## COMPONENTS OF WEB APPLICATION ARCHITECTURE
Src : https://www.digitalocean.com/community/tutorials/5-common-server-setups-for-your-web-application
Scalability Lecture at Harvard
Scalability for first 10M users
A service is scalable if it results in increased performance in a manner proportional to resources added. Generally, increasing performance means serving more units of work, but it can also be to handle larger units of work, such as when datasets grow.1
Another way to look at performance vs scalability:
- If you have a performance problem, your system is slow for a single user.
- If you have a scalability problem, your system is fast for a single user but slow under heavy load.
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Four Distributed Systems Architectural Patterns by Tim Berglund
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Twitter's GCP Architecture for Its Petabyte-Scale Data Storage in GCS (Cloud Next '19)
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Scaling Slack - The Good, the Unexpected, and the Road Ahead
Latency is the time to perform some action or to produce some result.
Throughput is the number of such actions or results per unit of time.
Generally, you should aim for maximal throughput with acceptable latency.
How did FB started at first? How much it costed them?
https://techcrunch.com/2012/10/20/facebooks-first-server-cost-85month/
FB: Breaking Ground on Our First Custom Data Center
https://www.facebook.com/notes/262655797130
What are the minimum hardware requirements to run a server at my home? How do you calculate server costs per user for a social networking type platform where storage for each user would max out at 2gb a month/500mb a day? What server size do I need for 30M users? How many active users a day you have? Are the users are normally active during a certain time of the day or will you have peaks in specific dates? How much CPU and RAM each user will be taking? And how much growth your current load has? Whats the bandwith Cost? What are the Activites a normal user will do? Are they watching Videos? Uploading photos/files? Doing computation? Just create txt (blog)? Where are your users located geographically? Where do you log their activity?
courtesy checkcheckzz
Depending on where you are interviewing, go through the company blog. VERY USEFUL IN INTERVIEWS! It really helps if you have an idea of the architecture, as the questions asked will generally be of that domain and your prior knowledge will help out here.
- Airbnb Engineering
- Bandcamp Tech
- BankSimple Simple Blog
- Bitly Engineering Blog
- Cloudera Developer Blog
- Dropbox Tech Blog
- Engineering at Quora
- Etsy Code as Craft
- Facebook Engineering
- Flickr Code
- Foursquare Engineering Blog
- Google Research Blog
- Groupn Engineering Blog
- High Scalability
- Instagram Engineering
- LinkedIn Engineering
- Oyster Tech Blog
- Pinterest Engineering Blog
- Songkick Technology Blog
- SoundCloud Backstage Blog
- Square The Corner
- THE REDDIT BLOG
- The GitHub Blog
- The Netflix Tech Blog
- Twilio Engineering Blog
- Twitter Engineering
- WebEngage Engineering Blog
- Yammer Engineering
- Yelp Engineering Blog
- Smarkets Blog
Your classes should have one single responsibility and no more.
Take validation of an e-mail address as an example. If you place your validation logic directly in the code that creates user accounts, you will not be able to reuse it in a different context. Having validation logic separated into a distinct class would let you reuse it in multiple places and have only a single implementation.
Create code that does not have to be modified when requirements change or when new use cases arise. "Open for extension but closed for modification"
Requires you to break the problem into a set of smaller problems. Each of these tasks can then vary independently without affecting the reusability of remaining components.
MVC frameworks. You have the ability to extend the MVC components by adding new routes, intercepting requests, returning different responses, and overriding default behaviors.
Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it.
No client should be forced to depend on methods it does not use
Dependency injection provides references to objects that the class depends on instead of allowing the class to gather the dependencies itself. In practice, dependency injection can be summarized as not using the "new" keyword in your classes and demanding instances of your dependencies to be provided to your class by its clients.
Dependency injection is an important principle and a subclass of a broader principle called inversion of control. Dependency injection is limited to object creation and assembly of its dependencies. Inversion of control, on the other hand, is a more generic idea and can be applied to different problems on different levels of abstraction.
IOC is heavily used by several frameworks such as Spring, Rails and even Java EE containers. Instead of you being in control of creating instances of your objects and invoking methods, you become the creator of plugins or extensions to the framework. The IOC framework will look at the web request and figure out which classes should be instantiated and which components should be delegated to. This means your classes do not have to know when their instances are created, who is using them, or how their dependencies are put together.
There are a number of reasons developers repeated waste time:
Following an inefficient process
Lack of automation
Reinventing the wheel
Copy/Paste programming
- Deck of Cards: Design the data structures for a generic deck of cards. Explain how you would subclass the data structures to implement blackjack.
- Call Center: Imagine you have a call center with three levels of employees: respondent, manager, and director. An incoming telephone call must be first allocated to a respondent who is free. If the respondent can't handle the call, he or she must escalate the call to a manager. If the manager is not free or not able to handle it, then the call should be escalated to a director. Design the classes and data structures for this problem. Implement a method dispatchCall() which assigns a call to the first available employee.
- Jukebox: Design a musical jukebox using object-oriented principles.
- Parking Lot: Design a parking lot using object-oriented principles.
- Online Book Reader: Design the data structures for an online book reader system.
- Jigsaw: Implement an NxN jigsaw puzzle. Design the data structures and explain an algorithm to solve the puzzle. You can assume that you have a
fitsWithmethod which, when passed two puzzle edges, returns true if the two edges belong together. - Chat Server: Explain how you would design a chat server. In particular, provide details about the various backend components, classes, and methods. What would be the hardest problems to solve?
- Othello: Othello is played as follows: Each Othello piece is white on one side and black on the other. When a piece is surrounded by its opponents on both the left and right sides, or both the top and bottom, it is said to be captured and its color is flipped. On your turn, you must capture at least one of your opponent's pieces. The game ends when either user has no more valid moves. The win is assigned to the person with the most pieces. Implement the object-oriented design for Othello.
- Circular Array: Implement a CircularArray class that supports an array-like data structure which can be efficiently rotated. If possible, the class should use a generic type (also called a template), and should support iteration via the standard for ( Obj o : circularArray ) notation.
- Minesweeper: Design and implement a text-based Minesweeper game. Minesweeper is the classic single-player computer game where an NxN grid has B mines (or bombs) hidden across the grid. The remaining cells are either blank or have a number behind them. The numbers reflect the number of bombs in the surrounding eight cells. The user then uncovers a cell. If it is a bomb, the player loses. If it is a number, the number is exposed. If it is a blank cell, this cell and all adjacent blank cells (up to and including the surrounding numeric cells) are exposed. The player wins when all non-bomb cells are exposed. The player can also flag certain places as potential bombs. This doesn't affect game play, other than to block the user from accidentally clicking a cell that is thought to have a bomb. (Tip for the reader: if you're not familiar with this game, please playa few rounds online first.)
- File System: Explain the data structures and algorithms that you would use to design an in-memory file system. Illustrate with an example in code where possible.
- Hash Table: Design and implement a hash table which uses chaining (linked lists) to handle collisions.
A curated list of System Design interview questions for SDE-1 (Experienced),SDE-2 and above.
Targeted companies: Amazon, Google, Facebook and other biggies.
Design commenting system
Design subscription based sports website which can display scores, game status, history for any games.
Design Netflix => search, video serving, authentication, encryption, dns lookup,caching strategy,serving multi quality video etc
Design a Latency Management System
Design a Library Management System
Design a Notification service
Design ESPN/Cricinfo/Cricbuzz
Design Uber
Design Whatsapp
Design Quora
Design Lookahead system
Design Google Docs/ Collaborative Editing service
Design URL Shortner service
Design RedBus
Design BookMyShow
Design Domain Backdooring system
Design Amazon Locker
Design Movies Review Aggregator System > Data should be fetched from movie rating providers like imdb, rotten tomatoes, etc
Design offline caching system for Ecommerce platform
Design Amazon E-commerce
Design Online chess game/Multiplayer game
Design gaming platform. A number of games can be hosted on this platform. User can login and select a particular game
Design a last-mile delivery platform in case of peak seasons
Design Zomato/Swiggy/Foodpanda
Design Meeting Calendar system
Design Spotify
Design Promo Code API by taking into account Amazon's customer traffic into picture
Design Vending machine with following functionalities ==> Three types of Users : User, Operator, Admin
User can select and buy multiple items at a time. Money can be inputted multiple times (you will get the item if there is a time gap > 30 secs). He can also do window shopping (see only the prices of items and buy nothing)
Operator can load the items and mark the items as expired if needed, gets notified if a product goes out of stock.
Admin can own multiple vending machines, he should have a analytics report of the items purchased in a month. He can also change the prices directly and it should reflect in all the vending machines which he owns.
Exception handling in all the edge cases
Design splitwise
Design Google pay at scale
Design a Job schedular => scalability, fault tolerance, high availability, how scheduler picks up job, how will you take care where one job can run for 30 min and one for 30 hour, how will you distribute jobs on servers. Based on frequency & time how will you execute them ? How will you notify back the user about start/stop or completion of a job ? How will your system know if a job is killed / terminated due to unknown reasons ?
Design Meeting Scheduler
Design Debugger
Design Automatic Parking System
Design a ranking system. We have an infinite supply of words ending with ‘.’ We need to implement a reader program that ranks words on the basis of certain criteria Example: This is my cat. This house belongs to my uncle An amazing country with so many tourist places And so on.. Ranking System criteria : rank the words on the basis of occurrence, for example Output : This:2, is:2, my:2… highest rank (sorted asc or desc based on provided flag) Design it completely and scalable Ranking System
Design Amazon Cart system
Design Google Search
Design Twitter
Design Facebook
Design Snapchat
Design Instagram
Design App-store
Design a music player application
Design a distributed LRU Cache
Design Gmail
Design a recommendation system
Design a food sharing application
Design payment module for Uber app
Design Truecaller type of system
Design performance management system (appraisal workflow system) that can be used across companies.
Design comment system like disqus
Design flight system
Design Tinder
Design survey site like surveymonkey
Design a geographically partitioned multi-player card game, that supports multiple players, multiple games at a time. Each game will have one contractor like ones we have in a bar, He can play a game or just watch it. Integrate payment systems
Design a kind of kindle fire application where we can subscribe news channel and read the news from all publishers as a digital format
Design a realtime Video chat like Google Duo
Design News paper & Magazine subscription system
Design a system like GUVI/Leetcode/Hackerrank/Codechef/Topcoder
Design a concurrent Hashmap
Design an ATM Machine system which can support massive amount of transactions
Design Airport Baggage system
Design Flight Information Display system
Design a conference room booking system for a company which can have offices in multiple cities, each city can have multiple buildings, each building can have multiple floors, each floor can have multiple rooms. Each room can have features like capacitiy, video conferencing available, etc.
Design newsfeed feature of Facebook
Design an efficient Mail delivery system
Design like/dislike feature at Youtube scale.
Design Paypal
Design Air traffic control system
Design a realtime service which tells your friends who is online
Design Google Maps
Design Grammarly