Optimize High Traffic WordPress Website – Best Practices

The key to surviving a massive influx in traffic is to increase the amount of concurrent requests you can handle, that means a)decrease the time it takes to render pages so you can serve more visitors quickly, or b)get a hosting platform that is capable of handling more connections.

If you expect lots of media traffic, shared hosting is not for you. At the least you should temporarily upgrade to a VPS or dedicated server - this is a critical time for your business (and you) and you don't want website and email trouble.

If you're short on time, I wouldn't recommend moving to something like cloud - you're not going to be horizontally scaling much as far as know (but I've almost no experience on that - I might be wrong). You'd also potentially have to go through changing DNS and changing hosts - which can be a traumatic experience depending on support teams on both sides. See if godaddy can you up to a dedicated server - this would provide you dedicated CPU time and ram and get you out of an environment where you're potentially going to be shut off for affecting other users. You might only be on this plan for a month or two - then you can make a decision if moving back to shared hosting is right for you.

If you have time to move a copy of your site to a dedicated server before re-pointing the DNS, you should see if you can benchmark that copy of your site before it goes live to see if you need further optimization or if throwing cash at it was enough. You can with something like apache ab if you have access to a linux machine (or can grab a cheap linux vps) - a quick guide on this can be found here: http://www.cyberciti.biz/tips/howto-performance-benchmarks-a-web-server.html

As to other optimizations, SQL server is probably faster than access, and could probably be setup on your dedicated machine or a VPS. You'll want to get the site developers involved and see if they can implement any caching or if they can make any database optimizations, as those will lower the time it takes to render a page and move onto the next visitor.

There are many things it could be but start with the most likely things with an Apache/PHP server:

1. Memory -- If Apache is misconfigured it will eat up all the RAM and begin to use swap space which will kill your performance. Check to make sure your swap space is not used (or not used much). If it is reduce Apache's MaxClients or the memory consumption of whatever else is running on the server (MySQL, etc...). Since you say it is only using half then this may not be the problem, although 800 Apache processes in 4GB is only 5MB/process seems very low.
2. CPU -- PHP can be very CPU intensive, especially combined with other application/database. Check your server load and CPU usage in top to see how much you're using. Using a simple monitoring program like sar, or a more complex one like Nagios or Zabbix, can give you more detail on the CPU load over time. The one main thing you can do here is to install and use a PHP opcode cache like APC or eAccelerator. After that there is typically not much else you can do other than optimizing your database/application.
3. IO -- Check the output of top and iostat to see how much IO you are doing. A high wa% in top, either intermittent or constant, usually indicates an IO issue. If it is an IO issue then find out where it is occurring (Apache, PHP, database, something else, etc...) as the solution will ultimately depend on what is causing it.

I would also check the various log files for any obvious error messages (system, Apache, database, etc...). I know I've had sites with performance issues only because of something like the number of file handles was set too low for a high volume web site.