ewma improvements
This commit is contained in:
Elvin Efendi
parent
0b375989f3
commit
30b64df10a
6 changed files with 354 additions and 98 deletions
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@ -1,91 +1,151 @@
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local util = require("util")
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local original_ngx = ngx
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local function reset_ngx()
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_G.ngx = original_ngx
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end
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local function mock_ngx(mock)
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local _ngx = mock
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setmetatable(_ngx, { __index = ngx })
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_G.ngx = _ngx
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end
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local function flush_all_ewma_stats()
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ngx.shared.balancer_ewma:flush_all()
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ngx.shared.balancer_ewma_last_touched_at:flush_all()
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end
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local function store_ewma_stats(endpoint_string, ewma, touched_at)
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ngx.shared.balancer_ewma:set(endpoint_string, ewma)
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ngx.shared.balancer_ewma_last_touched_at:set(endpoint_string, touched_at)
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end
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local function assert_ewma_stats(endpoint_string, ewma, touched_at)
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assert.are.equals(ewma, ngx.shared.balancer_ewma:get(endpoint_string))
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assert.are.equals(touched_at, ngx.shared.balancer_ewma_last_touched_at:get(endpoint_string))
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end
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describe("Balancer ewma", function()
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local balancer_ewma = require("balancer.ewma")
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local ngx_now = 1543238266
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local backend, instance
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before_each(function()
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mock_ngx({ now = function() return ngx_now end, var = { balancer_ewma_score = -1 } })
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backend = {
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name = "namespace-service-port", ["load-balance"] = "ewma",
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endpoints = {
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{ address = "10.10.10.1", port = "8080", maxFails = 0, failTimeout = 0 },
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{ address = "10.10.10.2", port = "8080", maxFails = 0, failTimeout = 0 },
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{ address = "10.10.10.3", port = "8080", maxFails = 0, failTimeout = 0 },
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}
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}
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store_ewma_stats("10.10.10.1:8080", 0.2, ngx_now - 1)
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store_ewma_stats("10.10.10.2:8080", 0.3, ngx_now - 5)
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store_ewma_stats("10.10.10.3:8080", 1.2, ngx_now - 20)
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instance = balancer_ewma:new(backend)
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end)
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after_each(function()
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reset_ngx()
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flush_all_ewma_stats()
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end)
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describe("after_balance()", function()
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local ngx_now = 1543238266
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_G.ngx.now = function() return ngx_now end
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_G.ngx.var = { upstream_response_time = "0.25", upstream_connect_time = "0.02", upstream_addr = "10.184.7.40:8080" }
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it("updates EWMA stats", function()
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local backend = {
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name = "my-dummy-backend", ["load-balance"] = "ewma",
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endpoints = { { address = "10.184.7.40", port = "8080", maxFails = 0, failTimeout = 0 } }
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}
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local instance = balancer_ewma:new(backend)
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ngx.var = { upstream_addr = "10.10.10.2:8080", upstream_connect_time = "0.02", upstream_response_time = "0.1" }
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instance:after_balance()
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assert.equal(0.27, instance.ewma[ngx.var.upstream_addr])
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assert.equal(ngx_now, instance.ewma_last_touched_at[ngx.var.upstream_addr])
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local weight = math.exp(-5 / 10)
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local expected_ewma = 0.3 * weight + 0.12 * (1.0 - weight)
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assert.are.equals(expected_ewma, ngx.shared.balancer_ewma:get(ngx.var.upstream_addr))
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assert.are.equals(ngx_now, ngx.shared.balancer_ewma_last_touched_at:get(ngx.var.upstream_addr))
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end)
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end)
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describe("balance()", function()
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it("returns single endpoint when the given backend has only one endpoint", function()
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local backend = {
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name = "my-dummy-backend", ["load-balance"] = "ewma",
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endpoints = { { address = "10.184.7.40", port = "8080", maxFails = 0, failTimeout = 0 } }
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}
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local instance = balancer_ewma:new(backend)
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local single_endpoint_backend = util.deepcopy(backend)
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table.remove(single_endpoint_backend.endpoints, 3)
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table.remove(single_endpoint_backend.endpoints, 2)
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local single_endpoint_instance = balancer_ewma:new(single_endpoint_backend)
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local peer = instance:balance()
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assert.equal("10.184.7.40:8080", peer)
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local peer = single_endpoint_instance:balance()
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assert.are.equals("10.10.10.1:8080", peer)
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assert.are.equals(-1, ngx.var.balancer_ewma_score)
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end)
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it("picks the endpoint with lowest score when there two of them", function()
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local backend = {
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name = "my-dummy-backend", ["load-balance"] = "ewma",
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endpoints = {
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{ address = "10.184.7.40", port = "8080", maxFails = 0, failTimeout = 0 },
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{ address = "10.184.97.100", port = "8080", maxFails = 0, failTimeout = 0 },
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}
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}
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local instance = balancer_ewma:new(backend)
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instance.ewma = { ["10.184.7.40:8080"] = 0.5, ["10.184.97.100:8080"] = 0.3 }
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instance.ewma_last_touched_at = { ["10.184.7.40:8080"] = ngx.now(), ["10.184.97.100:8080"] = ngx.now() }
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it("picks the endpoint with lowest decayed score", function()
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local two_endpoints_backend = util.deepcopy(backend)
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table.remove(two_endpoints_backend.endpoints, 2)
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local two_endpoints_instance = balancer_ewma:new(two_endpoints_backend)
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local peer = instance:balance()
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assert.equal("10.184.97.100:8080", peer)
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local peer = two_endpoints_instance:balance()
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-- even though 10.10.10.1:8080 has a lower ewma score
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-- algorithm picks 10.10.10.3:8080 because its decayed score is even lower
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assert.equal("10.10.10.3:8080", peer)
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assert.are.equals(0.16240233988393523723, ngx.var.balancer_ewma_score)
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end)
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end)
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describe("sync()", function()
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local backend, instance
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before_each(function()
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backend = {
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name = "my-dummy-backend", ["load-balance"] = "ewma",
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endpoints = { { address = "10.184.7.40", port = "8080", maxFails = 0, failTimeout = 0 } }
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}
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instance = balancer_ewma:new(backend)
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end)
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it("does nothing when endpoints do not change", function()
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local new_backend = {
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endpoints = { { address = "10.184.7.40", port = "8080", maxFails = 0, failTimeout = 0 } }
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}
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instance:sync(new_backend)
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end)
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it("updates endpoints", function()
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local new_backend = {
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endpoints = {
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{ address = "10.184.7.40", port = "8080", maxFails = 0, failTimeout = 0 },
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{ address = "10.184.97.100", port = "8080", maxFails = 0, failTimeout = 0 },
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}
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}
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instance:sync(new_backend)
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assert.are.same(new_backend.endpoints, instance.peers)
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end)
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it("resets stats", function()
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it("does not reset stats when endpoints do not change", function()
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local new_backend = util.deepcopy(backend)
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new_backend.endpoints[1].maxFails = 3
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instance:sync(new_backend)
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assert.are.same(new_backend.endpoints, instance.peers)
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assert_ewma_stats("10.10.10.1:8080", 0.2, ngx_now - 1)
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assert_ewma_stats("10.10.10.2:8080", 0.3, ngx_now - 5)
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assert_ewma_stats("10.10.10.3:8080", 1.2, ngx_now - 20)
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end)
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it("updates peers, deletes stats for old endpoints and sets average ewma score to new ones", function()
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local new_backend = util.deepcopy(backend)
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-- existing endpoint 10.10.10.2 got deleted
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-- and replaced with 10.10.10.4
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new_backend.endpoints[2].address = "10.10.10.4"
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-- and there's one new extra endpoint
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table.insert(new_backend.endpoints, { address = "10.10.10.5", port = "8080", maxFails = 0, failTimeout = 0 })
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instance:sync(new_backend)
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assert.are.same(new_backend.endpoints, instance.peers)
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assert_ewma_stats("10.10.10.1:8080", 0.2, ngx_now - 1)
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assert_ewma_stats("10.10.10.2:8080", nil, nil)
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assert_ewma_stats("10.10.10.3:8080", 1.2, ngx_now - 20)
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local slow_start_ewma = (0.2 + 1.2) / 2
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assert_ewma_stats("10.10.10.4:8080", slow_start_ewma, ngx_now)
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assert_ewma_stats("10.10.10.5:8080", slow_start_ewma, ngx_now)
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end)
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it("does not set slow_start_ewma when there is no existing ewma", function()
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local new_backend = util.deepcopy(backend)
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table.insert(new_backend.endpoints, { address = "10.10.10.4", port = "8080", maxFails = 0, failTimeout = 0 })
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-- when the LB algorithm instance is just instantiated it won't have any
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-- ewma value set for the initial endpoints (because it has not processed any request yet),
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-- this test is trying to simulate that by flushing existing ewma values
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flush_all_ewma_stats()
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instance:sync(new_backend)
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assert_ewma_stats("10.10.10.1:8080", nil, nil)
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assert_ewma_stats("10.10.10.2:8080", nil, nil)
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assert_ewma_stats("10.10.10.3:8080", nil, nil)
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assert_ewma_stats("10.10.10.4:8080", nil, nil)
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end)
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end)
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end)
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