Allow AMI block device mapping to be created without snapshot

[otterley]

I have a use case where I have two launch_block_device_mappings, /dev/sda1 (root device) and /dev/sdb (data device). The data device exists during the build phase to satisfy some build-time prerequisites, but the actual volume content can be discarded at the the end of the build. The device can also be quite small.

Meanwhile, there are two ami_block_device_mappings of the same device names, /dev/sda1 and /dev/sdb. I'd like /dev/sdb NOT to be associated with a snapshot, since at launch time the instance should have a fresh volume. But Packer seems to always associate it with a snapshot because the device was mapped at launch time. Setting snapshot_id to "" seems to have no effect.

[SwampDragons]

Maybe I'm misunderstanding your use case -- does delete_on_termination not work for you?

[otterley]

No, it doesn't. It sets the flag on the attachment, but doesn't change the snapshot ID associated with it.

As a hack, I tried to create a temporary attachment to /dev/sdf in launch_block_device_mappings and then add /dev/sdb to ami_block_device_mappings. So my mappings looked like this:

    "launch_block_device_mappings": [{
      "device_name": "/dev/sda1",
      "delete_on_termination": true,
      "encrypted": false,
      "volume_size": "100",
      "volume_type": "gp2"
    },
    {
      "device_name": "/dev/sdf",
      "delete_on_termination": true,
      "encrypted": false,
      "volume_size": "100",
      "volume_type": "gp2"
    }],
    "ami_block_device_mappings": [{
      "device_name": "/dev/sda1",
      "delete_on_termination": true,
      "encrypted": false,
      "volume_size": "100",
      "volume_type": "gp2"
    },
    {
      "device_name": "/dev/sdb",
      "delete_on_termination": false,
      "encrypted": true,
      "volume_size": "1000",
      "volume_type": "gp2"
    }]
  }]

This created the /dev/sdb mapping without a snapshot, but /dev/sdf remained associated with the AMI as a block device mapping, even though I didn't specify it (and don't want it).

[tomelliff]

This confused me as well because the docs state (emphasis mine):

launch_block_device_mappings (array of block device mappings) - Add one or more block devices before the Packer build starts. These are not necessarily preserved when booting from the AMI built with Packer. See ami_block_device_mappings, above, for details.

I'm not sure I understand what that emphasised comment means if the launch volumes are associated with the snapshot?

In my case I want to create an AMI that has some application data stored on a separate EBS volume and is bootstrapped when the application is installed. I want to discard this application data and then I will use Terraform to attach the persistent volume to a new instance in its place. Either a user data script or a Terraform remote provisioner would then execute a mount -a to mount the persistent volume.

[riponbanik]

I have got a wired issue recently, a ghost ephemeral device is getting attached, even though it was not created with launch_block_device_mappings and launch_block_device_mappings when launching via terraform.

"ebs_block_device.4241468425.device_name": "xvdco",
"ebs_block_device.4241468425.encrypted": "true",
"ebs_block_device.4241468425.iops": "300",
"ebs_block_device.4241468425.snapshot_id": "",
"ebs_block_device.4241468425.volume_size": "100",
"ebs_block_device.4241468

My block device mapping is below -

"launch_block_device_mappings": [
{
"device_name": "/dev/sda1",
"volume_type": "gp2",
"volume_size": 100,
"delete_on_termination": true
},
{
"device_name": "/dev/sde",
"delete_on_termination": true,
"volume_size": "80",
"volume_type": "gp2"
},
{
"device_name": "/dev/sdf",
"delete_on_termination": true,
"volume_size": "100",
"volume_type": "gp2"
},
{
"device_name": "/dev/sdg",
"delete_on_termination": true,
"volume_size": "100",
"volume_type": "gp2"
},
{
"device_name": "/dev/sdi",
"delete_on_termination": true,
"volume_size": "100",
"volume_type": "gp2"
}
],
"ami_block_device_mappings": [
{
"device_name": "/dev/sda1",
"volume_type": "gp2",
"volume_size": 100,
"delete_on_termination": true
},
{
"device_name": "/dev/sde",
"delete_on_termination": true,
"volume_size": "80",
"volume_type": "gp2"
},
{
"device_name": "/dev/sdf",
"delete_on_termination": true,
"volume_size": "100",
"volume_type": "gp2"
},
{
"device_name": "/dev/sdg",
"delete_on_termination": true,
"volume_size": "100",
"volume_type": "gp2"
},
{
"device_name": "/dev/sdi",
"delete_on_termination": true,
"volume_size": "100",
"volume_type": "gp2"
}
]

[jbouse]

What is the status of this? I'm trying to build a custom AMI built off a source AMI that has a 2nd EBS volume that does not use/require a snapshot but when Packer builds my custom AMI following the template the 2nd EBS volume now has a snapshot that I can't seem to get rid of.

[rickard-von-essen]

Try with https://packer.io/docs/builders/amazon-ebs.html#no_device

[ghost]

This issue has been automatically migrated to hashicorp/packer-plugin-amazon#19 because it looks like an issue with that plugin. If you believe this is not an issue with the plugin, please reply to hashicorp/packer-plugin-amazon#19.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

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