Manage stock Windows AMIs with Ansible (part 1)

Ever wished you could just spin up a stock Windows AMI and manage it with Ansible directly? Linux AMIs usually have SSH enabled and private key support configured at first boot, but most stock Windows images don't have WinRM configured, and the administrator passwords are randomly assigned and only accessible via APIs several minutes post-boot. People go to some pretty awful lengths to get plug-and-play Windows instances working with Ansible under AWS, but the most common solution seems to be building a derivative AMI from an instance with WinRM pre-configured and a hard-coded Administrator password. This isn't too hard to do once, but between Amazon's frequent base AMI updates, and the need to repeat the process in multiple regions, it can quickly turn into an ongoing hassle.

Enter User Data. If you're not familiar with it, you're not alone. It's a somewhat obscure option buried in the Advanced area of the AWS instance launch UI. It can be used for many different purposes; much of the AWS documentation treats it as a mega-tag that can hold up to 16k of arbitrary data, accessible only from inside the instance. Less well-known is that scripts embedded in User Data will be executed by the EC2 Config Windows service near the end of the first boot. This allows a small degree of first-boot customization on a vanilla instance, including setting up WinRM and changing the administrator password; once those two items are completed, the instance is manageable with Ansible immediately!

We'll build up the files throughout the post, but a gist with complete file content is available at https://gist.github.com/nitzmahone/4271319ab8e7acf3330c.

Scripts can be embedded in User Data by wrapping them in <powershell> or <script> tags for Windows batch scripts- in this case, we'll stick to Powershell. The following User Data script will set the local Administrator password to a known value, then download and run a script hosted in Ansible's GitHub repo to auto-configure WinRM:


<powershell>
$admin = [adsi]("WinNT://./administrator, user")
$admin.PSBase.Invoke("SetPassword", "myTempPassword123!")
Invoke-Expression ((New-Object System.Net.Webclient).DownloadString('https://raw.githubusercontent.com/ansible/ansible/devel/examples/scripts/ConfigureRemotingForAnsible.ps1'))
</powershell>

A word of caution: User Data is accessible via http from inside the instance without any authentication. While the following technique will get your instances quickly accessible from Ansible, DO NOT use a sensitive password (eg, your master domain admin password), as it will be visible as long as the User Data exists, and User Data requires an instance stop/start cycle to modify. Anyone/anything inside your instance that can make an http request to an arbitrary host can see the password you set with this technique. A good practice is to have one of your first Ansible tasks against your new instance change the password to a different value. Another thing to keep in mind is that the default Windows password policy is usually enabled, so the passwords you choose need to satisfy its complexity requirements.

Before we get to the Holy Grail of actually using Ansible to spin up Windows instances using this technique, let's just try it manually from the AWS Console first. Click Launch Instance, and select a Windows image, then under Configure Instance Details, expand Advanced Details at the bottom to see the User Data textbox.

Paste the script above into the textbox, then click through to Configure Security Group, and ensure that TCP ports 3389 and 5986 are open for all IPs. Continue to Review and Launch, select your private key (which doesn't make any difference now, since you know the admin password), and wait for the instance to launch. If all's well, after the instance has booted you should be able to reach RDP on port 3389, and WinRM on port 5986 with Ansible (both protocols using the Administrator password set by the script). It can often take several minutes for Windows instances set up this way to begin responding, so be patient!

Let's test this using the win_ping module with a dirt simple inventory. Create a file called hosts with the following contents:

aws-win-host ansible_ssh_host=(your aws host public IP here)

[win]
aws-win-host

[win:vars]
ansible_connection=winrm
ansible_ssh_port=5986
ansible_ssh_user=Administrator
ansible_ssh_pass=myTempPassword123!

then run the win_ping module using Ansible, referencing this inventory file:

ansible win -i hosts -m win_ping

If all's well, you should see the ping response, and your AWS Windows host is fully manageable by Ansible without using a custom AMI!

In part 2, we'll show an end-to-end example of using Ansible to provision Windows AWS instances.