Notes on host_registry


This document aims at exploring possibilities to setup a website.

Typical topology

Let’s say, I want to create 5 websites with the following names:


I have to buy the two domain-names, and I also have to buy a server (i.e. a computer working 24 hours a day and connected to internet), such as vps, where my web-applications and databases will run.

For each domain-name I can register (almost) any sub-domains. For each sub-domain I can register a A-record (IPv4), a AAAA-record (IPv6) or a CNAME-record (i.e. an alias to an other hostanme) . The wilcard * let you provide an IP-address to all sub-domains, not explicitly registered.


With this typical topology, when someone wants to visit one of the websites from his client-laptop, the following sequence happens:

  1. the laptop asks a DNS server the translation of the hostname of the URL
  2. the DNS returns the corresponding IP-address
  3. the laptop send the http-request to my server
  4. the rever-proxy listening to the standard port-numbers forwards the requests
  5. the web-application process the request and provides the result to the reverse-proxy
  6. the reverse-proxy forward the result to the laptop

By the second http-request, the two first steps are skipped, as the laptop knows already the IP-address of my server.

The reverse-proxy manages to forward the requests to the right application thanks to the destination-hostname written in the http-header. So the reverse-proxy won’t work if you replace the server-hostname with its IP-address in the URL.

Pros and Cons


  • the standard port-numbers are used in the http-request, so the port-number is not shown in the URL
  • the reverse-proxy can also act as load-balancer


  • Websocket runs over the intermediate reverse-proxy
  • restriction by ssl / https certificates
  • the reverse-proxy process might become a bottle-neck
  • the equivalence ip-address:port <> hostname:port is broken

The new fact

nodejs offers the capacity of directly serving http-requests from internet. Before nodejs, when generating the html-pages with perl, php or python, a revers-proxy, such as apache or nginx, was required.

Notice, that nowadays, some reverse-proxy are implemented with nodejs with some of the following solutions:

So now, each web-application, implemented with nodejs, can directly face internet. The wish to get rid of the reverse-proxy is getting higher. Two options are described below:

  • a port-redirection service
  • a service-registry


This solution is implemented in this git-repository.

_images/topology_with_port_redirection.png _images/sequence_with_port_redirection.png

By the second http-request, the four first steps are skipped, as the laptop knows already the IP-address and the port-number of the web-application.

Pros and Cons


  • each web-application works nicely independently. No central process.
  • Websocket and https certificates are served directly
  • the equivalence ip-address:port <> hostname:port works as expected


  • the port-number of the web-application if visible in the URL of the http-request

Service registry

The idea is more futuristic and not implemented yet.

_images/topology_with_service_registry.png _images/sequence_with_service_registry.png

Some more ideas for the service registry:

  • hash instead of a service-name
  • the service could update its IP-address and port-number dynamically
  • the load-balancing could be implemented from the client-side (with a list of servers for each service)