Server balancing by file ID

server_balancing.rb

require 'digest/sha1'
#
# servers -> [3, 5, 8]
# история количеств серверов
#
def fetch_server_no(acc, servers)
  while server = servers.pop do
    last = servers.last.to_i
    # Для более равномерного размазывания по серверам
    rest = Digest::SHA1.hexdigest("#{acc}_#{server}").to_i(16) % server
    rest = server if rest == 0
    if last == 0 || rest > last
      current = server - last
      no = acc % current
      no = current if no == 0
      no += last
      return no
    end
  end
end

servers = {}
(1..100000).each do |file|
  no = fetch_server_no(file, [3,5,8,12,15,20])
  servers[no] ||= 0
  servers[no] += 1
end
servers.sort

# =>
# [[1, 4921],
#  [2, 5008],
#  [3, 4925],
#  [4, 5130],
#  [5, 4908],
#  [6, 5124],
#  [7, 4936],
#  [8, 4962],
#  [9, 5023],
#  [10, 5081],
#  [11, 5029],
#  [12, 4840],
#  [13, 5003],
#  [14, 4967],
#  [15, 4966],
#  [16, 5006],
#  [17, 5072],
#  [18, 5013],
#  [19, 5033],
#  [20, 5053]]