How to chnage the timezone of ruby Time object

change_tz.rb

require 'tzinfo'
require 'date'

TIMEZONES = {
  'us-east-1' => 'US/Eastern',
  'us-west-1' => 'US/Pacific',
  'us-west-2' => 'US/Pacific',
  'eu-west-1' => 'GB',
  'ap-southeast-1' => 'Singapore',
  'ap-northeast-1' => 'Japan',
  'sa-east-1' => 'Sao_Paulo',
  }

def time_at_tz(time, tz_or_region)
  timezone = if TIMEZONES[tz_or_region]
               TIMEZONES[tz_or_region]
             else
               tz_or_region
             end
  tz = TZInfo::Timezone.get(timezone)
  value = case time
          when Integer
            Time.at(time).utc
          when Time
            time.utc
          else
            raise ArgumentError.new("Invalid time. #{time}")
          end
  local_time = tz.utc_to_local value
end

# test
value = 1429066136
puts Time.at value
puts (Time.at value).utc
puts time_at_tz(value, 'US/Eastern')
puts time_at_tz(value, 'ap-northeast-1')

result.txt

2015-04-14 19:48:56 -0700
2015-04-15 02:48:56 UTC
2015-04-14 22:48:56 UTC
2015-04-15 11:48:56 UTC

Since the Ruby Time class supports two timezones(utc and local), timezone of returned time object has always UTC timezone.
https://github.com/tzinfo/tzinfo