prd-example-web', 'Role' => ... }
            event.merge(client: {ec2: {tags: tags}})
          else
            event
          end
        else
          event
        end

      yield(JSON.dump(mutated), 0)
    end
  end
end

/sensu/extensions/mutators/ec2_tags.rb

{
  "handlers": {
    "pagerduty": {
      "type": "pipe",
      "command": "/etc/sensu/handlers/pagerduty.rb",
      "mutator": "ec2_tags"
    },
...