System Design Freedom

Question 1

What are

Load Balancers

Answer 1

Servers that evenly distribute incoming traffic among web servers that are defined in a load-balanced set to optimize system performance, reliability and capacity.

Question 2

Size of

int32

Answer 2

4 bytes

This is the most common int type used across systems.

Question 3

HTTP Status Code

406

Answer 3

Not Acceptable – Request succeeded but couldn’t generate a response that matches the content type in the Accept header.

Question 4

Size of

float64

Answer 4

8 bytes

This is the most common float type used across systems.

Question 5

What is a

Content Delivery Network ( CDN )

Answer 5

A network of geographically dispersed cache servers used to deliver static content.

Question 6

What is

Database Normalization

Answer 6

Process used to organize a database into tables and columns to reduce data redundancy and improve data integrity.

Question 7

How to estimate

Query Per Second

Answer 7

QPS = number of CPU cores / average time for a request in seconds

Question 8

Define

System tests

Answer 8

System testing, also referred to as system-level testing or system integration testing, is the process in which a quality assurance (QA) team evaluates how the various components of an application interact together in the full, integrated system or application.

Question 9

What is

BASE

Answer 9

Basically Available, Soft state, Eventual consistency - an alternative to ACID.

Question 10

What is

RPC

Answer 10

Remote Procedure Call.

Communication method where a program causes a procedure to execute in another address space.

Calling functions directly from another server.

Question 11

HTTP Status Code

1xx

Answer 11

Informational – Communicates transfer protocol-level information.

Question 12

How to estimate

Latency

Given two resource 1 and resource 2.
Answer both ‘Sequentially’ and ‘Parallelly’

Answer 12

• Sequentially: latency = latency_resource_1 + latency_resoure_2
• Parallelly: max(latency_resource_1, latency_resource_2)

Question 13

What is

CAP Theorem

Answer 13

Consistency, Availability, Partition Tolerance - pick two out of three.

Question 14

What is

Synchronous

Answer 14

Synchronous is a blocking architecture, so the execution of each operation depends on completing the one before it. Each task requires an answer before moving on to the next iteration. Synchronous waits for tasks to complete.

Question 15

HTTP Status Code

4xx

Answer 15

Client Error – This category of error status codes points the finger at clients.

Question 16

What is

Eventual Consistency

Answer 16

A consistency model which allows for some lag in data update recognition, stating that if no new updates are made, eventually all accesses will return the last updated value.

Question 17

Define

Acceptance tests

Answer 17

Acceptance testing, sometimes called UAT (User Acceptance Testing), is a testing technique to verify whether the system works as the end user requested or not. Acceptance testing is run after software testing is complete, and the main purpose isn’t to find bugs in the system but to check if the system works as expected. By running acceptance testing before going live, development teams can ensure users can use the software/app smoothly.

Question 18

Size of

UTF-8 in Chinese

Answer 18

3 bytes

Question 19

HTTP Status Code

409

Answer 19

Conflict – Request is well-formed but conflicts with another resource or permission.

Question 20

HTTP Status Code

2xx

Answer 20

Success – Indicates that the client’s request was accepted successfully.

Question 21

What is

Asynchronous

Answer 21

Asynchronous is a non-blocking architecture, so the execution of one task isn’t dependent on another. Tasks can run simultaneously.

Question 22

What is a

Cache

Answer 22

A temporary storage area that stores the result of expensive responses or frequently accessed data in memory.

Stored in volatile memory, not good at persisting data.

Question 23

What is

Rate Limiting

Answer 23

Control of the frequency of actions in a system, often to manage capacity or maintain quality of service.

Question 24

HTTP Status Code

500

Answer 24

System error – Given when no specific error message is available.

Question 25

# Size of boolean

Answer 25

4 bytes

Question 26

# What is ACID

Answer 26

Atomicity, Consistency, Isolation, Durability - properties of reliable transactions.

Question 27

# HTTP Status Code 422

Answer 27

Invalid parameter – Request well-formed but contained semantic errors. Also used to indicate that a runstate change was attempted on a busy resource.

Question 28

# HTTP Status Code 302

Answer 28

URL redirection

Question 29

# HTTP Status Code 429

Answer 29

Too many HTTP requests in a given period of time.

Question 30

# What is Partition Tolerance

Answer 30

## Footnote System continues to function even if communication fails between nodes.

Question 31

# What are some Cache eviction policy

Answer 31

* Least-recently-used * Least-frequently-used * First-in-first-out

Question 32

# HTTP Status Code 5xx

Answer 32

Server Error – The server takes responsibility for these error status codes.

Question 33

# HTTP Status Code 200

Answer 33

Success

Question 34

# What is a Service-Level Agreement (**SLA**)

Answer 34

SLA is an explicit or implicit contract between a service provider and the users. The SLA documents the set of services the service provider will offer to the user and defines the service standards the provider is obligated to fulfill. ## Footnote A contract of how a service will be designed.

Question 35

# What is Availability

Answer 35

System continues to function even with node reaches failure. High availability is the ability of a service to **remain reachable** and **not lose data** even when a **failure** occurs.

Question 36

# Size of UTF-8 character

Answer 36

1 byte

Question 37

# HTTP Status Code 3xx

Answer 37

Redirection – Indicates that the client must take some additional action in order to complete their request.

Question 38

# What is Vertical scaling

Answer 38

**Vertical scaling** is achieved by increasing the number of CPU cores, memory, and disk storage on a single server. However, the server will reach a point of saturation where increasing the number of components does not further increase the throughput.

Question 39

# HTTP Status Code 423

Answer 39

Resource is busy; please wait and try your request again shortly.

Question 40

# HTTP Status Code 401

Answer 40

Unauthorized – Authentication is required and has failed, or authorization hasn’t been provided

Question 41

# What is Horizontal scaling

Answer 41

**Horizontal scaling** is the method of adding multiple machines to scale the pool of resources. The drawback of horizontal scaling is increased complexity.

Question 42

# What is Diagonal scaling

Answer 42

**Diagonal scaling** is a combination of both vertical and horizontal scaling. Diagonal scaling brings the best of both worlds by increasing or upgrading the components on a single server and replicating the server. Diagonal scaling offers relatively better performance and a reasonable price.

Question 43

# Size of UNIX timestamp

Answer 43

4 bytes

Question 44

# Define Unit tests

Answer 44

In computer programming, unit testing is a software testing method by which individual units of source code—sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures—are tested to determine whether they are fit for use. It is a standard step in development and implementation approaches such as Agile.

Question 45

# What is (Data) Consistency

Answer 45

Data is consistent on all corresponding nodes at the same time, regardless of the user or geographic location. ## Footnote All user see the **same data** at the **same time**.

Question 46

# How to measure Availability time

Answer 46

1. A percentage of **uptime** over a given period 2. MTBF ( Mean Time Between Failure ), the average time **between system failures**. 3. MTTR ( Mean Time To Repair), the average time to **restore** a system after a failure.

Question 47

# HTTP Status Code 404

Answer 47

Not found – Resource can’t be found, may be available in the future.

Question 48

# What is Token Bucket Algorithm | for Rate Limiters

Answer 48

Use a bucket with a capacity that stores token. Every request takes a token. If bucket is empty, drops request and return 429. Refills bucket after a certain time period. ## Footnote Parameters: Bucket Size and Refill rate.

Question 49

# What is a Rate Limiter

Answer 49

Control the **rate of traffic** sent by a client or a service. Limits the number of client requests allowed to be sent over a specific period.

Question 50

# What is **The order for System Design**? * Requirements Engineering * Capacity Estimation * Data Modeling * API Design * System Design * Discuss the Designs in Detail

Answer 50

1. Requirements Engineering 2. Capacity Estimation 3. Data Modeling 4. API Design 5. System Design 6. Discuss the Designs in Detail

Question 51

# What is **Availability**? 1. The percentage of time a system is up and running per year 2. The degree of accessability of data for end users 3. The system's ability to keep data in cache and thereby available 4. The ability of a system to be accessed on a certain range of end user devices

Answer 51

The percentage of time a system is up and running per year

Question 52

# Difference between HTTP and gRPC(or RPC) when chosen in a distributed system?

Answer 52

* HTTP is a protocol based on TCP, which requires handshake, where gRPC or RPC calls the components from a known address (service). * The serialization process is more complicated.

Question 53

# What is DAU and MAU

Answer 53

Daily Active User. Monthly Active User.