Unable to run serverspec test on GCP packer instance

I am struggling to run serverspec test on GCP packer instance from local machine. I have created a packer json config file as follows to create an image on GCP:

{
"variables": {
    "project": "gcp-project",
    "image_family": "centos-7",
    "username": "centos",
    "zone": "us-central1-c",
    "version": "latest"
},

"builders": [
    {
        "type": "googlecompute",
        "account_file": "account.json",
        "project_id": "{{user `project`}}",
        "zone": "{{user `zone`}}",
        "source_image":"centos-7-v20171025",
        "image_name": "sftp-{{user `image_family`}}-{{user `version`}}-{{timestamp}}",
        "image_family": "{{user `image_family`}}",
        "image_description": "sftp - from packer",
        "ssh_username": "{{user `username`}}",
        "machine_type": "g1-small"
    }
],

"provisioners": [
    {
        "type": "shell-local",
        "command": "rake spec TARGET_HOST=remotehost"
    }
]

}

and i am executing rake spec TARGET_HOST=(ip of packer instance) to run serverspec test from local machine and spec_helper.rb is configured with ssh login as follows:

host = ENV['TARGET_HOST']
options = Net::SSH::Config.for(host)
options[:user] = 'centos'
set :host,        options[:host_name] || host
set :ssh_options, options

and Rakefile is configured to run test from specific folder.

after running packer build command packer build -var-file=variables.json sftp.json| tee build.log

it fails with

Net::SSH::AuthenticationFailed:
Authentication failed for user centos@1.2.3.4

Packer build log

==> googlecompute: Checking image does not exist...
==> googlecompute: Creating temporary SSH key for instance...
==> googlecompute: Using image: centos-7-v20171025
==> googlecompute: Creating instance...
    googlecompute: Loading zone: us-central1-c
    googlecompute: Loading machine type: g1-small
    googlecompute: Loading network: default
    googlecompute: Requesting instance creation...
    googlecompute: Waiting for creation operation to complete...
    googlecompute: Instance has been created!
==> googlecompute: Waiting for the instance to become running...
    googlecompute: IP: 1.2.3.4
==> googlecompute: Waiting for SSH to become available...
==> googlecompute: Connected to SSH!
==> googlecompute: Executing local command: rake spec TARGET_HOST=1.2.3.4
    googlecompute: An error occurred while loading ./spec/1.2.3.4/sftp_spec.rb.
    googlecompute: On host '1.2.3.4'
    googlecompute: Failure/Error:
    googlecompute:   describe service('sshd'), :if => os[:family] == 'redhat' do
    googlecompute:     it { should be_enabled }
    googlecompute:     it { should be_running }
    googlecompute:   end
    googlecompute: Net::SSH::AuthenticationFailed:
    googlecompute:   Authentication failed for user centos@1.2.3.4

Due to this error I am unable to run serverspec test from local machine using ssh on remote packer instance.

any answer will be appreciated. thanks very much.

It seems like you are missing the password for centos user.

Add this to spec_helper.rb:

options[:password] = ENV['LOGIN_PASSWORD']

And ajust your shell-local to:

{
    "type": "shell-local",
    "command": "LOGIN_PASSWORD='{{ user `sftp_password` }}' rake spec TARGET_HOST=remotehost"
}