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<title>Creating hooks and scripts with mod_lua - Apache HTTP Server Version 2.5</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.5</a> &gt; <a href="./">Developer</a></div><div id="page-content"><div id="preamble"><h1>Creating hooks and scripts with mod_lua</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/developer/lua.html" title="English">&nbsp;en&nbsp;</a></p>
</div>
<p>This document expands on the <code class="module"><a href="../mod/mod_lua.html">mod_lua</a></code> documentation and explores
additional ways of using mod_lua for writing hooks and scripts.</p>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#enabling">Optimizing mod_lua for production servers</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#basic_remap">Example 1: A basic remapping module</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#mass_vhost">Example 2: Mass virtual hosting</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#basic_auth">Example 3: A basic authorization hook</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#authz">Example 4: Authorization using LuaAuthzProvider</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#loadbalancing">Example 5: A rudimentary load balancer</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#map_handler">Example 6: Overlays using LuaMapHandler</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#mod_status_lua">Example 6: Basic Lua scripts</a></li>
</ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_lua.html">mod_lua</a></li><li><a href="modguide.html">Developing modules for Apache 2.4</a></li><li><a href="request.html">Request Processing in Apache 2.4</a></li><li><a href="hooks.html">Apache 2.x Hook Functions</a></li><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="introduction" id="introduction">Introduction</a></h2>
<h3><a name="what" id="what">What is mod_lua</a></h3>
<p>
Stuff about what <code class="module"><a href="../mod/mod_lua.html">mod_lua</a></code> is goes here.
</p>
<h3><a name="contents" id="contents">What we will be discussing in this document</a></h3>
<p>
This document will discuss several cases where <code class="module"><a href="../mod/mod_lua.html">mod_lua</a></code> can be used
to either ease up a phase of the request processing or create more transparency in
the logic behind a decision made in a phase.
</p>
<h3><a name="prerequisites" id="prerequisites">Prerequisites</a></h3>
<p>
First and foremost, you are expected to have a basic knowledge of how the Lua
programming language works. In most cases, we will try to be as pedagogical
as possible and link to documents describing the functions used in the
examples, but there are also many cases where it is necessary to either
just assume that "it works" or do some digging yourself into what the hows
and whys of various function calls.
</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="enabling" id="enabling">Optimizing mod_lua for production servers</a></h2>
<h3>Setting a scope for Lua states</h3>
<p>
Setting the right <code class="directive"><a href="../mod/mod_lua.html#luascope">LuaScope</a></code> setting
for your Lua scripts can be essential to your server's
performance. By default, the scope is set to <code>once</code>, which means
that every call to a Lua script will spawn a new Lua state that handles that
script and is destroyed immediately after. This option keeps the memory
footprint of mod_lua low, but also affects the processing speed of a request.
If you have the memory to spare, you can set the scope to <code>thread</code>,
which will make mod_lua spawn a Lua state that lasts the entirety of a thread's
lifetime, speeding up request processing by 2-3 times. Since mod_lua will create
a state for each script, this may be an expensive move, memory-wise, so to
compromise between speed and memory usage, you can choose the <code>server</code>
option to create a pool of Lua states to be used. Each request for a Lua script or
a hook function will then acquire a state from the pool and release it back when it's
done using it, allowing you to still gain a significant performance increase, while
keeping your memory footprint low. Some examples of possible settings are:
</p>
<pre class="prettyprint lang-config">LuaScope once
LuaScope thread
LuaScope server 5 40</pre>
<p>
As a general rule of thumb: If your server has none to low usage, use <code>once</code>
or <code>request</code>, if your server has low to medium usage, use the <code>server</code>
pool, and if it has high usage, use the <code>thread</code> setting. As your server's
load increases, so will the number of states being actively used, and having your scope
set to <code>once/request/conn</code> will stop being beneficial to your memory footprint.
</p>
<p>
<strong>Note:</strong> The <code>min</code> and <code>max</code> settings for the
<code>server</code> scope denotes the minimum and maximum states to keep in a pool per
server <em>process</em>, so keep this below your <code>ThreadsPerChild</code> limit.
</p>
<h3>Using code caching</h3>
<p>
By default, <code class="module"><a href="../mod/mod_lua.html">mod_lua</a></code> stats each Lua script to determine whether a reload
(and thus, a re-interpretation and re-compilation) of a script is required. This is managed
through the <code class="directive"><a href="../mod/mod_lua.html#luacodecache">LuaCodeCache</a></code> directive. If you are running
your scripts on a production server, and you do not need to update them regularly, it may be
advantageous to set this directive to the <code>forever</code> value, which will cause mod_lua
to skip the stat process and always reuse the compiled byte-code from the first access to the
script, thus speeding up the processing. For Lua hooks, this can prove to increase peformance,
while for scripts handled by the <code>lua-script</code> handler, the increase in performance
may be negligible, as files httpd will stat the files regardless.
</p>
<h3>Keeping the scope clean</h3>
<p>
For maximum performance, it is generally recommended that any initialization of libraries,
constants and master tables be kept outside the handle's scope:
</p>
<pre class="prettyprint lang-lua">--[[ This is good practice ]]--
require "string"
require "someLibrary"
local masterTable = {}
local constant = "Foo bar baz"
function handle(r)
do_stuff()
end</pre>
<pre class="prettyprint lang-lua">--[[ This is bad practice ]]--
require "string"
function handle(r)
require "someLibrary"
local masterTable = {}
local constant = "Foo bar baz"
do_stuff()
end</pre>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="basic_remap" id="basic_remap">Example 1: A basic remapping module</a></h2>
<p>
These first examples show how mod_lua can be used to rewrite URIs in the same
way that one could do using <code class="directive"><a href="../mod/mod_alias.html#alias">Alias</a></code> or
<code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code>, but with more clarity
on how the decision-making takes place, as well as allowing for more complex
decisions than would otherwise be allowed with said directives.
</p>
<pre class="prettyprint lang-config">LuaHookTranslateName /path/too/foo.lua remap</pre>
<pre class="prettyprint lang-lua">--[[
Simple remap example.
This example will rewrite /foo/test.bar to the physical file
/internal/test, somewhat like how mod_alias works.
]]--
function remap(r)
-- Test if the URI matches our criteria
local barFile = r.uri:match("/foo/([a-zA-Z0-9]+)%.bar")
if barFile then
r.filename = "/internal/" .. barFile
end
return apache2.OK
end</pre>
<pre class="prettyprint lang-lua">--[[
Advanced remap example.
This example will evaluate some conditions, and based on that,
remap a file to one of two destinations, using a rewrite map.
This is similar to mixing AliasMatch and ProxyPass, but
without them clashing in any way. Assuming we are on example.com, then:
http://example.com/photos/test.png will be rewritten as /uploads/www/test.png
http://example.com/ext/foo.html will be proxied to http://www.external.com/foo.html
URIs that do not match, will be served by their respective default handlers
]]--
local map = {
photos = {
source = [[^/photos/(.+)\.png$]],
destination = [[/uploads/www/$1.png]],
proxy = false
},
externals = {
source = [[^/ext/(.*)$]],
destination = [[http://www.external.com/$1]],
proxy = true
}
}
function interpolateString(s,v)
return s:gsub("%$(%d+)", function(a) return v[tonumber(a)] end)
end
function remap(r)
-- browse through the rewrite map
for key, entry in pairs(map) do
-- Match source regex against URI
local match = r:regex(entry.source, r.uri) then
if match and match[0] then
r.filename = interpolateString(entry.destination, match)
-- Is this a proxied remap?
if entry.proxy then
r.handler = "proxy-server" -- tell mod_proxy to handle this
r.proxyreq = apache2.PROXYREQ_REVERSE -- We'll want to do a reverse proxy
r.filename = "proxy:" .. r.filename -- Add the proxy scheme to the destination
end
return apache2.OK
end
end
return apache2.DECLINED
end</pre>
<p>
bla bla
</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="mass_vhost" id="mass_vhost">Example 2: Mass virtual hosting</a></h2>
<p>
As with simple and advanced rewriting, you can use mod_lua for dynamically
assigning a hostname to a specific document root, much like
<code class="module"><a href="../mod/mod_vhost_alias.html">mod_vhost_alias</a></code> does, but with more control over what goes
where. This could be as simple as a table holding the information about which
host goes into which folder, or more advanced, using a database holding the
document roots of each hostname.
</p>
<pre class="prettyprint lang-config">LuaHookTranslateName /path/too/foo.lua mass_vhost</pre>
<pre class="prettyprint lang-lua">--[[
Simple mass vhost script
This example will check a map for a virtual host and rewrite filename and
document root accordingly.
]]--
local vhosts = {
{ domain = "example.com", home = "/www/example.com" },
{ domain = "example.org", home = "/nfs/ext1/example.org" }
}
function mass_vhost(r)
-- Match against our hostname
for key, entry in pairs(vhosts) do
-- match against either host or *.host:
if apache2.strcmp_match(r.hostname, entry.domain) or
apache2.strcmp_match(r.hostname, "*." .. entry.domain) then
-- If it matches, rewrite filename and set document root
local filename = r.filename:sub(r.document_root:len()+1)
r.filename = entry.home .. filename
apahce2.set_document_root(entry.home)
return apache2.OK
end
end
return apache2.DECLINED
end</pre>
<pre class="prettyprint lang-lua">--[[
Advanced mass virtual hosting
This example will query a database for vhost entries and save them for
60 seconds before checking for updates. For best performance, such scripts
should generally be run with LuaScope set to 'thread' or 'server'
]]--
local cached_vhosts = {}
local timeout = 60
-- Function for querying the database for saved vhost entries
function query_vhosts(r)
local host = r.hostname
if not cached_vhosts[host] or (cached_vhosts[host] and cached_vhosts[host].updated &lt; os.time() - timeout) then
local db,err = ap.dbopen(r,"mod_dbd")
local _host = db:escape(r,host)
local res, err = db:query(r, ("SELECT `destination` FROM `vhosts` WHERE `hostname` = '%s' LIMIT 1"):format(_host) )
if res and #res == 1 then
cached_vhosts[host] = { updated = os.time(), destination = res[1][1] }
else
cached_vhosts[host] = { updated = os.time(), destination = nil } -- don't re-query whenever there's no result, wait a while.
end
db:close()
end
if cached_vhosts[host] then
return cached_vhosts[host].destination
else
return nil
end
end
function mass_vhost(r)
-- Check whether the hostname is in our database
local destination = query_vhosts(r)
if destination then
-- If found, rewrite and change document root
local filename = r.filename:sub(r.document_root:len()+1)
r.filename = destination .. filename
ap.set_document_root(r,destination)
return apache2.OK
end
return apache2.DECLINED
end</pre>
<p>
</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="basic_auth" id="basic_auth">Example 3: A basic authorization hook</a></h2>
<p>
With the authorization hooks, you can add custom auth phases to your request
processing, allowing you to either add new requirements that were not previously
supported by httpd, or tweaking existing ones to accommodate your needs.
</p>
<pre class="prettyprint lang-config">LuaHookAuthChecker /path/too/foo.lua check_auth</pre>
<pre class="prettyprint lang-lua">--[[
A simple authentication hook that checks a table containing usernames and
passwords of two accounts.
]]--
local accounts = {
bob = 'somePassword',
jane = 'Iloveponies'
}
-- Function for parsing the Authorization header into a username and a password
function parse_auth(str)
local user,pass = nil, nil
if str and str:len() &gt; 0 then
str = apache2.base64_decode(auth):sub(7));
user, pass = auth:match("([^:]+)%:([^:]+)")
end
return user, pass
end
-- The authentication hook
function check_auth(r)
local user, pass = parse_auth(r.headers_in['Authorization'])
local authenticated = false
if user and pass then
if accounts[user] and accounts[user] == pass then
authenticated = true
r.user = user
end
end
r.headers_out["WWW-Authenticate"] = 'Basic realm="Super secret zone"'
if not authenticated then
return 401
else
return apache2.OK
end
end</pre>
<pre class="prettyprint lang-lua">--[[
An advanced authentication checker with a database backend,
caching account entries for 1 minute
]]--
local timeout = 60 -- Set account info to be refreshed every minute
local accounts = {}
-- Function for parsing the Authorization header into a username and a password
function parse_auth(str)
local user,pass = nil, nil
if str and str:len() &gt; 0 then
str = apache2.base64_decode(auth):sub(7));
user, pass = auth:match("([^:]+)%:([^:]+)")
end
return user, pass
end
-- Function for querying the database for the account's password (stored as a salted SHA-1 hash)
function fetch_password(user)
if not accounts[user] or (accounts[user] and accounts[user].updated &lt; os.time() - timeout) then
local db = apache2.dbopen(r, "mod_dbd")
local usr = db:escape(user)
local res, err = db:query( ("SELECT `password` FROM `accounts` WHERE `user` = '%s' LIMIT 1"):format(usr) )
if res and #res == 1 then
accounts[user] = { updated = os.time(), password = res[1][1] }
else
accounts[user] = nil
end
db:close()
end
if accounts[user] then
return accounts[user].password
else
return nil
end
end
-- The authentication hook
function check_auth(r)
local user, pass = parse_auth(r.headers_in['Authorization'])
local authenticated = false
if user and pass then
pass = apache2.sha1("addSomeSalt" .. pass)
local stored_pass = fetch_password(user)
if stored_pass and pass == stored_pass then
authenticated = true
r.user = user
end
end
r.headers_out["WWW-Authenticate"] = 'Basic realm="Super secret zone"'
if not authenticated then
return 401
else
return apache2.OK
end
end</pre>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="authz" id="authz">Example 4: Authorization using LuaAuthzProvider</a></h2>
<p>
If you require even more advanced control over your authorization phases,
you can add custom authz providers to help you manage your server. The
example below shows you how you can split a single htpasswd file into
groups with different permissions:
</p>
<pre class="prettyprint lang-config">LuaAuthzProvider rights /path/to/lua/script.lua rights_handler
&lt;Directory "/www/private"&gt;
Require rights member
&lt;/Directory&gt;
&lt;Directory "/www/admin"&gt;
Require rights admin
&lt;/Directory&gt;</pre>
<pre class="prettyprint lang-lua">--[[
This script has two user groups; members and admins, and whichever
is referred to by the "Require rights" directive is checked to see
if the authenticated user belongs to this group.
]]--
local members = { "rbowen", "humbedooh", "igalic", "covener" }
local admins = { "humbedooh" }
function rights_handler(r, what)
if r.user == nil then
return apache2.AUTHZ_AUTHZ_DENIED_NO_USER
end
if what == "member" then
for k, v in pairs(members) do
if r.user == v then
return apache2.AUTHZ_GRANTED
end
end
elseif what == "admin" then
for k, v in pairs(admins) do
if r.user == v then
return apache2.AUTHZ_GRANTED
end
end
end
return apache2.AUTHZ_DENIED
end</pre>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="loadbalancing" id="loadbalancing">Example 5: A rudimentary load balancer</a></h2>
<p>
This is an example of how you can create a load balancing mechanism.
In this example, we will be setting/getting the number of requests served
by each backend using IVM variables, and preferring the backend with least
requests served in total:
</p>
<pre class="prettyprint lang-config">LuaHookTranslateName /path/to/script.lua proxy_handler</pre>
<pre class="prettyprint lang-lua">--[[
This script uses a basic IVM table to determine where to
send the request.
]]--
local backends = {
"http://backend1.foo.com/",
"http://backend2.foo.com/",
"http://backend3.foo.com/"
}
function pick_backend(r)
local chosen_backend = 1 -- default to backend1
local lowest_count = nil
for i = 1, #backends, 1 do -- Loop through all backends
local count = r:ivm_get("proxy_request_count_" .. i)
if not count then -- If this backend hasn't been used at all, prefer it
chosen_backend = i
lowest_count = 0
break
end
if not lowest_count or lowest_count &gt; count then -- If this backend has had less requests, pick it for now
chosen_backend = i
lowest_count = count
end
end
lowest_count = lowest_count + 1
r:ivm_set("proxy_request_count_" .. chosen_backend, lowest_count)
return chosen_backend
end
function proxy_handler(r)
local backend = pick_backend(r) -- Pick a backend based on no. of requests served
r.handler = "proxy-server"
r.proxyreq = apache2.PROXYREQ_REVERSE
r.filename = "proxy:" .. backends[backend] .. r.uri
return apache2.DECLINED -- let the proxy handler do this instead
end</pre>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="map_handler" id="map_handler">Example 6: Overlays using LuaMapHandler</a></h2>
<p>
Coming soon!
</p>
<pre class="prettyprint lang-config">LuaMapHandler ^/portal/([a-z]+)/ /path/to/lua/script.lua handle_$1</pre>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="mod_status_lua" id="mod_status_lua">Example 6: Basic Lua scripts</a></h2>
<p>
Also coming soon
</p>
</div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/developer/lua.html" title="English">&nbsp;en&nbsp;</a></p>
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