(feat): Resize Logical Volumes

[lasith-kg]

This PR is to add the ability to detect whether a Logical Volume needs to be resized. Rather than following the threshold approach from Physical Volumes, we implement a tolerance approach.

When ebs-bootstrap creates a Logical Volume, it specifies how much percent of the Volume Group it should use. This value is retrieved from lvmConsumption.

cat /etc/ebs-bootstrap/config.yml
devices:
  /dev/sdb:
    fs: ext4
    lvm: ifmx-var
    resizeFs: true
    lvmConsumption: 45

# ebs-bootstrap issues the following command
# lvcreate -l 45%VG -n ifmx-var ifmx-var

When we check how much percent of the Volume Group that the Logical Volume has consumed, we see that it is not exactly the value that we specified.

$ sudo lvs --units b -o lv_name,vg_name,lv_size,vg_size --nosuffix
  LV        VG        LSize       VSize      
  ifmx-var  ifmx-var   7243563008 16101933056

# % usage = (7243563008 / 16101933056) * 100 = 44.9857 %

Process

• We generate a window of allowed usage amounts from a tolerance: (45 ± 0.1)%
• We only resize a logical volume if the current usage is less then (45 - 0.1)%
• We produce an error if the current usage of a Logical Volume is greater than (45 + 0.1)%. This would imply that somebody is attempting to shrink a logical volume. This is a disallowed operation