`ssh_private_key_file` used for both droplet creation and subsequent connection

[davefp]

Overview of the Issue

Previously I had an issue when providing a private SSH key to connect to my newly created droplet: #19

The fix provided in #20 and shipped with v1.0.1 fixed my issue and I've been using that version ever since.

Now I'm (finally) upgrading to a more recent version and my existing configuration results in a different error.

The private key specified in my config is being used as both the root key when creating the droplet and the ssh key when connecting as a user (which may not be root) to provision the droplet.

In my case, I have a user named deploy that already exists on the base image that I want to connect as. Giving root the same key as deploy is no bueno.

I noticed this because I have that key added to DO already separately, and when trying to create the root key it fails since there's a duplicate.

I believe this bug emerged in the following commit: https://github.com/digitalocean/packer-plugin-digitalocean/commit/0462cbc5d32f1013f2c067116bb836a2ef19030e

Versions of the plugin pre-1.2.0 work as expected.

My desired functionality is to be able to specify the root key and the communicator key separately. If I don't specify a root key then the plugin should generate a temporary one for me, but then connect using the supplied communicator user/key.

Reproduction Steps

1. Create a keypair on the host where you're running packer.
2. Add that key to Digital Ocean.
3. Create a packer buildfile that specifies the private key file but not the key ID from Digital Ocean
4. Run packer build
5. Observe the output (example below)

Plugin and Packer version

Packer: 1.9.4 Plugin: 1.2.0 and up

Simplified Packer Buildfile

variable "deploy_private_key_file" {
  type = string
  default = null
}

variable "digital_ocean_application_image_id" {
  type = string
  default = null
}

build {
  name = "application_server"
  source "source.digitalocean.default" {
    image = var.digital_ocean_application_image_id
    snapshot_name = "backend_server"
    snapshot_regions = ["tor1", "nyc3"]
    ssh_username = "deploy"
    ssh_private_key_file = var.deploy_private_key_file
  }
}

Operating system and Environment details

MacOS 13.6.3

Log Fragments and crash.log files

Full plugin output from my packer run:

Debug mode enabled. Builds will not be parallelized.
application_server.digitalocean.default: output will be in this color.

==> application_server.digitalocean.default: Using existing SSH private key
==> application_server.digitalocean.default: Pausing after run of step 'StepSSHKeyGen'. Press enter to continue. 
==> application_server.digitalocean.default: Pausing after run of step 'nullStep'. Press enter to continue. 
==> application_server.digitalocean.default: Importing SSH public key...
==> application_server.digitalocean.default: Error creating temporary SSH key: POST https://api.digitalocean.com/v2/account/keys: 422 (request "e362b52b-ac39-4c99-b14f-cb6bf0804dc0") SSH Key is already in use on your account
==> application_server.digitalocean.default: Pausing before cleanup of step 'nullStep'. Press enter to continue. 
==> application_server.digitalocean.default: Pausing before cleanup of step 'StepSSHKeyGen'. Press enter to continue. 
Build 'application_server.digitalocean.default' errored after 20 seconds 184 milliseconds: Error creating temporary SSH key: POST https://api.digitalocean.com/v2/account/keys: 422 (request "e362b52b-ac39-4c99-b14f-cb6bf0804dc0") SSH Key is already in use on your account

[davefp]

I've attempted to allow for this by adding a skip_keygen flag that can be set to (you guessed it) skip the SSH keygen step altogether, ~but I'm having trouble getting the new config variable to register correctly.~

~Simply adding it to config.go doesn't seem to be enough. I receive the following error:~

~Error: unsupported attribute "skip_keygen": [{{} skip_keygen}]~

~I'd appreciate guidance on this please.~

I've resolved the previous issue 👍🏻

Here's the WIP PR on my fork: https://github.com/MicroMetrics/packer-plugin-digitalocean/pull/455

Let me know what you think about getting this change into the package proper. Thanks!