This regex sets different parts of the url host in variables :

• $domain
• $namespace
• $feature
• $isAPI
• $noMatch

In the host name we want to be able to determine the following:

• Domain: if not on a handled DNS domains, an error 503 'no Service' is returned
• Subdomain: The subdomain contains parts that will redirect the request upstream or send errors, considering the following.
  • empty subdomain redirects to www namespace with code 301
  • Feature: when the first member of the subdomain is prefixed by feature-, redirects to the proper 'feature' upstream built server feature-*.app:8080
  • API: when the subdomain contains api as last element, it is redirected to the API node server (eventually the one of a dedicated feature) [feature-*|default].api:8081
  • Namespace: any single string subdomain different from the 2 above, redirected upstream to the default staging server default.app:8080.
  • noMatch: all uncatched subdomain pattern results in an error 503 no Service

If no upstream server is found, the nginx proxy will return an error 502 maintenance