I have followed the steps for resizing an EC2 volume
Bootable flag (a) didn't worked in my case (EC2, centos6.5), so i had to re-create volume from snapshot. After repeating all steps EXCEPT bootable flag - everything worked flawlessly so i was able to resize2fs after. Thank you!
Prefect comment by jperelli above.
I faced same issue today. AWS documentation does not clearly mention growpart. I figured out the hard way and indeed the two commands worked perfectly on M4.large & M4.xlarge with Ubuntu
sudo growpart /dev/xvda 1
sudo resize2fs /dev/xvda1