Adding SWAP to AWS EC2 Instance

[root@ip-172-31-8-223 /]# more /etc/fstab

#
# /etc/fstab
# Created by anaconda on Mon Nov  9 20:20:10 2015
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=379de64d-ea11-4f5b-ae6a-0aa50ff7b24d /                       xfs     defaults        0 0
/dev/xvdf                                 /opt/IBMDocker                  btrfs   defaults        0 0
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# more /etc/mnttab
/etc/mnttab: No such file or directory
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# lsblk
NAME                                                                                  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
xvda                                                                                  202:0    0   10G  0 disk
├─xvda1                                                                               202:1    0    1M  0 part
└─xvda2                                                                               202:2    0   10G  0 part /
xvdf                                                                                  202:80   0  150G  0 disk /opt/IBMDocker
xvdg                                                                                  202:96   0   20G  0 disk
loop0                                                                                   7:0    0  100G  0 loop
└─docker-0:36-3241-pool                                                               253:0    0  100G  0 dm
  ├─docker-0:36-3241-d54f81e9015ddc70c47a99fa8f2b682cbddde4a2bf8544e346447eb013adbcdc 253:1    0   50G  0 dm
  ├─docker-0:36-3241-3c373a7b8bc9c4a2d22e4c6d82ff112d22679dc226834175f4b7a0fc71eec85b 253:2    0   50G  0 dm
  ├─docker-0:36-3241-5ac5006fbca47bcedcfe9c3140cfbfa96b739d1e1a943287607915cd20b8011c 253:3    0   50G  0 dm
  ├─docker-0:36-3241-eaa5b76f2e987165319fb006d1850f7283d9071f01175f17da3d05126fbb7423 253:4    0   50G  0 dm
  ├─docker-0:36-3241-6bf3bda9ecc67ad639fb127bcdd91610b2dfb3b7b8c8479494bad342fb34c801 253:5    0   50G  0 dm
  └─docker-0:36-3241-3149fd173c6a79bfcd1dfb0c94d07a77caf3e1bd605106b0f8ad9affcae29ef3 253:6    0   50G  0 dm
loop1                                                                                   7:1    0    2G  0 loop
└─docker-0:36-3241-pool                                                               253:0    0  100G  0 dm
  ├─docker-0:36-3241-d54f81e9015ddc70c47a99fa8f2b682cbddde4a2bf8544e346447eb013adbcdc 253:1    0   50G  0 dm
  ├─docker-0:36-3241-3c373a7b8bc9c4a2d22e4c6d82ff112d22679dc226834175f4b7a0fc71eec85b 253:2    0   50G  0 dm
  ├─docker-0:36-3241-5ac5006fbca47bcedcfe9c3140cfbfa96b739d1e1a943287607915cd20b8011c 253:3    0   50G  0 dm
  ├─docker-0:36-3241-eaa5b76f2e987165319fb006d1850f7283d9071f01175f17da3d05126fbb7423 253:4    0   50G  0 dm
  ├─docker-0:36-3241-6bf3bda9ecc67ad639fb127bcdd91610b2dfb3b7b8c8479494bad342fb34c801 253:5    0   50G  0 dm
  └─docker-0:36-3241-3149fd173c6a79bfcd1dfb0c94d07a77caf3e1bd605106b0f8ad9affcae29ef3 253:6    0   50G  0 dm
[root@ip-172-31-8-223 /]# mkswap -f /dev/xvdg
Setting up swapspace version 1, size = 20971516 KiB
no label, UUID=e322f4a9-cfdb-4906-9c45-74362ba4fac6
[root@ip-172-31-8-223 /]# swapon /dev/xvdg
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# lsblk
NAME                                                                                  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
xvda                                                                                  202:0    0   10G  0 disk
├─xvda1                                                                               202:1    0    1M  0 part
└─xvda2                                                                               202:2    0   10G  0 part /
xvdf                                                                                  202:80   0  150G  0 disk /opt/IBMDocker
xvdg                                                                                  202:96   0   20G  0 disk [SWAP]
loop0                                                                                   7:0    0  100G  0 loop
└─docker-0:36-3241-pool                                                               253:0    0  100G  0 dm
  ├─docker-0:36-3241-d54f81e9015ddc70c47a99fa8f2b682cbddde4a2bf8544e346447eb013adbcdc 253:1    0   50G  0 dm
  ├─docker-0:36-3241-3c373a7b8bc9c4a2d22e4c6d82ff112d22679dc226834175f4b7a0fc71eec85b 253:2    0   50G  0 dm
  ├─docker-0:36-3241-5ac5006fbca47bcedcfe9c3140cfbfa96b739d1e1a943287607915cd20b8011c 253:3    0   50G  0 dm
  ├─docker-0:36-3241-eaa5b76f2e987165319fb006d1850f7283d9071f01175f17da3d05126fbb7423 253:4    0   50G  0 dm
  ├─docker-0:36-3241-6bf3bda9ecc67ad639fb127bcdd91610b2dfb3b7b8c8479494bad342fb34c801 253:5    0   50G  0 dm
  └─docker-0:36-3241-3149fd173c6a79bfcd1dfb0c94d07a77caf3e1bd605106b0f8ad9affcae29ef3 253:6    0   50G  0 dm
loop1                                                                                   7:1    0    2G  0 loop
└─docker-0:36-3241-pool                                                               253:0    0  100G  0 dm
  ├─docker-0:36-3241-d54f81e9015ddc70c47a99fa8f2b682cbddde4a2bf8544e346447eb013adbcdc 253:1    0   50G  0 dm
  ├─docker-0:36-3241-3c373a7b8bc9c4a2d22e4c6d82ff112d22679dc226834175f4b7a0fc71eec85b 253:2    0   50G  0 dm
  ├─docker-0:36-3241-5ac5006fbca47bcedcfe9c3140cfbfa96b739d1e1a943287607915cd20b8011c 253:3    0   50G  0 dm
  ├─docker-0:36-3241-eaa5b76f2e987165319fb006d1850f7283d9071f01175f17da3d05126fbb7423 253:4    0   50G  0 dm
  ├─docker-0:36-3241-6bf3bda9ecc67ad639fb127bcdd91610b2dfb3b7b8c8479494bad342fb34c801 253:5    0   50G  0 dm
  └─docker-0:36-3241-3149fd173c6a79bfcd1dfb0c94d07a77caf3e1bd605106b0f8ad9affcae29ef3 253:6    0   50G  0 dm
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# swapon -v
NAME      TYPE      SIZE USED PRIO
/dev/xvdg partition  20G   0B   -1
[root@ip-172-31-8-223 /]#


[root@ip-172-31-8-223 /]# cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Mon Nov  9 20:20:10 2015
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=379de64d-ea11-4f5b-ae6a-0aa50ff7b24d /                       xfs     defaults        0 0
/dev/xvdf                                 /opt/IBMDocker                  btrfs   defaults        0 0
/dev/xvdg       swap    swap defaults   0       0
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# swapon -v
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Mon Nov  9 20:20:10 2015
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=379de64d-ea11-4f5b-ae6a-0aa50ff7b24d /                       xfs     defaults        0 0
/dev/xvdf                                 /opt/IBMDocker                  btrfs   defaults        0 0
/dev/xvdg       swap    swap defaults   0       0
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# swapoff -a
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# swapon -a
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]#
[root@ip-172-31-8-223 /]# swapon -v
NAME      TYPE      SIZE USED PRIO
/dev/xvdg partition  20G   0B   -1