If you are running Ubuntu Trusty 14.04 and both of the following commands return output:

mount | grep ext3
sudo tune2fs -l /dev/xvda1 | grep RAID

Then if your systems boots using linux-image-3.13.0-157-generic, the file system will almost immediately remount read-only. To prevent this, manually select an older kernel or run the following:

sudo apt-get install linux-image-virtual-lts-xenial

To install a kernel series without this bug. We filed a bug upstream.