[brianwawok]

Thoughts as I run a similar (but completely different) setup on DO.

1) Have you considered DNS round robin for your nginx and varnish servers? Running 2 of each (at half size) would let either one die and nothing bad happen to your site.

2) Are you ok with MongoDB being a SPOF?

3) Are you okay with your main DB being a SPOF?

I ask this not to be snarky, but I see that you are 84% of the way to having a SPOF proof setup, but not quite all the way there. I know I sleep a little better at night knowing that if my nginx box blows up, I have more with DNS round robin to keep everything running till the morning.

[smusumeche]

Good suggestions! The only issue I see is that if the traffic was split between two different varnish servers, the cache would take twice as long to "warm".

[brianwawok]

Yah that is true. I would still prefer a slower to warm cache than a 1 server dies the entire app is dead, right? Depends on the app I spose.