Ephemeral macOS Deployment

Internally, we use this tooling to support the testing of our software on macOS, and the Nix installer itself.

This repository makes many assumptions about your workflow and how you want to use this code. These assumptions are a byproduct of the repository only being used internally, and are likely not difficult to remove. If you use this code and documentation for yourself, consider sending contributions upstream that make it easier for people to use.

Included configuration.nix

Set up macOS machines to automatically erase and provision themselves on a Tailscale network with Buildkite. An erase/reinstall cycle can complete in less than 10 minutes, making it suitable for regular automation.

This README and tooling is public documentation for Determinate Systems, Inc.'s internal use. The goal of making it public is to share the information, and foster the use of ephemeral macOS machines running Nix.

Requirements

• We assume you are using recent Macs with either a T2 chip or Apple Silicon.
• You're using Mosyle MDM. Other MDMs might work, but we're focused on Mosyle. Feel free to send pull requests supporting other MDMs.
• Your Macs are already part of your Apple Business Manager account. Once you have an Apple Business Manager account, they can provide documentation on adding existing Macs.

Hardware Requirements

• A USB-A Logitech Unifying Receiver to act as a mouse and keyboard. The Logitech receiver doesn't need to be configured or paired. Note that macOS is very paricular about the mouse and keyboard hardware directly after erasing. The TinyPilot KVM was not recognized as a mouse. Using a USB hub between the mouse and the computer didn't work either. A cheap Targus mouse's dongle worked as well.
• A USB-C thumb disk formatted and named "CONFIG". SSH keys and other persistent state is stored here.
• A "Dummy" HMDI plug to convince macOS to stay alive. A TinyPilot KVM works as well. Any display should be fine.
• A TRRS 3.5mm male audio jack to disable built-in speakers and microphones. Optional.

Port Availability

2020 M1 Mac Mini

• 2x Thunderbolt 4 / USB-C
• 1x 1Gbase-T Ethernet (10Gbase-T optional)
• 1x HDMI
• 2x USB-A
• 1x 3.5mm headphone jack

2018 Intel Mac Mini

• 4x Thunderbolt 3 / USB-C
• 1x 1Gbase-T Ethernet (10Gbase-T optional)
• 1x HDMI
• 2x USB-A
• 1x 3.5mm headphone jack

2022 M1 (Max, Ultra) Mac Studio

Front:

• 2x Thunderbolt 4 / USB-C
• 1x SDXC

Back:

• 4x Thunderbolt 4 / USB-C
• 1x 10Gbase-T Ethernet
• 1x HDMI
• 2x USB-A
• 1x 3.5mm headphone jack

Erasing a Mac

Select the device in Management, then Devices Overview, then select the More menu. Click Erase device. Change Obliteration Behavior to Do not Obliterate. This requires a T2 or Apple Silicon chip. See "ObliterationBehavior" on https://developer.apple.com/documentation/devicemanagement/erasedevicecommand/command/.

Setting up Mosyle

Automatic Enrollment

After erasing, the machine should fully boot and configure itself without any human interaction. The main tasks here are to configure the region, language, and the initial user account.

Steps

On the Organization tab, select Apple Basic Setup, select Enrollment, click Automated Device Enrollment to get to the Device Enrollment (DEP) page. Click your default profile.

1. Tick If enabled, macOS will automatically advance through all Setup Assistant screens. Available for macOS 11+ when connected to Ethernet.
2. Select your language and region
3. Untick Prompt user to create an account
4. Move on to Create additional local admin during Setup Assistant
5. Enter a full name and use ephemeraladmin for the username. Note that other pieces of this system depends on the user being named ephemeraladmin.
6. Change the Password dropdown to automatically generate a password for each device
7. Tick Set this account to be managed.
8. Set Rename devices after enrollment to mac-ephemeral-%SerialNumber%

Click Save.

Device Groups

The described automation is applied to specific machines through Device Groups.

Steps

On the Management tab, on the left side under Devices, select Device Groups, click Add Device Group.

1. Name it Ephemeral CI
2. Add your macs to the group

Click Save.

Management Profile: Software Update

In general, software updates should be applied quickly and without any user interaction. I want to be able to forget this machine exists after setup, so we have fully automated the update process.

Steps

On the Management tab, on the left side under Management Profiles, select Software Update, click Add new profile.

If the profile type isn't there, click Activate New Profile Type, search for it by name, click Activate, then click Add new profile.

1. Name the profile Automatic Updates
2. All of the defaults are fine as is

Under Profile Assignment, click + Add Assignment, select Devices from specific Devices Group, tick Ephemeral CI.

Click Save.

Management Profile: Energy Saver

If the machine sleeps it is generally not easy to wake it back up. On my Mac Studio, waking it back up requires physically pressing the Power button on the back. I tried using a wireless mouse and a KVM, but neither were able to replace it.

This profile disables sleeping.

Steps

On the Management tab, on the left side under Management Profiles, select Energy Saver, click Add new profile.

If the profile type isn't there, click Activate New Profile Type, search for it by name, click Activate, then click Add new profile.

1. Name the profile Don't sleep
2. Select the Desktop profile tab
3. Set Put the display(s) to sleep after: to 2 minutes
4. Set Put the computer to sleep after: to Never
5. Set Put the hard disk(s) to sleep after to Do not configure this option
6. Under Wake options, tick Wake for Ethernet network administrator access
7. Under Other options, tick Start up automatically after a power failure

Under Profile Assignment, click + Add Assignment, select Devices from specific Devices Group, tick Ephemeral CI.

Click Save.

Management Profile: Security & Privacy: Granting Mosyle access to Removable Volumes

Our provisioning script uses SSH keys stored on an external volume to survive wipes. Apple widely prohibits programs from reading removable storage. This means Mosyle MDM agent cannot access removable media out of the box.

This profile allows Mosyle to access removable storage.

Note that we don't actually enable anything in this profile except a single checkbox for the Self-Service app. That is intentional: that tickbox is all we need.

Steps

On the Management tab, on the left side under Management Profiles, select Security & Privacy, near the top of the screen select the Privacy tab click Add new profile.

If the profile type isn't there, click Activate New Profile Type, search for it by name, click Activate, then click Add new profile.

1. Name the profile Allow Mosyle access to Removable Volumes
2. Tick Install the Privacy Preferences Policy Control settings for the Mosyle Self-Service app to allow access to all necessary files and application data.

Under Profile Assignment, click + Add Assignment, select Devices from specific Devices Group, tick Ephemeral CI.

Click Save.

Management Profile: Custom Commands: Autologin as CI

Autologin is necessary to allow fast erases and reprovisions.

Modern macOS software and hardware has two erase modes: "Erase All Content and Settings" (EACS) and "Obliterate". EACS takes approximately 5 minutes and involves a brief reboot after clearing the existing content and settings. Obliterate completely erases the disk and then rewrites the operating system, annd can take up to several hours. Obliterate is the only option on older hardware.

EACS is the preferred method of implementing an ephemeral macOS machine because of the fast cycle time. In order for EACS to work, the machine must have a "Bootstrap Token" escrowed with our MDM server. The only way to escrow a bootstrap token is to have an administrative user log in.

This profile creates an administrative user with a random, unknown password, and causes it to automatically log in. After creating the user, the machine is rebooted to cause the login to happen.

Steps

On the Management tab, on the left side under Management Profiles, select Custom Commands, click Add new profile.

If the profile type isn't there, click Activate New Profile Type, search for it by name, click Activate, then click Add new profile.

1. Name the profile Autologin as CI
2. Select the Code profile tab
3. Click the code text box
4. Paste the contents of auto-login.sh into the box
5. Click the checkmark in the top right of the Code Edit window
6. Select the Execution Settings profile tab
7. For Execute Command select Only based on schedule or events
8. For Event tick Upon Enrollment Only

Under Profile Assignment, click + Add Assignment, select Devices from specific Devices Group, tick Ephemeral CI.

Click Save.

Management Profile: Custom Commands: Setup SSH

Configure SSH keys and start the SSH daemon for the DEP-managed administrative user, ephemeraladmin.

This script runs very frequently to ensure SSH is both running, and your users' keys are on the machine.

Steps

On the Management tab, on the left side under Management Profiles, select Custom Commands, click Add new profile.

If the profile type isn't there, click Activate New Profile Type, search for it by name, click Activate, then click Add new profile.

1. Name the profile Setup SSH
2. Select the Code profile tab
3. Click the code text box
4. Paste the contents of setup-ssh.sh into the box
5. Edit the list of GitHub user names near line 9 to match your own users
6. Click the checkmark in the top right of the Code Edit window
7. Select the Execution Settings profile tab
8. For Execute Command select Only based on schedule or events
9. For Event untick Upon Enrollment Only
10. For Event tick Every start up of the Mac, Every user sign-in, and Every "Device Info Update".

Under Profile Assignment, click + Add Assignment, select Devices from specific Devices Group, tick Ephemeral CI.

Click Save.

Management Profile: Custom Commands: Install Nix

Installs Nix and nix-darwin, which is configured to run a Buildkite agent and join our Tailscale network.]

Note that right now this code assumes you're installing everything for DetSys purposes. It is an explicit goal for this repository to support configuring things for your purposes without necessarily having to fork the repo. Please open issues discussing or send PRs improving this.

Tailscale Token

First configure a tag to assign to ephemeral macs, by adding this to your Tailscale ACL:

	"tagOwners": {
		"tag:ephemeral-mac-ci": ["you@example.com"],
	}

The actual acquisition of pre-auth tokens is done through Vault on our systems (see setup-vault.sh).

Buildkite Token

Save the buildkite agent token into /Volumes/CONFIG/buildkite.token.

Steps

On the Management tab, on the left side under Management Profiles, select Custom Commands, click Add new profile.

If the profile type isn't there, click Activate New Profile Type, search for it by name, click Activate, then click Add new profile.

1. Name the profile Install Nix
2. Select the Code profile tab
3. Click the code text box
4. Paste the contents of install-nix-fetcher.sh into the box
5. Edit the last lines (repo, branch, cfgpath) to point to your repository and configuration. Note you can use Mosyle's tags and variables to do dynamic configuration dispatch. See the end for an example.
6. Click the checkmark in the top right of the Code Edit window
7. Select the Execution Settings profile tab
8. For Execute Command select Only based on schedule or events
9. For Event untick Upon Enrollment Only
10. For Event tick Every user sign-in

Under Profile Assignment, click + Add Assignment, select Devices from specific Devices Group, tick Ephemeral CI.

Click Save.

Management Profile: Custom Commands: Show Public SSH Key

Shows the public key of the private key generated on the box.

Steps

On the Management tab, on the left side under Management Profiles, select Custom Commands, click Add new profile.

If the profile type isn't there, click Activate New Profile Type, search for it by name, click Activate, then click Add new profile.

1. Name the profile Show Public SSH Key
2. Select the Code profile tab
3. Click the code text box
4. Paste cat /Volumes/CONFIG/buildkite-agent/sshkey.pub into the box
5. Click the checkmark in the top right of the Code Edit window
6. Select the Execution Settings profile tab
7. For Execute Command select Only based on schedule or events
8. For Event untick Upon Enrollment Only
9. For Event tick Every start up of the Mac
10. For Event tick Every user sign-in
11. For Event tick Every "Device info" update"

Under Profile Assignment, click + Add Assignment, select Devices from specific Devices Group, tick Ephemeral CI.

Click Save.

---

Using Mosyle's Variables for Dynamic Dispatch

repo="https://github.com/DeterminateSystems/macos-ephemeral.git"
branch="HEAD"
cfgpath="config.nix"

if (echo "%Tags%" | grep -q "beta"); then
    branch="beta"
    cfgpath="configuration.nix"
fi