The `SourceDestCheck` attribute can only be changed via
`ModifyInstance`, so the AWS instance resource's `Create` function calls
out to `Update` before it returns to take care of applying
`source_dest_check` properly.
The `Update` function originally guarded against unnecessary API calls
with `GetOk`, which worked fine until #993 when we changed the `GetOk`
semantics to no longer distinguish between "configured and zero-value"
and "not configured".
I attempted in #1003 to fix this by switching to `HasChange` for the
guard, but this does not work in the `Create` case.
I played around with a few different ideas, none of which worked:
(a) Setting `Default: true` on `source_dest_check' has no effect
(b) Setting `Computed: true` on `source_dest_check' and adding a `d.Set`
call in the `Read` function (which will initially set the value to `true`
after instance creation). I really thought I could get this to work,
but it results in the following:
```go
d.Get('source_dest_check') // true
d.HasChange('source_dest_check') // false
d.GetChange('source_dest_check') // old: false, new: false
```
I couldn't figure out a way of coherently dealing with that result, so I
ended up throwing up my hands and giving up on the guard altogether.
We'll call `ModifyInstance` more than we have to, but this at least
yields expected behavior for both Creates and Updates.
Fixes#1020
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/instancestorebytypeFixes#913
Refs #858
An `InstanceDiff` will include `ResourceAttrDiff` entries for the
"length" / `#` field of maps. This makes sense, since for something like
`terraform plan` it's useful to see when counts are changing.
The `DiffFieldReader` was not taking these entries into account when
reading maps out, and was therefore incorrectly returning maps that
included an extra `'#'` field, which was causing all sorts of havoc
for providers (extra tags on AWS instances, broken google compute
instance launch, possibly others).
* fixes#914 - extra tags on AWS instances
* fixes#883 - general core issue sprouted from #757
* removes the hack+TODO from #757
Paul Hinze