title: SEO Sitemap for Subdomain
body: <p>Basically i have a site call (e.g. domain.com), and i allow my customers to host their site on my domain (e.g. theirsite.domain.com)</p>
  
  <p>I have a sitemap for domain.com, but have no linkage to theirsite.domain.com, as a result, these subdomain(s) cannot be found on google.</p>
  
  <p>I have considered generating the site map dynimcally, but it wouldn't be ideal, as there might have 100,000 sites on my domain, causing huge resource consumption and slow generating time.</p>
  
  <p>Is there any ideal way to let the search engine crawl my domain.com, as well as my customer sites (xx.domain.com)?</p>