Composer uses a lot of memory when installing Drupal Starter Kits because it has multiple dependencies. To resolve this, you can do one of the following:

• Temporarily increase the memory at the command line. For example,

  php -d memory_limit=2G /usr/local/bin/composer install

• If you have access to the php.ini config file of your servers, you can increase the memory limit to memory_limit=2G or memory_limit=-1. It is a nuclear option that requires root access to the server, and also requires you to restart your webserver for the change to take effect. It is only reasonable for local environments and does not work in ACE/ACSF as you don’t have access. Therefore, Acquia recommends increasing the memory at the command line.