If you have an instance that doesn't have enough disk, despair not! You can add disk!

If the volume you need more space on is an LVM volume:

[root@dev-master2.bb.releng.use1.mozilla.com ~]# df -h
Filesystem                      Size  Used Avail Use% Mounted on
/dev/mapper/cloud_root-lv_root   35G  1.5G   32G   5% /

then you can expand the volume in-place. If not, you'll need to create a new mountpoint.

Either way, start by adding a new volume to the instance:

• In the EC2 Console, go to "Volumes" and create a new general-purpose volume of the desired additional size.
• Find the volume in the list of volumes, and choose Actions -> Attach Volume
• Choose your instance, and accept the default device name
• On the instance, run `lsblk` and you should see your new disk:

[root@dev-master2.bb.releng.use1.mozilla.com ~]# lsblk
NAME                          MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda                          202:0    0  35G  0 disk
├─xvda1                       202:1    0  61M  0 part /boot
└─xvda2                       202:2    0  35G  0 part
  └─cloud_root-lv_root (dm-0) 253:0    0  35G  0 lvm  /
xvdb                          202:16   0   4G  0 disk /mnt
xvdf                          202:80   0  36G  0 disk

The new one is the last one, which isn't otherwise used. Note that you may also see ephemeral disks here -- that's the 4G xvdb in this case, which cloud-init helpfully formatted and mounted at /mnt. You can use that disk, too, but it is ephemeral -- if you stop the system, then data on that disk goes away. If it's part of your LVM logical root volume, the your instance is kaput. No bueno. Still, that disk is fast and if you just need a few gigs for a few minutes, go ahead and use it.

Expand In Place

This is really easy -- add a new physical volume, extend the volume group to include it, and then resize the logical volume to use the new space.

[root@dev-master2.bb.releng.use1.mozilla.com ~]# pvcreate /dev/xvdf
  Physical volume "/dev/xvdf" successfully created
[root@dev-master2.bb.releng.use1.mozilla.com ~]# vgextend cloud_root /dev/xvdf
  Volume group "cloud_root" successfully extended
[root@dev-master2.bb.releng.use1.mozilla.com ~]# lvresize -L+35G -r /dev/mapper/cloud_root-lv_root 
  Extending logical volume lv_root to 69.94 GiB
  Logical volume lv_root successfully resized
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/mapper/cloud_root-lv_root is mounted on /; on-line resizing required
old desc_blocks = 3, new_desc_blocks = 5
Performing an on-line resize of /dev/mapper/cloud_root-lv_root to 18333696 (4k) blocks.

The value passed to `-L` is generally a bit smaller than the size of the volume you created, due to overhead.

Add New Volume

This is pretty easy, too.

[root@dev-master2.bb.releng.use1.mozilla.com ~]# mkfs.ext4 /dev/xvdg
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
655360 inodes, 2621440 blocks
131072 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2684354560
80 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632

Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 24 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
[root@dev-master2.bb.releng.use1.mozilla.com ~]# echo '/dev/xvdg /builds auto defaults,noatime 0 2' >> /etc/fstab 
[root@dev-master2.bb.releng.use1.mozilla.com ~]# mount /builds
[root@dev-master2.bb.releng.use1.mozilla.com ~]# df -h /builds
Filesystem      Size  Used Avail Use% Mounted on
/dev/xvdg       9.8G   23M  9.2G   1% /builds