What's the best php/mysql/apache configuration for the $10/mo, $20/mo plan droplet?

If you’re seeing services crash under high load there is a good chance your droplet is exhausting it’s available memory. The first thing I would recommend is to set up a swap file.

This should help prevent the crashes as a service would not simply run out of memory when the physical RAM is all in use. Instead of a crash you may see some slowdown in responses since your system would be swapping out memory to disk rather than simply crashing. This is a good stop-gap but you would then want to dig into things to see what you can further optimize or whether you need to upgrade to a larger droplet.

Another thing that may provide some relief to your server is to set up CloudFlare’s reverse proxy service for your domain. This provides a cache between your droplet and your users and can significantly reduce the load on your droplet, especially when you are seeing a lot of visitors.

If your site has a lot of database queries you might consider memcached (if mysql is crashing) I recently had an issue with Joomla running a custom application that was very database intensive and memcached solved things…although I already had a swap partition as well.