with-magellan

#!/usr/bin/env ruby

# Usage:
# bin/with-magellan bundle exec unicorn
# The binary will execute `bundle exec unicorn` and watch for endpoint status changes in Magellan

require 'net/http'
require 'json'
require "English"

parent = $PID
hostname = "demo"
borg_service = "development_kirs_sb"

def get_magellan_service(service_name)
  request = Net::HTTP::Get.new("/services/#{service_name}")
  url = URI.parse("http://192.168.64.103:8438")
  Net::HTTP.start(url.host, url.port) do |http|
    response = http.request(request)
    return unless response.code == "200"
    JSON.parse(response.body)
  end
end

def get_magellan_status(service_name, hostname)
  service = get_magellan_service(service_name)
  return unless service
  instance = service.fetch("instances").find { |i| i.fetch("endpoint") == hostname }
  unless instance
    raise "Could not find an instance for #{hostname}"
  end
  status = instance.fetch("body").fetch("status")
  puts "<<< watching magellan status: #{status}"
  status
end

def subscribe_to_magellan_status
  loop do
    sleep 5
    status = get_magellan_status(borg_service, hostname)
    yield(status)
  end
end

# Before running the actual process, check if it's supposed to be active
# If it's not active, sleep and check it again
# Eventually it will be marked as active, we will exit from the script and runit
# will start the service again
status = get_magellan_status(borg_service, hostname)
if status != "active"
  puts "The process should not be up..."

  subscribe_to_magellan_status do |status|
    if status == "active"
      puts "The process became active. Restarting..."
      exit
    end
  end
end

# Watch status updates in the work while running the process
# If we OOR the process, kill the parent
# On the next run, runit won't start it and will wait until the process becomes active
fork do
  subscribe_to_magellan_status do |status|
    if status != "active"
      puts "The process is not supposed to be running anymore. Killing it..."
      Process.kill("SIGTERM", parent)
      exit
    end
  end
end

exec(*ARGV)