Scaling a Web-site

On Monday we started talking about scaling web-sites to more data, more requests, and more machines to manage it all.
Today, we are going to look at Squids configured as a reverse proxy servers.
This will allow us hopefully to serve static pages as often as possible rather than having to re-compute scripts again and again.
Let's recall the web-site architecture we had from Monday...

Example Web-site Architecture

Squid

Is a caching proxy available at:
http://www.squid-cache.org/
It originally developed from Harvest Cache Daemon project at UCSD. The latter project started in the 1990s.
We are interested in using squids as a reverse proxies: The idea is clients (browsers), connect to our site and hit our squid, the squid determines if it already has a non-expired copy of the page requested in its cache, if it does, it returns it; otherwise, it forwards the request to one of a collection of webservers who runs the requested script. The returned result in this second case is then cached in the squid.

Setting up squid

We first need to download and compile the squid src's. (./configure; make; sudo make install)
Next we need to edit the squid.conf file in the squid ${squid}/etc/squid.conf
Then one can type the command:
```
/usr/local/squid/sbin/squid -z
```
This just makes the cache directories (${squid}/var/cache/hex_number), if you don't already have them .
Then one can run squid with:
```
/usr/local/squid/sbin/squid -NCd1 #for debugging
```
without -NCd1 if don't want debugging.

Testing Squid

To just test out squid, we will set it up first as a proxy cache.
The idea of a proxy cache is we want a cache for our LAN of any websites off of the LAN.
The squid.conf has the ability to finely control which requests through it will be allowed.
You can set up acl (access control lists). The default acl in squid.conf looks like:
```
acl localhost src 127.0.0.1/32
```
We next say what http stuff localhost is allowed to do by adding the following directive:
```
http_access allow localhost 
```
Next you can start your squid server, and either request web pages using the squidclient or set up a proxy of localhost and port 3128 in your browser.

For example:

${squid}/bin/squidclient http://pollett.org/
HTTP/1.0 200 OK
Date: Wed, 24 Nov 2010 20:57:21 GMT
Server: Apache/2.2.15 (Unix) mod_ssl/2.2.15 OpenSSL/0.9.8l DAV/2 PHP/5.3.3 SVN/1.6.5
X-Powered-By: PHP/5.3.3
Cache-Control: max-age=60
Expires: Wed, 24 Nov 2010 20:58:21 GMT
MS-Author-Via: DAV
Content-Length: 2231
Content-Type: text/html
X-Cache: MISS from chris-polletts-macbook-pro.local
Via: 1.0 chris-polletts-macbook-pro.local (squid/3.0.STABLE10)
Proxy-Connection: close

<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
...

Notice in the above we had a cache miss.
To see the actual cache hits and misses you can look in ${squid}/var/logs/access.log
In Firefox to Configure the proxy server for to Preferences::Advaced::Network::Connection::Settings. Do manual proxy settings, use localhost as the host and 3128 as the port.

Configuring Squid as a Reverse Proxy

To match the sample website architecture we want the squid to be on the main machine people come into our website at.
Then we want it to cache pages that will be coming from our web servers.

We need to edit the lines:

http_port (probably set to port 80 from default 3128)
httpd_accel_host (set to virtual if have more than one web server; otherwise, to ip address of the web server)
httpd_accel_port (port number of web servers 80)
httpd_accel_single_host ( on or off depending on how many webservers you have,)
httpd_accel_uses_host_header off

Load Balancing Machines

You can also set up squid to do the load balancing between your web servers using directives like:

cache_peer ip.of.server1 parent 80 0 no-query round-robin
acl sites_server_1 dstdomain www.mysite.com
http_access allow sites_server_1

cache_peer ip.of.server2 parent 80 0 no-query round-robin
acl sites_server_2 dstdomain www.mysite.com
http_access allow sites_server_2

Flash

Flash was originally a product to make it easy to produce vector based animations on the web created around 1996 based on technology purchased by Macromedia (now Adobe) from Futurewave.
Flash programs are typically executed by the Flash player plug-in which is (as of 2009) available in some browser on 99% of desktops .
It is used to create Rich Internet Applications (RIA) and competes against HTML 5, AJAX, Silverlight (Windows), Applets (Java), etc.
It can also be used to do tracking (Local Shared Objects/ Persistent Identification Elements (PIE) -- not turned off as often as easily as cookies)
It has the advantage over AJAX that as the plug-in is produced by one source, it runs the same in any browser. It also supports richer kinds of media like Video. (YouTube).
HTml 5 might eventually do the things that Flash allows; however, there are still issues surrounding video playback in Html 5.

Flex

The main authoring tool for Flash is Flash Professional, which is GUI IDE designed to make it easy to create Flash.
Flex is an Adobe product which gives a more programmatic way to create Flash files.
There is a Flex IDE, Flex Builder, which can also be used, however, the basic SDK is open sourced under the Mozilla License (can mix proprietary and open source code).
We will only look at the basic SDK which we will access mainly from the command line.
There are other open-source tool chains which can be used to create .swf files, notably, OpenLaszlo.

Adobe Air

Air is a product released by Adobe in Feb, 2008 to make it easy to convert Flash programs into stand-alone applications.
Since Flash is cross-platform, these apps are as well, and it makes it relatively easy to write code which will work on PCs, Mac's, and Linux.
Air apps can do more things than Web Flash apps. For instance, you can access the file system, drag and drop from the OS to your app, etc.

Installation

Currently (Nov 2010), the release version of Flex is Flex 4.
It can be found at:
http://www.adobe.com/products/flex/flexdownloads/.
Download this file and unzip it somewhere you know, say C:\FlexSDK (Windows) or /usr/local/flex(*nix including Mac)
Then add C:\FlexSDK\bin or /usr/local/flex/bin to your PATH variable (use control panel Windows, or edit .profile, .cshrc, etc on *nix).
Restart your shell.
The programs to compile AIR apps come with Flex 4; however, to test it you still need the AIR runtime:
http://get.adobe.com/air/.

Squid, Start Flex

Outline

Scaling a Web-site

Example Web-site Architecture

Squid

Setting up squid

Testing Squid

Configuring Squid as a Reverse Proxy

Load Balancing Machines

Flash

Flex

Adobe Air

Installation