Dr. Mark Humphrys

School of Computing. Dublin City University.

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  URI schemes

DCU proxy servers


The Web



HTTP client

Web browser

Uses MIME types.
(a) Plug-in - Runs inside browser process.
(b) Helper application - Separate process.





HTTP server

Some issues to keep servers running fast:
  

Caching





For high-demand sites: Multiple copies of entire site - "server farm" - front end routes requests to different CPUs.

Problem: OK to have all (small size) requests come in through one front end and get routed to searching nodes.
Not OK to have all (large size) replies go back through one front end - bottleneck.
Solution: TCP handoff - trick to have the searching node reply directly in a manner that is invisible to client.
The reply load is therefore distributed over all the nodes.




Server logs

HTTP servers can log all accesses. Can have separate log for errors.



Typical web server logs.
(Apart from being colour-coded. Normal logs are not colour-coded.)
From askapache.com.





URI schemes


Some URL formats.


URI schemes listed above:

Others (media): Others (phone): Others:




Keeping state

Relating one client-server stateless request with other client-server requests.

Identify user (pay-to-view, register, personalisation).
Shopping carts.






Performance (client-side)


Caching



DCU proxy servers

In DCU, some machines communicate with the outside world through a proxy server.
Some communicate directly (not through a proxy).


  1. wwwproxy.computing.dcu.ie = 136.206.11.243 (forwards requests through 136.206.11.249)
    • port: 8000

  2. proxy.dcu.ie alternates between different IP addresses (for load balancing)
    • port: 8080 or 3128
    • lookup shows it alternates randomly between:
      1. 136.206.1.17
      2. 136.206.1.20


To set proxy, something like:
  1. Firefox - Tools - Options - Advanced - Network - Settings
  2. IE - Tools - Options - Connections - LAN settings

You may use a proxy auto-config (PAC) file:

  1. https://computing.dcu.ie/proxy.pac
  2. http://proxy.dcu.ie/proxy.pac


Test the IP address other sites see:



ancientbrain.com      w2mind.org      humphrysfamilytree.com

On the Internet since 1987.

Wikipedia: Sometimes I link to Wikipedia. I have written something In defence of Wikipedia. It is often a useful starting point but you cannot trust it. Linking to it is like linking to a Google search. A starting point, not a destination. I automatically highlight in red all links to Wikipedia and Google search and other possibly-unreliable user-generated content.