diff --git a/lib/resty/core.lua b/lib/resty/core.lua
index 0f31e9da9..e52fc5823 100644
--- a/lib/resty/core.lua
+++ b/lib/resty/core.lua
@@ -3,26 +3,26 @@
 local subsystem = ngx.config.subsystem
 
 
+-- regex module should be loaded first to inject ngx.re for other modules
 require "resty.core.regex"
+
 require "resty.core.shdict"
 require "resty.core.time"
 
 
 if subsystem == 'http' then
-    require "resty.core.uri"
-    require "resty.core.hash"
     require "resty.core.base64"
-    require "resty.core.regex"
-    require "resty.core.exit"
-    require "resty.core.var"
     require "resty.core.ctx"
+    require "resty.core.exit"
+    require "resty.core.hash"
     require "resty.core.misc"
+    require "resty.core.ndk"
+    require "resty.core.phase"
     require "resty.core.request"
     require "resty.core.response"
-    require "resty.core.time"
+    require "resty.core.uri"
+    require "resty.core.var"
     require "resty.core.worker"
-    require "resty.core.phase"
-    require "resty.core.ndk"
 end
 
 
diff --git a/lib/resty/core/base64.lua b/lib/resty/core/base64.lua
index 981424cc7..92b4bc5a1 100644
--- a/lib/resty/core/base64.lua
+++ b/lib/resty/core/base64.lua
@@ -1,9 +1,11 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
-local ffi = require 'ffi'
 local base = require "resty.core.base"
+base.allows_subsystem('http')
+
 
+local ffi = require 'ffi'
 local ffi_string = ffi.string
 local C = ffi.C
 local ngx = ngx
diff --git a/lib/resty/core/ctx.lua b/lib/resty/core/ctx.lua
index e348a7eb4..91c4dc9bc 100644
--- a/lib/resty/core/ctx.lua
+++ b/lib/resty/core/ctx.lua
@@ -1,9 +1,12 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
+local base = require "resty.core.base"
+base.allows_subsystem('http')
+
+
 local ffi = require 'ffi'
 local debug = require 'debug'
-local base = require "resty.core.base"
 local misc = require "resty.core.misc"
 
 
diff --git a/lib/resty/core/exit.lua b/lib/resty/core/exit.lua
index 55d7b6a7c..adc405ed6 100644
--- a/lib/resty/core/exit.lua
+++ b/lib/resty/core/exit.lua
@@ -1,12 +1,15 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
+local base = require "resty.core.base"
+base.allows_subsystem('http')
+
+
 local ffi = require 'ffi'
 local ffi_string = ffi.string
 local C = ffi.C
 local ngx = ngx
 local error = error
-local base = require "resty.core.base"
 local get_string_buf = base.get_string_buf
 local get_size_ptr = base.get_size_ptr
 local get_request = base.get_request
diff --git a/lib/resty/core/hash.lua b/lib/resty/core/hash.lua
index de97270c3..69a47ee5c 100644
--- a/lib/resty/core/hash.lua
+++ b/lib/resty/core/hash.lua
@@ -1,6 +1,10 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
+local base = require "resty.core.base"
+base.allows_subsystem('http')
+
+
 local ffi = require 'ffi'
 local ffi_string = ffi.string
 local ffi_new = ffi.new
@@ -9,7 +13,6 @@ local ngx = ngx
 local type = type
 local tostring = tostring
 local error = error
-local base = require "resty.core.base"
 
 
 ffi.cdef[[
diff --git a/lib/resty/core/misc.lua b/lib/resty/core/misc.lua
index cd056dcca..9a093ba25 100644
--- a/lib/resty/core/misc.lua
+++ b/lib/resty/core/misc.lua
@@ -2,9 +2,10 @@
 
 
 local base = require "resty.core.base"
-local ffi = require "ffi"
+base.allows_subsystem('http')
 
 
+local ffi = require "ffi"
 local FFI_NO_REQ_CTX = base.FFI_NO_REQ_CTX
 local FFI_BAD_CONTEXT = base.FFI_BAD_CONTEXT
 local new_tab = base.new_tab
diff --git a/lib/resty/core/phase.lua b/lib/resty/core/phase.lua
index e8fc3bfe8..f16acf9ea 100644
--- a/lib/resty/core/phase.lua
+++ b/lib/resty/core/phase.lua
@@ -1,6 +1,8 @@
-local ffi = require 'ffi'
 local base = require "resty.core.base"
+base.allows_subsystem('http')
+
 
+local ffi = require 'ffi'
 local C = ffi.C
 local FFI_ERROR = base.FFI_ERROR
 local get_request = base.get_request
diff --git a/lib/resty/core/request.lua b/lib/resty/core/request.lua
index 895d1fc4a..60b4ab2ba 100644
--- a/lib/resty/core/request.lua
+++ b/lib/resty/core/request.lua
@@ -1,10 +1,11 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
-local ffi = require 'ffi'
 local base = require "resty.core.base"
+base.allows_subsystem('http')
 
 
+local ffi = require 'ffi'
 local FFI_BAD_CONTEXT = base.FFI_BAD_CONTEXT
 local FFI_DECLINED = base.FFI_DECLINED
 local FFI_OK = base.FFI_OK
diff --git a/lib/resty/core/response.lua b/lib/resty/core/response.lua
index c9610d2c0..7eef43c45 100644
--- a/lib/resty/core/response.lua
+++ b/lib/resty/core/response.lua
@@ -1,10 +1,11 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
-local ffi = require 'ffi'
 local base = require "resty.core.base"
+base.allows_subsystem('http')
 
 
+local ffi = require 'ffi'
 local C = ffi.C
 local ffi_cast = ffi.cast
 local ffi_str = ffi.string
diff --git a/lib/resty/core/uri.lua b/lib/resty/core/uri.lua
index af0e65572..8dd09c170 100644
--- a/lib/resty/core/uri.lua
+++ b/lib/resty/core/uri.lua
@@ -1,13 +1,16 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
+local base = require "resty.core.base"
+base.allows_subsystem('http')
+
+
 local ffi = require 'ffi'
 local ffi_string = ffi.string
 local C = ffi.C
 local ngx = ngx
 local type = type
 local tostring = tostring
-local base = require "resty.core.base"
 local get_string_buf = base.get_string_buf
 
 
diff --git a/lib/resty/core/var.lua b/lib/resty/core/var.lua
index 106c01be8..8d837f03b 100644
--- a/lib/resty/core/var.lua
+++ b/lib/resty/core/var.lua
@@ -1,9 +1,11 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
-local ffi = require 'ffi'
 local base = require "resty.core.base"
+base.allows_subsystem('http')
+
 
+local ffi = require 'ffi'
 local ffi_new = ffi.new
 local ffi_str = ffi.string
 local C = ffi.C
diff --git a/lib/resty/core/worker.lua b/lib/resty/core/worker.lua
index 0da8086cc..4cb87dfc6 100644
--- a/lib/resty/core/worker.lua
+++ b/lib/resty/core/worker.lua
@@ -1,10 +1,11 @@
 -- Copyright (C) Yichun Zhang (agentzh)
 
 
-local ffi = require 'ffi'
 local base = require "resty.core.base"
+base.allows_subsystem('http')
 
 
+local ffi = require 'ffi'
 local C = ffi.C