An interesting issue, though somewhat aggravating as this is happening to a live and active website.
=> Every morning around 8am, our website goes down with a 502 Bad Gateway Error. It's almost on the dot in Google Analytics. There are no major traffic spikes around this time, we have traffic around the clock.
=> The website uses 140-180mb of 'real' memory, the rest is cache. What I did notice is that cache slowly creeps up before these times and gets pretty close to the limit set for the VPS. I've upped the VPS by 50mb each morning this happened, but the issue keeps returning. It could be this, but I am not 100% sure.
We're running Nginx with PHP 5.4.20. We've got some custom settings in terms of browser caching, etc.
The website itself uses the Wordpress platform and is fully up-to-date. When it runs, I am more than happy with the speed.
Any thoughts, suggestions, comments are highly appreciated.
For those interested, the website can be found here: www.manapool.co.uk
Our old design was DHSOTM in 2010.