How to online grow a ext4 partition

This tutorial uses Arch Linux so package names might vary

1. Install cloud-guest-utils which includes growpart
2. Backup your partition table so you can recover if needed
   sudo sfdisk -d /dev/sda > partition_bak.dmp
3. Use growpart to grow the partition
   growpart /dev/sda 2
4. Use resize2fs to grow your filesystem
   resize2fs /dev/sda2

Now you should have a ext4 partition that spans the entire rest of your drive.