2/13 - Web App Architecture

Question 1

What does HTTP (Web Transport Protocol) do?

Answer 1

It specifies requests from clients and responses from a server.

Question 2

What is HTTP built on?

Answer 2

TCP

Question 3

Which port does HTTP use on the server by default?

Answer 3

Port 80

Question 4

What does HTTPS do?

Answer 4

HTTPS ensures authenticity

Question 5

What does HTTPS require?

Answer 5

HTTPS requires a paid certificate

Question 6

Who can initiate communication in HTTP?

Answer 6

Only the client can initiate communication.
• The server can only send data in response
• The client must poll server periodically to support server notification

Question 7

URI Format

Answer 7

Uniform Resource Identifier/Locator

Question 8

What is the PROTOCOL in the following URI?

http://server.com:8888/path/file?p1=v1&p2=v2#x

Answer 8

http

Question 9

What is the HOST in the following URI?

http://server.com:8888/path/file?p1=v1&p2=v2#x

Answer 9

server.com

Question 10

What is the PORT in the following URI?

http://server.com:8888/path/file?p1=v1&p2=v2#x

Answer 10

8888

Question 11

What is the PATH in the following URI?

http://server.com:8888/path/file?p1=v1&p2=v2#x

Answer 11

/path/file

Question 12

What is the QUERY in the following URI?

http://server.com:8888/path/file?p1=v1&p2=v2#x

Answer 12

p1=v1&p2=v2

Question 13

What is the ANCHOR in the following URI?

http://server.com:8888/path/file?p1=v1&p2=v2#x

Answer 13

x

Question 14

Is the anchor in the URI REQUIRED or OPTIONAL?

Answer 14

optional

Question 15

What does GET do?

Answer 15

used to retrieve a resource names by URI

Question 16

What does POST do?

Answer 16

Used for client to send data

Question 17

What is a HTML form for, and what does it do?

Answer 17

• Used as UI element to collect input

* Plays a role in communication (sending parameters)

Question 18

What if we want to keep state?

Answer 18

Server should recognize the client and show the same client ID

Question 19

What happens if you store the client ID in the server?

Answer 19

The problem is that the request and handlers are re-created fresh for each request. It seems that the server does not want to keep state.

The server cannot keep the connection open to all clients who are thinking what to buy next, and it cannot reliably distinguish different clients in different requests (they all appear alike).

We need failure tolerance and to enable load balancing.

Question 20

Failure tolerance

Answer 20

What if the server crashes?

Failure tolerance is is the property that enables a system to continue operating properly in the event of the failure of (or one or more faults within) some of its components. If its operating quality decreases at all, the decrease is proportional to the severity of the failure, as compared to a naively designed system in which even a small failure can cause total breakdown.

Question 21

Load balancing

Answer 21

Allowing other server instances to deal with subsequent requests is required to enable load balancing.

Load balancing aims to optimize resource use, maximize throughput, minimize response time, and avoid overload of any single resource.

Question 22

How do we store client ID in the client?

Answer 22

We do this by using cookies

Question 23

Cookies

Answer 23

• Key value pairs associated with a website stored at the browser for a specified time
• Most cookies are available to Javascript code
• Many security and privacy issues are possible, if used incorrectly