Simple Distributed Blackboard

• A program that runs on several machines

• Clients post to any server using a web browser

• Store all received data

• Propagate the newly received data

  • to all the other boards

  • in a peer-to-peer manner

Communications between a client and any server

• HTTP requests

  • GET / -> display the page

  • GET /board -> display the content of the board (the data)

  • POST /board -> add a new value to the board

• HTTP Status

• We can inform the client upon a request

  • 200: OK

  • 400: Bad Request (But this should never happen!)

Some hints

• Keep a list of all vessels in each vessel

• Upon a post

  • Send the update to all other vessels

  • But don’t wait for the other to reply before responding to the client!

  • Store the value, it should be shown at the next refresh

• HTTP formatting

  • Do not care how it looks as long it is usable

• The mininet script lab1.py calls a python script called server/server.py

  • The script also provides the server IP as input to the script

Task 1: Make it work https://youtu.be/R_g3SpWsUV8

• Demonstrate that the distributed blackboard works

• Use at least 8 vessels/blackboards

• Do 3 posts and show them on the other blackboards

Task 2: Modify and Delete values https://youtu.be/ugkoNUJ0PDQ

• A user must be able to delete or modify a post

• Once a post is either modified or deleted, a vessel should propagate this change to other vessels

Task 3: Is the system consistent? https://youtu.be/_OZzknPRXKo

• Can it happen that two vessels show different blackboards? Why?

• Even when all data was reliably send to all vessels, and then we hit refresh afterwards