412cd70d3a
Adds the ability to create alternative backends. Alternative backends enable traffic shaping by sharing a single location but routing to different backends depending on the TrafficShapingPolicy defined by AlternativeBackends. When the list of upstreams and servers are retrieved, we then call mergeAlternativeBackends which iterates through the paths of every ingress and checks if the backend supporting the path is a AlternativeBackend. If so, we then iterate through the map of servers and find the real backend that the AlternativeBackend should fall under. Once found, the AlternativeBackend is embedded in the list of VirtualBackends for the real backend. If no matching real backend for a AlternativeBackend is found, then the AlternativeBackend is deleted as it cannot be backed by any server.
129 lines
3.6 KiB
Lua
129 lines
3.6 KiB
Lua
-- Original Authors: Shiv Nagarajan & Scott Francis
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-- Accessed: March 12, 2018
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-- Inspiration drawn from:
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-- https://github.com/twitter/finagle/blob/1bc837c4feafc0096e43c0e98516a8e1c50c4421
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-- /finagle-core/src/main/scala/com/twitter/finagle/loadbalancer/PeakEwma.scala
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local util = require("util")
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local split = require("util.split")
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local DECAY_TIME = 10 -- this value is in seconds
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local PICK_SET_SIZE = 2
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local balancer_ewma = {}
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local balancer_ewma_last_touched_at = {}
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local _M = { name = "ewma" }
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local function decay_ewma(ewma, last_touched_at, rtt, now)
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local td = now - last_touched_at
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td = (td > 0) and td or 0
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local weight = math.exp(-td/DECAY_TIME)
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ewma = ewma * weight + rtt * (1.0 - weight)
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return ewma
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end
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local function get_or_update_ewma(upstream, rtt, update)
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local ewma = balancer_ewma[upstream] or 0
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local now = ngx.now()
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local last_touched_at = balancer_ewma_last_touched_at[upstream] or 0
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ewma = decay_ewma(ewma, last_touched_at, rtt, now)
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if not update then
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return ewma, nil
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end
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balancer_ewma_last_touched_at[upstream] = now
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balancer_ewma[upstream] = ewma
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return ewma, nil
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end
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local function score(upstream)
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-- Original implementation used names
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-- Endpoints don't have names, so passing in IP:Port as key instead
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local upstream_name = upstream.address .. ":" .. upstream.port
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return get_or_update_ewma(upstream_name, 0, false)
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end
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-- implementation similar to https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
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-- or https://en.wikipedia.org/wiki/Random_permutation
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-- loop from 1 .. k
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-- pick a random value r from the remaining set of unpicked values (i .. n)
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-- swap the value at position i with the value at position r
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local function shuffle_peers(peers, k)
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for i=1, k do
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local rand_index = math.random(i,#peers)
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peers[i], peers[rand_index] = peers[rand_index], peers[i]
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end
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-- peers[1 .. k] will now contain a randomly selected k from #peers
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end
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local function pick_and_score(peers, k)
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shuffle_peers(peers, k)
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local lowest_score_index = 1
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local lowest_score = score(peers[lowest_score_index])
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for i = 2, k do
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local new_score = score(peers[i])
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if new_score < lowest_score then
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lowest_score_index, lowest_score = i, new_score
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end
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end
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return peers[lowest_score_index]
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end
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function _M.balance(self)
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local peers = self.peers
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local endpoint = peers[1]
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if #peers > 1 then
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local k = (#peers < PICK_SET_SIZE) and #peers or PICK_SET_SIZE
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local peer_copy = util.deepcopy(peers)
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endpoint = pick_and_score(peer_copy, k)
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end
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-- TODO(elvinefendi) move this processing to _M.sync
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return endpoint.address .. ":" .. endpoint.port
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end
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function _M.after_balance(_)
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local response_time = tonumber(split.get_first_value(ngx.var.upstream_response_time)) or 0
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local connect_time = tonumber(split.get_first_value(ngx.var.upstream_connect_time)) or 0
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local rtt = connect_time + response_time
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local upstream = split.get_first_value(ngx.var.upstream_addr)
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if util.is_blank(upstream) then
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return
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end
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get_or_update_ewma(upstream, rtt, true)
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end
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function _M.sync(self, backend)
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self.traffic_shaping_policy = backend.trafficShapingPolicy
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self.alternative_backends = backend.alternativeBackends
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local changed = not util.deep_compare(self.peers, backend.endpoints)
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if not changed then
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return
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end
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self.peers = backend.endpoints
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-- TODO: Reset state of EWMA per backend
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balancer_ewma = {}
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balancer_ewma_last_touched_at = {}
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end
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function _M.new(self, backend)
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local o = {
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peers = backend.endpoints,
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}
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setmetatable(o, self)
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self.__index = self
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return o
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end
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return _M
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