Mongo replication set. Hopeful future feature.
I have read the replication blog post from 2 years ago and have had little success of getting them to actually work.
*Does DigitalOcean plan to allow do a cluster one click install? Choose number of nodes and server type and they create a replication set would be ideal. (something similar to Google's cloud services) *
Or at least someone have a better write up on how to complete process.