Back-of-the-envelope Calc

Question 1

Why do we use back if the envelope calculations?

Answer 1

Allows us to ignore nitty gritty details of system design to focus on important aspects. A distributed system has compute notes connected via network, and there is a wide variability of available compute nodes and they can be connected in many different ways.

Question 2

Examples of BOTE calculations:

Answer 2

1. Nb of TCP connections a server can support
2. Nb if requests per second (RPS) a web, database or cache server can support
3. Storage requirements of a service

Question 3

What happens if we choose an unreasonable BOTE calculation?

Answer 3

Flawed design

Question 4

What are the relevant concepts for BOTE calculations?

Answer 4

1. Types of data center servers
2. Realistic access latencies of different components
3. Estimation of RPS that a server can handle
4. Examples of bandwidth, servers and storage estimations

Question 5

What are the commonly used data center server types?

Answer 5

1. Web server
2. Application server
3. Storage server

Question 6

What are characteristics of a web server?

Answer 6

Low RAM, high processor and low HD

Question 7

What are characteristics of application server?

Answer 7

1. High RAM, medium processor and medium HD

Question 8

What are the characteristics of storage server?

Answer 8

Low RAM, medium processor, high HD

Question 9

What are web servers?

Answer 9

First point of contact after load balancers, and are decoupled from application servers. Usually handle API calls from clients.

2011 example: Facebook has