WebFund 2015W Lecture 23

Notes

Two topics for last two lectures:

• What are the fundamentals of web applications?
• Web applications everywhere

Distributed Applications

Applications that run on multiple computers

• separate memory, CPU, storage, communication (I/O)
• can apply this processes, virtual hosts, or physical hosts

Localhost is useful when you want a distributed app on one computer

• GET and POST can go essentially anywhere on the Internet
• allows for flexible combination of code and data

• web applications are the premier form of distributed applications today

• with distributed applications, you don't control all the computers "your" code runs on

Front vs Back end

• separate parts of app for...
  • doing computation/storage/real work (back end)
  • providing the interface (front end)

Can you do "real work" in the front end?

• Yes, but...
• Don't trust the answers

Front end is untrusted, back end is trusted

Modern web apps have many backends and can have multiple front ends (mobile, desktop)

• but "responsive design" says you should have one front end

So why put stuff in the front end?

• lower the load on the back end
• but main reason is latency (of network communication)

Trust

Who do you trust?

• library, runtime authors
• content providers
• ad providers
• whatever else you add to a page

Trust means "who can screw you over"

• if they go bad how badly are you hurt

Amazing the web works at all