use roundrobin from lua-resty-balancer library and refactor balancer.lua

rootfs/etc/nginx/lua/balancer/resty.lua

@@ -0,0 +1,68 @@
+local resty_roundrobin = require("resty.roundrobin")
+local resty_chash = require("resty.chash")
+local util = require("util")
+
+local _M = {}
+local instances = {}
+
+local function get_resty_balancer_nodes(endpoints)
+  local nodes = {}
+  local weight = 1
+
+  for _, endpoint in pairs(endpoints) do
+    local endpoint_string = endpoint.address .. ":" .. endpoint.port
+    nodes[endpoint_string] = weight
+  end
+
+  return nodes
+end
+
+local function init_resty_balancer(factory, instance, endpoints)
+  local nodes = get_resty_balancer_nodes(endpoints)
+
+  if instance then
+    instance:reinit(nodes)
+  else
+    instance = factory:new(nodes)
+  end
+
+  return instance
+end
+
+function _M.balance(backend)
+  local instance = instances[backend.name]
+  if not instance then
+    return nil
+  end
+
+  local endpoint_string
+  if backend["upstream-hash-by"] then
+    local key = util.lua_ngx_var(backend["upstream-hash-by"])
+    endpoint_string = instance:find(key)
+  else
+    endpoint_string = instance:find()
+  end
+
+  local address, port = util.split_pair(endpoint_string, ":")
+  return { address = address, port = port }
+end
+
+function _M.reinit(backend)
+  local instance = instances[backend.name]
+  local factory = resty_roundrobin
+  if backend["upstream-hash-by"] then
+    factory = resty_chash
+  end
+
+  if instance then
+    local mt = getmetatable(instance)
+    if mt.__index ~= factory then
+      ngx.log(ngx.INFO, "LB algorithm has been changed, resetting the instance")
+      instance = nil
+    end
+  end
+
+  instances[backend.name] = init_resty_balancer(factory, instance, backend.endpoints)
+end
+
+return _M