Scaling Apache for LAMP

Buddhika Siddhisena

(Co-Founder & CTO of THINKCube Systems)

bud@thinkcube.com | twitter @geekaholic

What is ApacheThe folk story is that Apache was named after "A-patchy-server", which was the result of NCSA httpdserver being patched a lot. The project was started by Brian Behlendorf

Today, Apache is still the most popular web server out there running more than half of the websiteson the net. It is actively developed by the Apache Software Foundation along with many other softwareprojects.

Besides its primary function of being a website, Apache can also be configured as a reverse proxy forload balancing.

Installing ApacheThe easiest method of installing Apache along with PHP and MySQL (aka LAMP) is to use the taskselcommand.

tasksel

Alternatively install each package manually:

apt-get install apache2 libapache2-mod-php5 mysql-server

Installing a sample LAMP app - Drupal

In order to test out Apache performance as we tune it, it is good to setup a real world full fledged CMSsuch as Drupal.

Download the latest version of Drupal from drupal.org

Follow the Drupl setup guide

Install the Devel module into Drupal modules directory

Login to Drupal as admin and using the devel plugin, populate Drupal with sample data for testing(Configuration -> Development -> Generate Content)

Setting up Benchmarking tools

Setup Autobench

Autobench is a handy script to stress test a webserver by sending an increasing number of requests. Itworks by calling the httperf tool iteratively with increasing parameters.

Download autobench and follow directions to compile.

In order to plot graphs, you need to install gnuplot via apt. As of this writing, the script used to plotthe graph has a bug calling the current version of gnuplot and requires the following minormodification.

$ sudo vi which bench2graph

line ~78 should be

echo set style data linespoints >> gnuplot.cmd

Baseline benchmark with AutobenchLets benchmark our standard Apache setup to get an idea of default performance.

autobench --single_host --host1 localhost --uri1 /drupal --quiet \ --low_rate 20 --high_rate 200 --rate_step 20 --num_call 10 \ --num_conn 5000 --timeout 5 --file results.tsv

Basically the above will test a single host, localhost/drupal by sending it 20 connections per second,each having 10 requests up to 200 connections per second incrementing by 20. The total number ofconnections are capped at 5000 while any request that takes more than 5 seconds to respond isconsidered unsuccessful.

Plotting the results

Using the result.tsv file and the included bench2graph utility, you can plot a graph into a postscriptfile.

bench2graph results.tsv results.ps

Tuning Apache - Enable GZipYou can decrease network overhead and make pages load faster, there by reducing the amount oftime a client is connected by compressing pages using gzip. All modern browser support renderingcompressed files.

In order to benchmark its effect, you can install a tool such as Firebug on the client side.

Tuning Apache - Enable GZipEnable the mod_deflate module. On Ubuntu :

a2enmod deflate && a2enmod headers

Then we'll configure deflate to compress everything except images.

sudo vi /etc/apache2/modules-enabled/deflate.conf

1 <Location /> 2 # Insert filter 3 SetOutputFilter DEFLATE 4 5 # Don't compress images 6 SetEnvIfNoCase Request_URI .(?:gif|jpe?g|png)$ no-gzip dont-vary 7 8 # Make sure proxies don't deliver the wrong content 9 Header append Vary User-Agent env=!dont-vary10 11 </Location>

Apache configuration tuningThere are a few key parameters that can be tuned:

KeepAlive - By default its set to ON which is good. Clients will make all requests in one shot viahttp 1.1.

KeepAliveTimeout - Better to keep it low. Defaults to 15 sec. Make sure thats enough. Rule is 1.5to 2 times your page load speed.

TimeOut - The default is 5 minutes which might be long to allow for one process. Adjustaccordingly.

StartServers, MinSpareServers, MaxSpareServers - Generally even on a busy site you may not needto tweak. Apache can self regulate.

MaxClients - The maximum number of clients (threads) Apache will handle simultaneously.

Calculating MaxClients

ps -eafly |grep apache2|awk '{print $8}'|sort -n

Use free to figure out how much memory is available. Cache is also considered free memory but youmight want to leave some and not assume all cache will be used.

free

By deviding free memory by the average memory used by an Apache thread, you can estimate thenumber of MaxClients.

e.g: Assuming Apache memory usage and free memory are as follows

$ ps -eafly |grep apache2|awk '{print $8}'|sort -n

816389638963896389620844

$ free total used free shared buffers cachedMem: 508904 447344 61560 0 141136 213468-/+ buffers/cache: 92740 416164Swap: 407544 4364 403180

Memory avail ~= 60000 (free) + 100000 (cached) ~= 160 MB and Memory per thread ~= 4 MB Then asafe value for MaxClients = 40

Improving PHP performanceWe can improve PHP performance by

1. Caching pages (useful if dynamic content doesn't change often)

2. PHP Opcode optimizations (pre-compile php)

Fortunately we can get the benefit of both using PHP APC, which is a PHP accellerator!

apt-get install php-apc

You can verify installation by loading a php page having phpinfo(); and searching for apc. Or if youhave php5-cli installed:

php -r "phpinfo();" | grep apc

Using memcached

Memcached is a distributed cache for storing key-value pairs in memory for faster access withreduced trips to the database. Some popular PHP apps can use memcache if available. memcacheddoes not instantly accellerate PHP!

apt-get install memcached php5-memcache

service memcached start

More Tips for improving performanceKeep DirectoryIndex file list as short as possible.

Whenever possible disable .htaccess via AllowOverride none

Use Options FollowSymLinks to simplify file access process in Apache

Minimize the use of mod_rewrite or at least complex regexs

If logs are unnecessary disable them or log to another server via syslog.

For Deny/Allow rules use IPs rather then domains. (prevents superfluous DNS lookups).

Do not enable HostnameLookups (DNS is slow).

For dynamic sites see if you can separate dynamic vs static content into two servers

Scaling Architectures

Buddhika Siddhisena

(Co-Founder & CTO of THINKCube Systems)

bud@thinkcube.com | twitter @geekaholic

Architecture overviewIn terms of scaling the web server there are few options.

1. Single machine (Scale vertically)

Basically the easiest to setup. Scaling is a matter of buying a better server or upgrading it!

2. App-DB machines (2-Tier)

Separate DB from App, as a result each can be scaled separately.

Architecture overview contd...

3. Load balancer + App-DB machines (3-Tier)

Load balancer (aka reverse proxy) will route requests betwen multiple backend HTTP servers whilecaching results.

Data IndependenceIt is good to isolate the data from the app by hosting it on a separate server. This was the two aspectscan be scaled independantly. Some methods to consider:

Store DB data on MYSQL running on a separate server

Enable file sharing to share data files using NFS, rsync

Clustering MYSQL across multiple servers using mysqlcluster

Cluster file system via DRDB, GFS2 or as Facebook does using Bittorrent

Setting up an HTTP accelleratorusing Apache

Apache as a reverse proxyIn this setup, the reverse server is what the user will contact while the real webserver can be hiddenbehind a private network.

1. On the reverse proxy server :

Enable required modules for caching reverse proxy.

a2enmod proxy

a2enmod proxy_connect

a2enmod proxy_http

a2enmod cache

2. Configure proxy module

vi /etc/apache2/modules-enabled/proxy.conf

1 <Proxy *>2 AddDefaultCharset off3 Order deny,allow4 Deny from all5 Allow from all6 </Proxy>7 ProxyVia On

Apache as a reverse proxy contd...

3. Setup (public) virtual host

Next we configure an empty virtual host that is configured to the public site. But instead of showingthe document root we do a reverse proxy.

vi /etc/apache2/sites-available/public-domain.com

1 <VirtualHost *:80> 2 3 ServerName your-public-domain.com 4 5 <Proxy *> 6 Order deny,allow 7 Allow from all 8 </Proxy> 9 10 ProxyPass / http://your-private-domain.com/11 ProxyPassReverse / http://your-private-domain.com/12 13 </VirtualHost>

a2ensite public-domain.com service apache2 reload

Using Nginx

What is Nginx?

Nginx was designed as a reverse proxy first, and an HTTP server second

Unlike Apache, Nginx uses a non blocking process model

Two modes of operation for Nginx:

1. Use Nginx for the static content and Apache for PHP

2. Use FastCGI to embed PHP

Nginx process model in a nutshellReceive request, trigger events in a process

The process handles all the events and returns the output

Process handles events in parallel

Limitation is PHP can no longer be embedded (mod_php ) inside process as PHP is not asynchronous

Unlike Apache, Nginx doesn't not have an .htaccess equivelant. You need to reload server aftermaking any chage, making it difficult to use for shared hosting

Using Nginx and Apache side-by-sideIn this setup we put Nginx as the frontend http accellerator and Apache as the backend app server. Ifyou want to run this on the same physical server you'll need to either change the Apache port from 80to another value or bind and Nginx to their own IP addresses with the same server.

Listen 8080

or using the ip address

Listen 127.0.0.1:8080

Now we're ready to install Nginx

sudo apt-get install nginx

Apache style virtual host in Nginx

Nginx uses a different format for defining virtual hosts than Apahche.

1 <VirtualHost>2 DocumentRoot "/usr/local/www/mydomain.com"3 ServerName mydomain.com4 ServerAlias www.mydomain.com5 CustomLog /var/log/httpd/mydomain_access.log common6 ErrorLog /var/log/httpd/mydomain_error.log7 ...8 </VirtualHost>

becomes...

1 server { 2 root /usr/local/www/mydomain.com; 3 server_name mydomain.com www.mydomain.com; 4 5 # by default logs are stored in nginx's log folder 6 # it can be changed to a full path such as /var/log/... 7 access_log logs/mydomain_access.log; 8 error_log logs/mydomain_error.log; 9 ...10 }

Redirecting all PHP requests to Apache

The following example will server all static content via nginx while redirect dynamic content (php) toApache

1 server { 2 listen 80 default; 3 server_name localhost; 4 5 access_log /var/log/nginx/localhost.access.log; 6 7 location / { 8 root /var/www; 9 index index.html index.htm;10 }11 12 ## Parse all .php file in the /var/www directory13 location ~ .php$ {14 # these two lines tell Apache the actual IP of the client being forwarded15 16 proxy_set_header X-Real-IP $remote_addr;17 proxy_set_header X-Forwarded-For $remote_addr;18 19 # this next line adds the Host header so that apache knows which vHost to serve20 21 proxy_set_header Host $host;22 23 # And now we pass back to apache24 proxy_pass http://127.0.0.1:8080;25 26 }27 }

ReferencesHow To Improve Website Performance (With Drupal, LAMP)

PHP Performance tuning

HipHop compiler by Facebook

How the code you write affects PHP benchmarks

Scaling Facebook with OpenSource tools

Scaling drupal

DRBD for HA distributed file system

Thank you

bud@thinkcube.com | twitter @geekaholic