Install Docker if you haven't already. You want the fancy UI version. You can get it via homebrew/cask
brew cask install docker
Now launch the application and wait for it to download/update/run itself.
open /Applications/Docker.app
Pull open the Docker menu from your toolbar and click 'Preferences' then 'Advanced'
Change the Memory from 2.0GB to 4.0GB then click "Apply & Restart"
You'll see a green "Docker Desktop is running" from the dropdown when its ready.
Now set up DDev using Homebrew once again
brew tap drud/ddev && brew install ddev
Visit wherever you wish to keep your sites and set up a working directory.
cd ~/Sites && mkdir df-ddev && cd df-ddev
Stop Apache if you're on OSX.
sudo apachectl stop
Now composer install DF using DDev, initially setting the project config to generic php
ddev config --project-type php
ddev composer create acquia/df-project:dev-8.x-4.x --stability dev --no-interaction --prefer-dist
Once that finishes, you can finish setting up Drupal.
ddev config --project-type drupal8
Now you're playing with power!
ddev start
SUPER POWER.
drush si dfs_one
Updated even easier way to do this while working directly on
acquia/df
brew tap drud/ddev && brew install ddev
git clone git@github.com:acquia/df.git
cd df
composer install
ddev config --project-type drupal8
ddev start
drush si dfs_one