What syntax do I use for attribute default JSON on chef server?

Hello,

I’m confused as to how to properly create JSON which shall be used on Chef server to override default attributes for cookbooks/recipes.
If I have say cookbook_file resource and need to override say “group” property of it on chef server for environment. How finished JSON shall look like?

cookbook_file '/var/www/customers/public_html/index.php' do
  source 'index.php'
  owner 'web_admin'
  group 'web_admin'
  mode '0755'
  action :create
end