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Table of Contents

- [Overview:](#overview)
    - [Approaches to system design in an interview:](#approaches-to-system-design-in-an-interview)
    - [List of System Design Topics:](#list-of-system-design-topics)
    - [References:](#references)

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Overview:

Scalability is the property of a system to handle growing amount of traffic. The scaled program with client-server will act as an online service.

I the case the program is scaled offline, it is known as batch processing

When the input is not fixed and comes as a stream, it is known as Stream Processing.

Approaches to system design in an interview:

Step 1: Gather system requirements
1. Gather Functional Requirements
  - Detailed Problem Statement
  - Describe user’s view of the system in plain English
  - Shows that you can communicate and unpack an open-ended problem
  - Ask clarifying questions
  - Main players, their actions, results etc.
2. Design Constraints and Scalability Requirements (Technical requirements)
  - Number of users, transactions per second etc.
  - The interviewer may give them or may ask the candidate
  - Can be collected at a later step as well
  - CP or AP etc
Step 2: Micro services
- Take the functional requirement and write them as user stories
- Group these user stories to similar business objects
- These become microservices (call them after business objects such as picture service, file service etc)
Step 3: Draw Logical Diagram
- Image of hte microservices connected using arrows.
- Shows how data flows through the system
Step 4: Pick one or two micro services and do a deep dive into them
- Talk about application tier, storage tier and cache tier
- Explain how it works for single user single system, single request.
Step 5: Scale the application, storage and cache tier
Step 6: IF time permits, make final proposal
- Go back to the logical diagram and summarize the microservices.

Microservices

independently depoloyable service modeled around a business domain
Each one is a blackbox for other microservices
They communicate using language independent APIS like REST or HTTP
Small and focused on doing one thing
To define microservices,
- cluster the requirements such that each cluster can be handled indpendentlhyby a different eam
- Rule of thumb is if API and data of two functional requirements, do not look the same, then they belown got two different microservices
- This should tell us if it is a depth oriented problem (1 microservice) or breadth oriented problem ( many microservices
- Always the system has profile, analytics and authentication micro services but do not spend time on these Unless the interview is for one of these teams
Architecture:
- Each microservice has upto 3 tiers:
  - Backend tier or business logic (App Server) - Where the code goes
  - Cache tier for faster resposne time (Cache) - subset of database tier
  - Storage tier for data storage and retrieval (Database) - Store in row-major or col major or files (for unstructured data)

Step 1: Wear the product Management Hat:

Treat interviewer as an end-user/customer
Collect Functional Requirements (max 5 to 6 minutes)
- Detailed problem statement
- High level
- Spend a few minutes to show that youc an communicate given an unknown problem
- The idea is to visualize APIs from the requirements
Collect design constraints
- Numbers, how many, how much
- Required for answering scalability
- Often interviewers throw these back to the candidate, so it is beneficial to reseach on them.
- Can be collected at a later step