add luacheck to lint lua files (kubernetes#2205)

.luacheckrc

@@ -0,0 +1,2 @@
+std = 'ngx_lua'
+globals = {'_'}

.travis.yml

@@ -7,6 +7,11 @@ services:
 
 language: go
 
+addons:
+  apt:
+    packages:
+    - luarocks
+
 notifications:
   email:
     on_failure: always
@@ -32,6 +37,8 @@ jobs:
   include:
   - stage: Static Check
     script:
+    - sudo luarocks install luacheck
+    - make luacheck
     - go get github.com/golang/lint/golint
     - make verify-all
   - stage: Coverage

Makefile

@@ -180,6 +180,10 @@ cover:
 vet:
 	@go vet $(shell go list ${PKG}/... | grep -v vendor)
 
+.PHONY: luacheck
+luacheck:
+	luacheck -q ./rootfs/etc/nginx/lua/
+
 .PHONY: release
 release: all-container all-push
 	echo "done"

rootfs/etc/nginx/lua/balancer.lua

@@ -6,11 +6,11 @@ local lrucache = require("resty.lrucache")
 local resty_lock = require("resty.lock")
 
 -- measured in seconds
--- for an Nginx worker to pick up the new list of upstream peers 
+-- for an Nginx worker to pick up the new list of upstream peers
 -- it will take <the delay until controller POSTed the backend object to the Nginx endpoint> + BACKENDS_SYNC_INTERVAL
 local BACKENDS_SYNC_INTERVAL = 1
 
-ROUND_ROBIN_LOCK_KEY = "round_robin"
+local ROUND_ROBIN_LOCK_KEY = "round_robin"
 
 local round_robin_state = ngx.shared.round_robin_state
 
@@ -37,8 +37,8 @@ local function balance()
 
   -- Round-Robin
   round_robin_lock:lock(backend_name .. ROUND_ROBIN_LOCK_KEY)
-  local index = round_robin_state:get(backend_name)
-  local index, endpoint = next(backend.endpoints, index)
+  local last_index = round_robin_state:get(backend_name)
+  local index, endpoint = next(backend.endpoints, last_index)
   if not index then
     index = 1
     endpoint = backend.endpoints[index]
@@ -96,7 +96,8 @@ function _M.call()
 
   local host, port = balance()
 
-  local ok, err = ngx_balancer.set_current_peer(host, port)
+  local ok
+  ok, err = ngx_balancer.set_current_peer(host, port)
   if ok then
     ngx.log(ngx.INFO, "current peer is set to " .. host .. ":" .. port)
   else