For what it is worth, DO NOT, I REPEAT, NOT DO NOT USE FDISK to resize your partition!
To quickly resize your EBS elastic volume, I will perform this task on a Ubuntu 18 EC2 instance.
lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 89.1M 1 loop /snap/core/8039
loop1 7:1 0 18M 1 loop /snap/amazon-ssm-agent/1480
loop2 7:2 0 89.1M 1 loop /snap/core/7917
xvda 202:0 0 15G 0 disk
└─xvda1 202:1 0 8G 0 part /
# install "cloud-guest-utils" if it is not installed already
sudo apt install cloud-guest-utils
# resize partition
sudo growpart /dev/xvda 1
CHANGED: partition=1 start=2048 old: size=16775135 end=16777183 new: size=31455199,end=31457247
lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 89.1M 1 loop /snap/core/8039
loop1 7:1 0 18M 1 loop /snap/amazon-ssm-agent/1480
loop2 7:2 0 89.1M 1 loop /snap/core/7917
xvda 202:0 0 15G 0 disk
└─xvda1 202:1 0 15G 0 part /
# Check before resizing ("Avail" shows 1.1G):
df -h
Filesystem Size Used Avail Use% Mounted on
udev 481M 0 481M 0% /dev
tmpfs 99M 908K 98M 1% /run
/dev/xvda1 7.7G 6.7G 1.1G 87% /
tmpfs 492M 0 492M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 492M 0 492M 0% /sys/fs/cgroup
/dev/loop0 90M 90M 0 100% /snap/core/8039
/dev/loop1 18M 18M 0 100% /snap/amazon-ssm-agent/1480
/dev/loop2 90M 90M 0 100% /snap/core/7917
tmpfs 99M 0 99M 0% /run/user/1000
# resize filesystem
sudo resize2fs /dev/xvda1
resize2fs 1.44.1 (24-Mar-2018)
Filesystem at /dev/xvda1 is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 2
The filesystem on /dev/xvda1 is now 3931899 (4k) blocks long.
# Check after resizing ("Avail" now shows 8.7G!-):
df -h
Filesystem Size Used Avail Use% Mounted on
udev 481M 0 481M 0% /dev
tmpfs 99M 908K 98M 1% /run
/dev/xvda1 15G 6.7G 7.8G 47% /
tmpfs 492M 0 492M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 492M 0 492M 0% /sys/fs/cgroup
/dev/loop0 90M 90M 0 100% /snap/core/8039
/dev/loop1 18M 18M 0 100% /snap/amazon-ssm-agent/1480
/dev/loop2 90M 90M 0 100% /snap/core/7917
tmpfs 99M 0 99M 0% /run/user/1000