terraform/website/source/docs/providers/aws
Paul Hinze 73d20b4c58 providers/aws: add root_block_device to aws_instance
AWS provides a single `BlockDeviceMapping` to manage three different
kinds of block devices:

 (a) The root volume
 (b) Ephemeral storage
 (c) Additional EBS volumes

Each of these types has slightly different semantics [1].

(a) The root volume is defined by the AMI; it can only be customized
with `volume_size`, `volume_type`, and `delete_on_termination`.

(b) Ephemeral storage is made available based on instance type [2]. It's
attached automatically if _no_ block device mappings are specified, and
must otherwise be defined with block device mapping entries that contain
only DeviceName set to a device like "/dev/sdX" and VirtualName set to
"ephemeralN".

(c) Additional EBS volumes are controlled by mappings that omit
`virtual_name` and can specify `volume_size`, `volume_type`,
`delete_on_termination`, `snapshot_id`, and `encryption`.

After deciding to ignore root block devices to fix #859, we had users
with configurations that were attempting to manage the root block device chime
in on #913.

Terraform does not have the primitives to be able to properly handle a
single collection of resources that is partially managed and partially
computed, so our strategy here is to break out logical sub-resources for
Terraform and hide the BlockDeviceMapping inside the provider
implementation.

Now (a) is supported by the `root_block_device` sub-resource, and (b)
and (c) are still both merged together under `block_device`, though I
have yet to see ephemeral block devices working properly.

Looking into possibly separating out `ephemeral_block_device` and
`ebs_block_device` sub-resources as well, which seem like the logical
next step. We'll wait until the next big release for this, though, since
it will break backcompat.

[1] http://bit.ly/ec2bdmap
[2] http://bit.ly/instancestorebytype

Fixes #913
Refs #858
2015-02-18 13:15:11 -06:00
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r providers/aws: add root_block_device to aws_instance 2015-02-18 13:15:11 -06:00
index.html.markdown Remove extra newline 2015-01-22 16:09:26 -05:00