This package is intended to expand the root partition up to 2TB on a GCE VM. It consists of several scripts from other packages that for various reasons are not maintained by the distros; cloud-utils-growpart, dracut-modules-growroot, and an upstream version of the growpart script. See below for details. This package is included in GCE CentOS and RHEL images after v20160415.
A script to build the package is provided for convenience. ./build_package.sh /OUTPUT_DIR will yield an rpm and an srpm in the defined output directory for EL6 and EL7.
Install the gce-disk-expand package for your distro with yum and reboot:
CentOS/RHEL 6: yum -y install /PATH_TO/gce-disk-expand-el6-VER-DATE.x86_64.rpm ; reboot
CentOS/RHEL 7: yum -y install /PATH_TO/gce-disk-expand-el7-VER-DATE.x86_64.rpm ; reboot
Your root partition will now be expanded to the full size of your disk up to 2TB.
The growpart script used in this package is not from the 0.27 cloud-utils-growpart package. There are bugs in that version of growpart, primarily a bug that doesn't respect 2TB disk partitions on MBR disks. This means that if you had a disk that was 2.1TB, you would end up with a 0.1TB partition instead of 2TB partition. Obviously, this is bad. The upstream cloud-utils 257 release fixes this bug and others while not introducing more bugs and dependencies in further upstream releases of this script. It is therefore not recommended that you try to use the 0.27 growpart package from the EPEL repo.
The dracut module is taken from the dracut-modules-growroot package in the EPEL 6 repo. The dracut module allows the partition table to be expanded on boot before / is mounted and prevents an additional reboot in CentOS and RHEL 6. CentOS and RHEL 7 support live partition resizing by the kernel and do not need the dracut module.
The expand-root script is derived from the bootstrap-vz version of this script used for Debian instances. Essentially, it just calls the proper filesystem expansion utility to live resize the filesystem on first boot. The root partition is hard coded as /dev/sda1 in this script.