I just had a look at my Amazon EC2 instance and noticed I had 20 minutes exactly of downtime. I didn't know what caused it so I logged in to SSH and tried upgrading my packages, and saw that the
unattended-upgrades package needed upgrading. I went ahead and did this.
After searching it seems like this package can automatically reboot your machine. Not sure why I didn't get to configure this as it came with the OS, but oh well.
Does anyone know how to prevent the package from automatically rebooting? Or how to stop it updating packages altogether? I can do that myself.