16/03/10

Proxying

  A proxy is a program that performs requests on behalf of a client.
  - runs on an intermediary
  - acts as both client and server

  Forward proxies
    - accepts requests from clients (usually browsers but
      perhaps other forward proxies) and may forward
      them to origin servers
    - responses it receives are forwarded to the original
      client
    - close to the client

  Sharing connections
  Caching
  Filtering
  Anonymization
  Transforming responses

  Reverse proxies (surrogates)
    - placed in front of backend servers
    - like a forward proxy, it forwards requests to (one of
      the) backend server(s) and returns results to clients
    - the outside world sees only one IP address/hostname:
      clients think of the reverse prxy as if it were an
      origin server
    - close to the origin server(s)

  Performance
  Security
  Unified front-end

Apache as a proxy

  Suitable only for small- to  medium-scale proxies

  Modules: mod_proxy and mod_proxy_http
	   Caching? mod_cache and mod_disk_cache and/or
                    mod_mem_cache

  Directive for forward proxy

  ProxyRequests On
  
  <Proxy *>
    Order Deny,Allow
    Deny from All
    Allow from .ucc.ie
  </Proxy>
  
  ProxyBlock www.facebook.com porn

  ProxyRemote * http://nextproxy.ie

  Directives for reverse proxy

  ProxyRequests Off

  <Proxy *>
    Order Deny,Allow
    Allow from All
  </Proxy>

  ProxyPass /myscripts/ backend1.example.ie
  ProxyPass /mypages/  backend2.example.ie

  ProxyPassReverse /mypages/ backend2.example.ie