speeding up your nginx server with memcached

Nginx is a high performance web and proxy (web and mail proxy) server. Generally, nginx is used as a front-end proxy server to Apache webserver. Nginx is known to be slow while serving dynamic pages like php. Normally, nginx is using fast-cgi method which is slow. Therefore, it's a good idea to run Apache as back-end server to Nginx and serve dynamic php pages from Apache. If your website's php pages suitable to cache for a certain time, you can use Nginx proxy module and proxy_store command to cache Apache served php pages output in Nginx automatically as html. Here, I'll give you instructions how to use Nginx's memcache module and Danga Software's memcached deamon to store your content in memory and serve it. Serving content from memory will be faster than serving it from disk. memcached's default listening port is 11211. You can find instructions on Danga Software's website how to compile and run memcached.

Now, we can look our Nginx configuration for memcache implementation. Let's suppose we have two Apache webservers running on two different physical servers. IP addresses of the Apache webservers are 192.168.2.3 and 192.168.2.4. We'll use those Apache webservers as back-end servers. We have a Nginx server as front-end to them on 192.168.2.1 ip adress. First of all, we have to tell Nginx about those back-end servers. We use Nginx upstream module for this purpose. As you can see below, we defined a upstream named "backend". The configuration has our two Apache webservers ip addresses. Upstream module let's you also give weight to each server in configuration. Our first server's hardware configuration is better than the second one, so we gave the first one weight value 2. This configuration should be in http section of Nginx configration file (nginx.conf).

upstream backend {
     server 192.168.2.3 weight=2;
     server 192.168.2.4;
}

We have created our upstream configuration. Now, we have to tell Nginx, which files will be server by memcache module. I have decided to only serve some image types by memcache. The following configuration part should be in server section of Nginx configuration. The "location" directive tell's the nginx to handle every file which ends with given extensions like .jpg,.png and .gif in url. As first step, Nginx will check the url in memcached. Memcached is simple key value memory database. Every row has a unique key.In our case the key is our url. If Nginx, finds the key (url) in memcached, it will get contents of the key from mecached and send it back to client. This operation is running completely from memory. In case that the key (url) not found, it will fallback to 404 and as you can see, we catch 404 error and send request to our back-end Apache servers. Nginx will then send Apache's response to client.

location ~* \.(jpg|png|gif)$ {
access_log   off;
expires      max;
add_header   Last-Modified "Thu, 26 Mar 2000 17:35:45 GMT";
set $memcached_key $uri;
memcached_pass     127.0.0.1:11211;
error_page         404 = /fetch;
}

location /fetch {
internal;
access_log   off;
expires      max;
add_header   Last-Modified "Thu, 26 Mar 2000 17:35:45 GMT";
proxy_pass http://backend;
break;
}

Of course, we have a drawback here. Nginx's memcache module never put anything automatically in memcached. You have to store your information in it manually by using something like a script. Considering our example, if we forget to store information about a file in memcached, it will be always served by back-end Apache servers. Here is a simple php script, which finds given image types and deploy it into memcached for Nginx.

<?php

function rscandir($base='', &$data=array()) {
$array = array_diff(scandir($base), array('.', '..'));

foreach($array as $value) :
  if (is_dir($base.$value)) {
    $data = rscandir($base.$value.'/', $data);

  }
  elseif (is_file($base.$value)) {
   $rest = substr($value, -4);
   if ((!strcmp($rest,'.jpg')) || (!strcmp($rest,'.png'))
                                || (!strcmp($rest,'.gif')) ){
         $data[] = $base.$value;
   }
 }

endforeach;
return $data;
}

$mylist=rscandir("/var/www/mysite");

$srch = array('/var/www/mysite');
$newval = array('');

$memcache_obj = memcache_connect("192.168.2.1", 11211);

while (list($key, $val) = each($mylist)) {
  $url=str_replace($srch,$newval,$val);
  echo "$key => $val -> ".filesize($val)."\n";
  $value = file_get_contents($val);
  memcache_add($memcache_obj, $url, $value, false, 0);
}
?>

You need to run this script one time, it will find all given image types and store them into memcached. I run this on one of the Apache back-end servers. It will store data into memcached. This memcached is located on Nginx server which ip address is 192.168.2.1 .