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


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