add the following option to your run-instances command:
--block-device-mappings file://mapping.json
Specify the following in mapping.json:
[
{
"DeviceName": "/dev/sda1",
"Ebs": {
"DeleteOnTermination": false,
"SnapshotId": "snap-1234567890abcdef0",
"VolumeType": "gp2"
}
}
]