feature: Round Robin with optional random start (openresty#26)

* Round Robin with optional random start

* make random start a default and only behaviour

Author: ElvinEfendi

README.markdown

@@ -98,6 +98,7 @@ Synopsis
 
             local rr_up = package.loaded.my_rr_up
 
+            -- Note that Round Robin picks the first server randomly
             local server = rr_up:find()
 
             assert(b.set_current_peer(server))

lib/resty/roundrobin.lua

@@ -3,6 +3,7 @@ local pairs = pairs
 local next = next
 local tonumber = tonumber
 local setmetatable = setmetatable
+local math_random = math.random
 
 
 local _M = {}
@@ -46,18 +47,35 @@ local function get_gcd(nodes)
     return only_key, gcd, max_weight
 end
 
+local function get_random_node_id(nodes)
+    local count = 0
+    for _, _ in pairs(nodes) do
+        count = count + 1
+    end
+
+    local id = nil
+    local random_index = math_random(count)
+
+    for _ = 1, random_index do
+        id = next(nodes, id)
+    end
+
+    return id
+end
+
 
 function _M.new(_, nodes)
     local newnodes = copy(nodes)
     local only_key, gcd, max_weight = get_gcd(newnodes)
+    local last_id = get_random_node_id(nodes)
 
     local self = {
         nodes = newnodes,  -- it's safer to copy one
         only_key = only_key,
         max_weight = max_weight,
         gcd = gcd,
         cw = max_weight,
-        last_id = nil,
+        last_id = last_id,
     }
     return setmetatable(self, mt)
 end
@@ -68,7 +86,7 @@ function _M.reinit(self, nodes)
     self.only_key, self.gcd, self.max_weight = get_gcd(newnodes)
 
     self.nodes = newnodes
-    self.last_id = nil
+    self.last_id = get_random_node_id(nodes)
     self.cw = self.max_weight
 end
 

t/roundrobin.t

@@ -28,6 +28,8 @@ __DATA__
 --- config
     location /t {
         content_by_lua_block {
+            math.randomseed(75098)
+
             local roundrobin = require "resty.roundrobin"
 
             local servers = {
@@ -53,7 +55,6 @@ GET /t
 gcd: 2
 id: server1
 id: server1
-id: server1
 id: server2
 id: server1
 id: server2
@@ -65,6 +66,7 @@ id: server2
 id: server1
 id: server2
 id: server3
+id: server1
 --- no_error_log
 [error]
 
@@ -75,6 +77,8 @@ id: server3
 --- config
     location /t {
         content_by_lua_block {
+            math.randomseed(75098)
+
             local roundrobin = require "resty.roundrobin"
 
             local servers = {
@@ -104,8 +108,54 @@ id: server3
 --- request
 GET /t
 --- response_body
-server1: 50001
+server1: 50000
 server3: 16666
-server2: 33333
+server2: 33334
+--- no_error_log
+[error]
+
+
+
+=== TEST 3: random start
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            math.randomseed(9975098)
+
+            local roundrobin = require "resty.roundrobin"
+
+            local servers = {
+                ["server1"] = 1,
+                ["server2"] = 1,
+                ["server3"] = 1,
+                ["server4"] = 1,
+            }
+
+            local rr = roundrobin:new(servers, true)
+            local id = rr:find()
+            ngx.say(id)
+
+            math.randomseed(11175098)
+
+            local new_servers = {
+                ["server1"] = 1,
+                ["server2"] = 1,
+                ["server3"] = 1,
+                ["server4"] = 1,
+                ["server5"] = 1,
+                ["server6"] = 1,
+            }
+
+            rr:reinit(new_servers)
+            id = rr:find()
+            ngx.say(id)
+        }
+    }
+--- request
+GET /t
+--- response_body
+server2
+server5
 --- no_error_log
 [error]