EC2 Mac setup for the Elastic CI Stack for AWS

You can run your builds on AWS EC2 Mac using Buildkite's CloudFormation template. This template creates an Auto Scaling group, launch template, and host resource group for maintaining a pool of EC2 Mac instances that run the Buildkite agent. Using Buildkite agents, you can run pipelines and build Xcode-based software projects for macOS, iOS, iPadOS, tvOS, and watchOS.

As you must prepare and supply your own AMI (Amazon Machine Image) for this template, macOS support has not been incorporated into the Elastic CI Stack for AWS.

Using an Auto Scaling group for your instances ensures booting your macOS Buildkite Agents is repeatable, and enables automatic instance replacement when hardware failures occur.

Before you start

You should have familiarity with:

  • AWS VPCs
  • AWS EC2 AMIs
  • macOS GUI

You must also choose an AWS Region with EC2 Mac instances available. See Amazon EC2 Mac instances and Amazon EC2 Dedicated Hosts pricing for details on which regions have EC2 Mac Dedicated Hosts.

Minimum allocation

Dedicated macOS hosts on AWS have a minimum billing period of 24 hours. However you can scale instances running on the host at will.

See also the Amazon EC2 Mac instances user guide for more details on AWS EC2 Mac instances.

Step 1: Choose a VPC layout

Before deploying this template you must choose a VPC subnet design, and which VPC security groups your instances will belong to.

Depending on your threat model, you may find running instances in your default VPC's public subnets with a public IP address suitable. Otherwise, you may wish to explore options like separate public/private subnets with a NAT Gateway, and a bastion instance or a VPN to access the private instances over SSH and VNC. See the AWS VPC Design documentation for more details, and the AWS VPC quick start for a ready-made CloudFormation template.

EC2 Mac Dedicated Hosts are not available in every Availability Zone in the supported regions. You need to provision a VPC subnet in all of your region's Availability Zones to maximize the size of your instance pool.

You also need to configure or define the VPC security groups your instance network interfaces will belong to. At a minimum, inbound SSH access is required to set up your initial template EC2 AMI.

Step 2: Build an AMI

Before deploying this template, you must create a template AMI that will be horizontally scaled across multiple instances.

  1. Reserve an EC2 Mac Dedicated Host.
  2. Boot a macOS instance using your desired AMI on the Dedicated Host. Ensure the root disk is large enough for the version of Xcode you plan to download and install.
  3. Configure the instance VPC subnet, security groups, and key name so that you can access the instance.
  4. Using an SSH or AWS SSM session:
    • Set a password for the ec2-user using sudo passwd ec2-user
    • Enable screen sharing using sudo /System/Library/CoreServices/RemoteManagement/ -activate -configure -access -on -restart -agent -privs -all
    • Grow the AFPS container to use all the available space in your EBS root disk if needed, see the AWS user guide
  5. Using a VNC session (run SSH port forwarding ssh -L 5900:localhost:5900 ec2-user@<ip-address> if direct access is not available):
    1. Sign in as the ec2-user.
    2. Set Automatically log in as to ec2-user in System Preferences > Users & Groups.
    3. Set an empty password in System Preferences > Login Password.
    4. Set Start Screen Saver when inactive to Never in System Preferences > Lock Screen.
  6. Install your required version of Xcode, and ensure you launch Xcode at least once so you are presented with the EULA prompt.
  7. Using the AWS EC2 Console, create an AMI from your instance.

You do not need to install the buildkite-agent in your template AMI, the buildkite-agent will be installed at boot time by the launch template's UserData script.

Step 3: Associate your AMI with a self-managed license in AWS License Manager

To launch an instance using a host resource group, the instance AMI must be associated with a Self-managed license in AWS License Manager.

Using the AWS Console, open the AWS License Manager and navigate to Self-managed licenses. Create a new Self-managed license, enter a descriptive name and select a License type of Cores.

Once your self-managed license has been saved, open the detail view for your license. Open the Associated AMIs tab and choose Associate AMI. From the list of Available AMIs, select your macOS template AMI and then click Associate.

Step 4: Deploy the CloudFormation template

Using the VPC and AMI prepared earlier, prepare values for the following required parameters:

  • ImageId from your AMI set up
  • RootVolumeSize no smaller than the template AMI's root disk
  • Subnets from your VPC set up
  • SecurityGroupIds from your VPC set up
  • IamInstanceProfile if accessing AWS services from your builds, provide an Instance Profile ARN with an appropriate IAM role attached
  • BuildkiteAgentToken an Agent Token for your Buildkite organization
  • BuildkiteAgentQueue the Buildkite Queue your pipeline steps use

There are optional parameters to configure which EC2 Mac instance types to use:

  • HostFamily defaults to mac1
  • InstanceType defaults to mac1.metal

There are also optional parameters to configure the size of the Auto Scaling group:

  • MinSize defaults to 0
  • MaxSize defaults to 3

The default AWS Limit for mac1.metal is three Dedicated Hosts per account region. If you require more than three instances, request an increased limit in the AWS Service Quotas Dashboard.

Deploy using the AWS Console

  • Use the launch button below to create a CloudFormation stack from the latest version of the Buildkite template:

Launch stack button

  • Ensure the selected region in the top menu bar matches the region of your VPC and AMI resources.

  • Give your stack a unique name, and fill in the required parameters.

Deploy using the AWS CLI

To deploy using the AWS CLI, save your parameters in a .parameters.json file and run the following commands:

$ cat .parameters.json
> [
        "ParameterKey": "ImageId",
        "ParameterValue": "ami-0c3a7d0c15048b6b5"
        "ParameterKey": "RootVolumeSize",
        "ParameterValue": "250"
        "ParameterKey": "Subnets",
        "ParameterValue": "subnet-f3e72abb,subnet-f23fe294"
        "ParameterKey": "SecurityGroupIds",
        "ParameterValue": "sg-a09db9d7"
        "ParameterKey": "BuildkiteAgentQueue",
        "ParameterValue": "mac"
        "ParameterKey": "BuildkiteAgentToken",
        "ParameterValue": "[redacted]"

$ make
> sed "s/%v/v0.0.1-9-g1790b0d/" <template.yml >build/template.yml

$ aws cloudformation deploy --stack-name buildkite-mac --region YOUR_REGION --template-file build/template.yml --parameters-override file:///$PWD/.parameters.json

See the AWS CloudFormation Deploy CLI documentation for help using the AWS CLI.

Step 5: Starting your Buildkite agents

Once you have successfully deployed the template, use the deployed stack's Resources tab to find the AutoScaleGroup and open the Physical ID link. Edit the selected Auto Scaling group, and set the Desired capacity to the number of instances you require.

The Auto Scaling group will automatically provision Dedicated Hosts using the host resource group and boot instances on them. The launch template's UserData script will resize the root disk, then install, configure, and start the Buildkite Agent.

EC2 Mac instances are slower to boot and terminate than Linux instances. If want to match your Desired capacity to your workload, consider configuring scheduled scaling for your Auto Scaling group