Digital Ocean is a great service, but by default no swap file is set on their droplets.

I first realised this issue when my droplet was killing my composer update process. This can lead you to thinking you need a more powerful Droplet, but simply enabling a swap file will overcome this memory issue. I will link to a guide on their server as it worked for me, and hope it doesn’t break: How To Add Swap Space on Ubuntu 16.04