Linux System Administration

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Chapter 7: Load-Balanced Clusters

Scaling Without LB and HA

If you offered a wonderful service, would your server survive a Slashdotting (i.e., a

huge activity spike)? If not, your credibility could suffer and many visitors might

never return. But because implementing LB and HA requires significant effort and

hardware investments, it’s worth considering other solutions. There are ways to get

more from your present server. For instance, you can disable .htaccess files in your

Apache configuration (

AllowOverride None), and use mod_expires to avoid stat calls

for infrequently changed files such as images. Apache books and web sites contain

many such optimization tips.

Once you reach the limits of your web server software, consider alternatives. In many

cases, web servers such as lighttpd (http://www.lighttpd.net), Zeus (http://www.

zeustech.net), and litespeed (http://litespeedtech.com) are faster than Apache and use

less memory.

You can also get huge boosts from caching. Code caches, which include PHP acceler-

ators such as e-accelerator (http://eaccelerator.net) and APC (http://apc.

communityconnect.com), save PHP bytecode and avoid parsing overhead on each

page access. Data caches such as MySQL’s query cache save the results of identical

queries. Replication is a form of LB. memcached (http://danga.com/memcached)isa

fast way to cache data such as database lookup results. Squid (http://www.squid- ...