Report Phusion Passenger metrics to AWS CloudWatch.

report-passenger.rb

#!/usr/bin/env ruby
#
# Report Instance Count and Request Queue Size metrics from locally running Phusion Passenger instance.
# Author: Andrew Page <andrew@andrewpage.me>
# ==
# Phusion Passenger: https://www.phusionpassenger.com

require 'net/http'
require 'phusion_passenger'
require 'aws-sdk-cloudwatch'

PhusionPassenger.locate_directories
PhusionPassenger.require_passenger_lib 'admin_tools/instance_registry'
include PhusionPassenger::AdminTools

# Extract a parameter from the Passenger pool status output.
def extract_metric(parameter, output)
  pattern = %r{#{parameter}\s+:\s+(?<result>\d+)}
  match   = output.match(pattern)
  match['result'] if match
end

# Get the Passenger pool status for our active instance,
def get_pool_status(instance)
  request = Net::HTTP::Get.new('/pool.txt')
  # Authenticate the HTTP request to the Passenger API.
  request.basic_auth('ro_admin', instance.read_only_admin_password)
  # Request pool status
  response = instance.http_request('agents.s/core_api', request)
  response.body
end

# Generate the metric to report to CloudWatch.
def build_cloudwatch_metric(metric_name, value, instance_id:, timestamp: Time.now)
  {
    metric_name:        metric_name,
    timestamp:          timestamp,
    value:              value,
    storage_resolution: 1,
    dimensions:         [
      {
        name:   'InstanceId',
        value:  instance_id
      }
    ]
  }
end

instances = InstanceRegistry.new.list
if instances.count > 1
  $stderr.puts 'Multiple Passenger instances... not sure which to use. Exiting.'
  exit(1)
end

# Get pool status from Passenger instance.
instance  = instances.first
output    = get_pool_status(instance)

# Extract key metrics from Passenger output.
timestamp           = Time.now
process_count       = extract_metric('Processes', output).to_i
request_queue_size  = extract_metric('Requests in queue', output).to_i

# Get current instance ID
instance_doc = JSON.parse(Net::HTTP.get(URI('http://169.254.169.254/latest/dynamic/instance-identity/document')))
instance_id = instance_doc['instanceId']
region = instance_doc['region']
ENV['AWS_REGION'] ||= region

# Report metrics to AWS CloudWatch.
cloudwatch = Aws::CloudWatch::Client.new
cloudwatch.put_metric_data(
  namespace:    'Passenger',
  metric_data:  [
    build_cloudwatch_metric('ProcessCount',     process_count,      instance_id:  instance_id,  timestamp: timestamp),
    build_cloudwatch_metric('RequestQueueSize', request_queue_size, instance_id:  instance_id,  timestamp: timestamp)
  ]
)

$stderr.puts "Reported Passenger process count of #{process_count} and request queue size of #{request_queue_size} to CloudWatch."