Githubs authenticity cannot be established. You may see the error message `The authenticity of host 'github.com (x.x.x.x)' can't be established.`. This will likely happen during composer install on your instance.
We are working on a permanent that will remove any need for custom scripts, whilst maintaining maximum security. (We don't want to blindly accept a key and assume it is Github)
Work around
The current work around, is to ask Github for their keys via https, then add these to the instances known hosts.
Within your PHP-FPM configure script (see "Custom Configuration" in the PHP-FPM Guide) add the folloing line.
if [ ! -d /home/magento/.ssh ]; then
mkdir /home/magento/.ssh
fi
echo -e "$(php -r 'ini_set("user_agent", "MDOQ"); $config = json_decode(file_get_contents("https://api.github.com/meta"), true); $output = ""; foreach($config["ssh_keys"] as $sshKey){ $output .= "github.com ".$sshKey.PHP_EOL;}; echo $output.PHP_EOL;')" > /home/magento/.ssh/known_hosts
chown -R magento:magento /home/magento/.ssh