This is an example of a daemon process that monitors a filesystem mountpoint and automatically expands it when free space falls below a configured threshold. New Amazon EBS volumes are added to the instance as necessary and the underlying filesystem (BTRFS or LVM with ext4) expands as new devices are added.

1. Code is running on an AWS EC2 instance
2. The instance and AMI use HVM virtualization
3. The instance AMI allows device names like /dev/xvdb* and will not remap them
4. The instance is using a Linux based OS with either upstart or systemd system initialization
5. The instance has a IAM Instance Profile with appropriate permissions to create and attach new EBS volumes. See the IAM Instance Profile section below for more details
6. That prerequisites are installed on the instance:
   1. jq
   2. btrfs-progs
   3. lvm2
   4. unzip

Provided in this repo are:

1. A script that creates and attaches new EBS volumes to the current instance
2. A daemon script that monitors disk space and expands the targeted filesystem using the above script to add EBS volumes as needed
3. Service definitions for upstart and systemd
4. Configuration files for the service and logrotate
5. An installation script to configure and install all of the above
6. An Uninstallation script to remove the service daemon, unmount the filesystem, and detach and delete any ebs volumes created by the daemon
7. An example cloud-init script that can be used as EC2 instance user-data for automated installation

The easiest way to set up an instance is to provide a launch call with the userdata cloud-init script. Here is an example of launching the Amazon ECS-Optimized AMI in us-east-1 using this file:

aws ec2 run-instances --image-id ami-5253c32d \
  --key-name MyKeyPair \
  --user-data file://./templates/cloud-init-userdata.yaml \
  --count 1 \
  --security-group-ids sg-123abc123 \
  --instance-type t2.micro \
  --iam-instance-profile Name=MyInstanceProfileWithProperPermissions

that installs required packages and runs the initialization script. By default this creates a mount point of /scratch on a encrypted 100GB EBS volume. To change the mount point, edit the cloud-init script file and supply additional options to the install script to suit your specific needs. Install options are shown below.

Install Amazon EBS Autoscale

    install.sh [options] [[-m] <mount-point>]

Options

    -d, --initial-device DEVICE
                        Initial device to use for mountpoint - e.g. /dev/xvdba.
                        (Default: none - automatically create and attaches a volume)
                        If provided --initial-size is ignored.

    -f, --file-system   btrfs | lvm.ext4
                        Filesystem to use (default: btrfs).
                        Options are btrfs or lvm.ext4

    -h, --help
                        Print help and exit.

    -m, --mountpoint    MOUNTPOINT
                        Mount point for autoscale volume (default: /scratch)

    -s, --initial-size  SIZE
                        Initial size of the volume in GB. (Default: 200)
                        Only used if --initial-device is NOT specified.
    
    -t, --volume-type   VOLUMETYPE
                        EBS volume type to use. (Default: gp3)

In the above, we assume that the MyInstanceProfileWithProperPermissions EC2 Instance Profile exists and has the following permissions:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ec2:AttachVolume",
                "ec2:DescribeVolumeStatus",
                "ec2:DescribeVolumes",
                "ec2:DescribeTags",
                "ec2:ModifyInstanceAttribute",
                "ec2:DescribeVolumeAttribute",
                "ec2:CreateVolume",
                "ec2:DeleteVolume",
                "ec2:CreateTags"
            ],
            "Resource": "*"
        }
    ]
}

Please note that if you enable EBS encryption and use a Customer Managed Key with AWS Key Management Service, then you should also ensure that you provide appropriate IAM permissions to use that key.

This sample code is made available under the MIT license.