high-sierra-base image has only brew pre-installed
high-sierra-xcode-9.4 image is based of high-sierra-base and has only Xcode 9.4 pre-installed

Building Base Image

First, run ./scripts/install-anka-builder.sh to install Anka builder for Packer.

To build the base image (you need to have /Applications/Install macOS High Sierra.app/ installed from App Store):

packer build templates/high-sierra-base.json

We also need to add a port forwarding rule so VMs based of osx-10.13-base image can be SSHable:

anka modify high-sierra-base add port-forwarding --host-port 0 --guest-port 22 --protocol tcp ssh

Building Xcode Images

To build an Xcode image (don't forget to setup FASTLANE_USER and FASTLANE_PASSWORD since they are required by xcode-install):

packer build -var xcode_version="9.4" templates/high-sierra-xcode.json