feature: implement ewma balancer for upstream node (#2001)

ewma is a different balancing implementation that will generate a weight for every backend IP based on the last server response time, basically it tries to dispatch more requests to the backends that reply faster, supposing that they are less loaded.

fix #1996

LICENSE

@@ -199,3 +199,14 @@
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
+
+=======================================================================
+Apache ApiSix Subcomponents:
+
+The Apache ApiSix project contains subcomponents with separate copyright
+notices and license terms. Your use of the source code for the these
+subcomponents is subject to the terms and conditions of the following
+licenses.
+
+   ewma.lua file from kubernetes/ingress-nginx: https://github.com/kubernetes/ingress-nginx Apache 2.0
+

apisix/balancer.lua

@@ -30,9 +30,9 @@ local module_name = "balancer"
 local pickers = {
     roundrobin = require("apisix.balancer.roundrobin"),
     chash = require("apisix.balancer.chash"),
+    ewma = require("apisix.balancer.ewma")
 }
 
-
 local lrucache_server_picker = core.lrucache.new({
     ttl = 300, count = 256
 })
@@ -245,7 +245,7 @@ local function pick_server(route, ctx)
         core.log.error("failed to parse server addr: ", server, " err: ", err)
         return core.response.exit(502)
     end
-
+    ctx.server_picker = server_picker
     return res
 end
 

apisix/balancer/ewma.lua

@@ -0,0 +1,191 @@
+--
+-- Licensed to the Apache Software Foundation (ASF) under one or more
+-- contributor license agreements.  See the NOTICE file distributed with
+-- this work for additional information regarding copyright ownership.
+-- The ASF licenses this file to You under the Apache License, Version 2.0
+-- (the "License"); you may not use this file except in compliance with
+-- the License.  You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+--
+
+
+local core = require("apisix.core")
+local ngx = ngx
+local ngx_shared = ngx.shared
+local ngx_now = ngx.now
+local math = math
+local pairs = pairs
+local next = next
+local tonumber = tonumber
+
+local _M = {}
+local DECAY_TIME = 10 -- this value is in seconds
+
+local shm_ewma = ngx_shared.balancer_ewma
+local shm_last_touched_at= ngx_shared.balancer_ewma_last_touched_at
+
+local lrucache_addr = core.lrucache.new({
+    ttl = 300, count = 1024
+})
+local lrucache_trans_format = core.lrucache.new({
+    ttl = 300, count = 256
+})
+
+
+local function decay_ewma(ewma, last_touched_at, rtt, now)
+    local td = now - last_touched_at
+    td = math.max(td, 0)
+    local weight = math.exp(-td / DECAY_TIME)
+
+    ewma = ewma * weight + rtt * (1.0 - weight)
+    return ewma
+end
+
+
+local function store_stats(upstream, ewma, now)
+    local success, err, forcible = shm_last_touched_at:set(upstream, now)
+    if not success then
+        core.log.error("balancer_ewma_last_touched_at:set failed ", err)
+    end
+    if forcible then
+        core.log.warn("balancer_ewma_last_touched_at:set valid items forcibly overwritten")
+    end
+
+    success, err, forcible = shm_ewma:set(upstream, ewma)
+    if not success then
+        core.log.error("balancer_ewma:set failed ", err)
+    end
+    if forcible then
+        core.log.warn("balancer_ewma:set valid items forcibly overwritten")
+    end
+end
+
+
+local function get_or_update_ewma(upstream, rtt, update)
+    local ewma = shm_ewma:get(upstream) or 0
+    local now = ngx_now()
+    local last_touched_at = shm_last_touched_at:get(upstream) or 0
+    ewma = decay_ewma(ewma, last_touched_at, rtt, now)
+
+    if not update then
+        return ewma
+    end
+
+    store_stats(upstream, ewma, now)
+
+    return ewma
+end
+
+
+local function score(upstream)
+    -- Original implementation used names
+    -- Endpoints don't have names, so passing in host:Port as key instead
+    local upstream_name = upstream.host .. ":" .. upstream.port
+    return get_or_update_ewma(upstream_name, 0, false)
+end
+
+
+local function pick_and_score(peers)
+    local lowest_score_index = 1
+    local lowest_score = score(peers[lowest_score_index])
+    for i = 2, #peers do
+        local new_score = score(peers[i])
+        if new_score < lowest_score then
+            lowest_score_index, lowest_score = i, new_score
+        end
+    end
+
+    return peers[lowest_score_index], lowest_score
+end
+
+
+local function parse_addr(addr)
+    local host, port, err = core.utils.parse_addr(addr)
+    return {host = host, port = port}, err
+end
+
+
+local function _trans_format(up_nodes)
+    -- trans
+    --{"1.2.3.4:80":100,"5.6.7.8:8080":100}
+    -- into
+    -- [{"host":"1.2.3.4","port":"80"},{"host":"5.6.7.8","port":"8080"}]
+    local peers = {}
+    local res, err
+
+    for addr, _ in pairs(up_nodes) do
+        res, err = lrucache_addr(addr, nil, parse_addr, addr)
+        if not err then
+            core.table.insert(peers, res)
+        else
+            core.log.error('parse_addr error: ', addr, err)
+        end
+    end
+
+    return next(peers) and peers or nil
+end
+
+
+local function _ewma_find(ctx, up_nodes)
+    local peers
+    local endpoint
+
+    if not up_nodes
+       or core.table.nkeys(up_nodes) == 0 then
+        return nil, 'up_nodes empty'
+    end
+
+    peers = lrucache_trans_format(ctx.upstream_key, ctx.upstream_version,
+                                  _trans_format, up_nodes)
+    if not peers then
+        return nil, 'up_nodes trans error'
+    end
+
+    if #peers > 1 then
+        endpoint = pick_and_score(peers)
+    else
+        endpoint = peers[1]
+    end
+
+    return endpoint.host .. ":" .. endpoint.port
+end
+
+
+local function _ewma_after_balance(ctx)
+    local response_time = tonumber(ctx.var.upstream_response_time) or 0
+    local connect_time = tonumber(ctx.var.upstream_connect_time) or 0
+    local rtt = connect_time + response_time
+    local upstream = ctx.var.upstream_addr
+
+    if not upstream then
+        return nil, "no upstream addr found"
+    end
+
+    return get_or_update_ewma(upstream, rtt, true)
+end
+
+
+function _M.new(up_nodes, upstream)
+    if not shm_ewma
+       or not shm_last_touched_at then
+        return nil, "dictionary not find"
+    end
+
+    return {
+        upstream = upstream,
+        get = function (ctx)
+            return _ewma_find(ctx, up_nodes)
+        end,
+        after_balance = _ewma_after_balance
+    }
+end
+
+
+return _M

apisix/init.lua

@@ -651,6 +651,10 @@ function _M.http_log_phase()
     local api_ctx = common_phase("log")
     healcheck_passive(api_ctx)
 
+    if api_ctx.server_picker and api_ctx.server_picker.after_balance then
+        api_ctx.server_picker.after_balance(api_ctx)
+    end
+
     if api_ctx.uri_parse_param then
         core.tablepool.release("uri_parse_param", api_ctx.uri_parse_param)
     end

apisix/schema_def.lua

@@ -311,7 +311,7 @@ local upstream_schema = {
         type = {
             description = "algorithms of load balancing",
             type = "string",
-            enum = {"chash", "roundrobin"}
+            enum = {"chash", "roundrobin", "ewma"}
         },
         checks = health_checker,
         hash_on = {

bin/apisix

@@ -181,6 +181,9 @@ http {
     lua_shared_dict worker-events        10m;
     lua_shared_dict lrucache-lock        10m;
     lua_shared_dict skywalking-tracing-buffer    100m;
+    lua_shared_dict balancer_ewma        10m;
+    lua_shared_dict balancer_ewma_locks  10m;
+    lua_shared_dict balancer_ewma_last_touched_at 10m;
 
     # for openid-connect plugin
     lua_shared_dict discovery             1m; # cache for discovery metadata documents

doc/admin-api.md

@@ -493,7 +493,7 @@ In addition to the basic complex equalization algorithm selection, APISIX's Upst
 
 |Name    |Optional|Description|
 |-------         |-----|------|
-|type            |required|`roundrobin` supports the weight of the load, `chash` consistency hash, pick one of them.|
+|type            |required|`roundrobin` supports the weight of the load, `chash` consistency hash,`ewma` minimum latency ,pick one of them.see https://en.wikipedia.org/wiki/EWMA_chart for details|
 |nodes           |required if `k8s_deployment_info` not configured|Hash table, the key of the internal element is the upstream machine address list, the format is `Address + Port`, where the address part can be IP or domain name, such as `192.168.1.100:80`, `foo.com:80`, etc. Value is the weight of the node. In particular, when the weight value is `0`, it has a special meaning, which usually means that the upstream node is invalid and never wants to be selected.|
 |k8s_deployment_info|required if `nodes` not configured|fields: `namespace`、`deploy_name`、`service_name`、`port`、`backend_type`, `port` is number, `backend_type` is `pod` or `service`, others is string. |
 |hash_on         |optional|This option is only valid if the `type` is `chash`. Supported types `vars`(Nginx variables), `header`(custom header), `cookie`, `consumer`, the default value is `vars`.|

t/APISIX.pm

@@ -220,6 +220,9 @@ _EOC_
     lua_shared_dict worker-events        10m;
     lua_shared_dict lrucache-lock        10m;
     lua_shared_dict skywalking-tracing-buffer    100m;
+    lua_shared_dict balancer_ewma         1m;
+    lua_shared_dict balancer_ewma_locks   1m;
+    lua_shared_dict balancer_ewma_last_touched_at  1m;
 
     resolver $dns_addrs_str;
     resolver_timeout 5;

t/lib/server.lua

@@ -68,6 +68,16 @@ function _M.sleep1()
     ngx.say("ok")
 end
 
+function _M.ewma()
+    if ngx.var.server_port == "1981"
+       or ngx.var.server_port == "1982" then
+        ngx.sleep(0.2)
+    else
+        ngx.sleep(0.1)
+    end
+    ngx.print(ngx.var.server_port)
+end
+
 function _M.uri()
     -- ngx.sleep(1)
     ngx.say("uri: ", ngx.var.uri)