I want to see if someone else is having this problem. I have tried this 3 times in the last two days everytime i run into same problem.
I create micro instance with CentOS 7.1.1503 image. I SSH into it, switch to root (sudo su) and just run
yum -y update
The process always starts proceeding and ultimately it hangs (100% CPU) to where the screen stops refreshing and you can not create a new SSH session to your instance. I waited patiently for 6 hours before killing my instance all 3 times.
I do the same with CentOS 6.7, updates is all OK and completes successfully.