Could not retrieve mirrorlist http://repo.us-west-2.amazonaws.com/latest/main/mirror.list error was
amazon-ebs: 12: Timeout on http://repo.us-west-2.amazonaws.com/latest/main/mirror.list: (28, 'Connection timed out after 10001 milliseconds')
Ensure you are launching to a Public subnet and you are getting a public ip via Subnet defaul behavior or explicit instruction in packer template.