What is System Design
Systems design is the process of defining the architecture,
product design, modules, interfaces, and data for a system to satisfy specified
requirements. Systems design could be seen as the application of systems theory
to product development
How to Prepare for System Design
While every system design interview is different,
there are some common steps you should cover, even if the conversation might
not be as sequential as your ideal thought process.
The system design interview is an open-ended
conversation, which you’ll be expected to lead. Try using the following steps
to guide your discussion:
Step 1 — Understand the Goals
Clarifying ambiguities early in the interview is
critical. Candidates who spend time clearly defining the end goals of the
system have a better chance of success than those who don’t. For that reason,
make sure you understand the basic requirements and ask clarification
questions. Start with the most basic assumptions:
·
What is the
goal of the system?
·
Who are the
users of the system? What do they need it for? How are they going to use it?
·
What are the
inputs and outputs of the system?
Even if you’re asked about a well-known product,
you should still share your assumptions about it with your interviewer. You may
find that you and your interviewer don’t have the same assumptions about
products like Twitter, Facebook, or Reddit. In addition to helping you focus,
it also demonstrates product sensibility and good teamwork.
Step 2 — Establish the Scope
Now that you understand the system, try to describe
the feature set that you’ll be talking about. Try to define all the features
that you think of by their importance to the user. You don’t have to get it
right on your first attempt, but make sure that you and your interviewer agree.
Ask clarifying questions, such as:
·
Do we want to
discuss the end-to-end experience or just the API?
·
What clients do
we want to support (mobile, web, etc)?
·
Do we require
authentication? Analytics? Integrating with existing systems?
Take a few minutes to discuss this with your
interviewer, and write it down.
Step 3 — Design for the Right Scale
The same feature set requires a very different
approach for different scales. It’s important to determine the scale so that
you know whether your data can fit on one machine or whether you need to scale
the reads. You might ask:
·
What is the
expected read-to-write ratio?
·
How many
concurrent requests should we expect?
·
What’s the
average expected response time?
·
What’s the
limit of the data we allow users to provide?
Different answers require very different designs,
so getting the scale right is key to success.
Step 4 — Start High-Level, then Drill-Down
Start with covering the end-to-end process, based
on the goals you’ve established. This might include detailing different
clients, APIs, backend services, offline processes, network architecture, data
stores, and how they all come together to meet the requirements.
This is also a good point to identify the system’s
entry-points, such as:
·
User interaction
·
External API
calls
·
Offline
processes
This will allow the conversation to drill down into
potential performance bottlenecks, and decisions about the separation of
responsibilities. Whichever approach you choose to start with, remember to
always start simple, and iterate.
Step 5 — Data Structures and Algorithms (DS&A)
Wait, this again? Yes! Turns out, this is actually
important in designing software systems.
URL shortener? Makes me think of a hashing
function. Oh, you need it to scale? Sharding might help. Concurrency?
Redundancy? Generating keys becomes even more complicated. Same goes for
designing an analytics system, a news feed, or a Q&A forum, each with its
own set of common DS&A.
Don’t forget to account for your scaling
requirements, where analyzing runtime and memory complexity really becomes
handy.
Step 6 — Tradeoffs
Almost every decision will involve a trade off.
Being able to describe them in real time, as you’re suggesting solutions, shows
that you understand that complex systems often require compromises and allow
you to demonstrate your knowledge regarding the pros and cons of different
approaches. Since there’s no one correct answer, having this discussion will
give your interviewer the impression that you’re practical and will use the
right tool for the job.
A few common examples might include:
·
What type of
database would you use and why?
·
What caching
solutions are out there? Which would you choose and why?
·
What frameworks
can we use as infrastructure in your ecosystem of choice?
Practice is Key
While you can definitely hone down the theory by
yourself, the last piece of the puzzle is practice. Make sure to apply these
steps time and time again, answering questions about modern system design with
real peers.
It’s the combination of knowledge, technique, and
practice, that’ll enable you to land your dream job.
Additional Resources
Articles/Blogs:
·
Exponent’s
System Design Interview Prep Course — An online course with mock
interview videos and lessons to help you ace the system design interview
·
System Design
Cheat Sheet — A guide on the key topics within system design
·
The
Log: What every software engineer should know about real-time data’s unifying
abstraction — A lengthy article about logs and tradeoffs
·
High Scalability — A blog about how
real-world systems are designed
·
The Architecture of Open Source
Applications (Volume 2): Scalable Web Architecture and Distributed Systems —
An article about some of the key issues to consider when designing large
websites
·
Distributed Systems Reading List —
A list of articles on distributed systems to help change the way you think
Videos:
·
System Design Mock
Interview: Instagram — YouTube walkthrough of a System Design mock
interview about designing Instagram
·
System Design Mock Interview: Facebook
Messenger — YouTube walkthrough of a System Design mock interview
about designing Facebook
·
Intro to Architecture and
Systems Design Interviews — YouTube tutorial made by an ex-Facebook
engineer about system design interviews
·
System Design Introduction
For Interview. — YouTube tutorial made by Tushar Roy about system
design interviews
Top System Design Question
How would you design a tinyURL
system?
A tinyURL is an URL service that allows users to enter a long
URL, and then it returns a shorter, unique URL. A hiring manager might ask this
to allow you the opportunity to show your solid foundation in design. You can
focus on other basics not listed in the example response, like how you create a
unique ID for each URL, how you handle redirects and how you delete expired
URLs.
Example: "When
I was working for a public instant messaging site, I was charged with creating
a simple system where every message was limited to 140 characters. It also
necessitated shortened URLs of about 30 characters. This tinyURL system is also
useful when entering hyperlinks in e-mails or on a smartphone, where there is
room for error. TinyURL is a perfect example of the hashtag table. This data
structure associates keys with values and is a simple connections code. By
using this basic 16-bit hash table, I was able to optimize usability and meet
the needs of the system."
How would you design a search
engine?
Sometimes search engines are
needed within a specific department of a company to systematically locate an
item or important employee information. Hiring managers want to see that you
can tailor designs to the needs of the company. You can detail some of the
overall architecture and explain it, using the foundation below. You can also
consider discussing any other relevant issues such as website front-end
performance, testing search engine improvements and integrating previous search
data and trends in indexing.
Example: "Before
I relocated here, I was working on a project similar to this one. The search
engine I had been enlisted to create needed to work with keyword searches. I
began by building an indexer, which is a piece of software that crawls and
produces results in a data structure. The crawler would put web page links
together and group them or dump them into sets. Then the indexer ran as part of
a reduce job to single things out. For each website, the number of links was
calculated and analyzed for presentation. I had the crawl set for H1 and H2,
rather than H3s. Then I checked outbound links to avoid spammers. Lastly, I
checked the serving results to verify that the design was working at optimal
capacity and relevancy."
How do you design a web crawler, and when
should it be used?
A crawler is a program designed
to visit other sites and read them for information. This information is then
used to create entries for a search engine index. It is typically called a
'bot" or "spider." Be certain to show within your explanation
that you know the intricacies of web crawling.
Example: "Although
crawling the web is a challenging task, I have managed to build one for a
previous project. The crawler scrapes data from a specific sector, in this
case, the fashion industry. I needed to integrate a URL dispatcher, which is a
server whose responsibility is to distribute seed URL to a multitude of
servers. Next, the crawl supervisor passed the URL to bots using the designed
messaging queue. The spider, the basis for any crawler, extracted the data from
the web page and loaded it into my file system. Next, the extract, transform
and load (ETL) cleaned up the content and reformatted it to store it into the
database. In such a way, I was able to crawl the web looking for and organizing
the information needed."
How do you design a shared drive?
Hiring managers ask this to explore algorithm basics and
backgrounds. Before you begin, make sure you understand the purpose of the
task. Knowing if the changes will be registered in real time, if locking will
be necessary and if it needs to be naturally convergent will help you give a
complete answer.
Example: "This
system works on differential synchronization. It is keeping two or more copies
of the same document synchronized with each other in real time, so if a change
is made on one version, the same alteration happens on all the others. It is a
complex challenge, but differential synchronization is scalable and fault
tolerant. The three common approaches are ownership, event passing and three
way merges. I last had to do this to support in-house document sharing for one
of our clients. They wanted real-time collaboration, so three-way merging was
not a good option since changes are lost and cannot take effect, as major
collisions are common. I used event-passing to allow for real-time collaboration
as the locking or ownership approach would only allow the first one opening the
document to make any adjustment. This served our client well, as its employees
were able to work collaboratively even when out of office or on different
schedules."
What is required to design a garbage collection system?
Garbage collection ensures a Java system is running
appropriately and frees a programmer from having to do it manually. Hiring
managers look to see if you know how to truly design the ins and outs of various
systems. A GC makes systems memory efficient.
Example: "One
of my recent clients needed a way to have more memory, but there was an issue
with always having to go in and deal with memory deallocation. The nature
behind garbage collection is to make a system appear as if it has a seemingly
endless amount of memory. What is really happening is that the system is
re-purposing the memory. When a system is running slowly, a garbage collector
goes in and collects what is no longer being used. I set up their system so
that if an object is referenced or recursive in nature, it remains. Next, it
goes through methodically and marks whatever has not been referenced and sweeps
only that. Using the mark and sweep method with the void command helps to
repurpose and open up memory no longer being used. With this in place, my
client had a faster system with less maintenance required."
How do you design a recommendation system?
Recommendation systems help users
find what they want more efficiently. They help clients and customers by
offering alternatives and allowing for choice. Hiring managers inquire about
this to see if you are able to create systems that are user-friendly and
focused.
Example: "One
of my first and most loyal clients had a problem where their customers were
struggling to find options on their website. Their search had to be exact in
order to find the product. I suggested we implement a recommendation system to
help with customer satisfaction and possibly sales. Using the most prominent
approach of collaborative filtering, I designed the system to weave a sort of
information tapestry to give our client's customers suggestions based on user
similarity. The system became more user-friendly and produced a 10% increase in
sales for my client."
Q1) Design TinyURL or bit.ly (a URL shortening service)?
Answer:
Come up with features that the system should support first. Secondly, come up
with the estimated numbers of how scalable the system can be.
While designing a service, there are three things to
consider:
- API(REST
API)-The client’ss communication approach with the service
and a load balancer is the service’s front end.
- Application
Layer – worker threads or hosts that take
the URL and generate the tiny URL for it and store both of them in the
persistence layer.
- Persistence
Layer – Database
Things to analyze:
- Generate
a unique ID for each URL and generate ID’s at scale since 1000’s of URL
shortening requests come every second.
- Service
handle redirects.
- Support
custom URLs.
- Track
click stats
- Delete
expired URLs
2) Design YouTube/Netflix (a
global video streaming service)?
Answer:
Things
to analyze:
- In
videos, the service will be storing and transmitting a huge amount of data
that a large number of users can watch and share them simultaneously.
- Record
statistics about videos, for example, the overall number of views,
up-votes/down-votes, etc.
- Adding
comments on videos in real-time.
Components:
- OC
– Clouds like AWS, OpenConnect which
act as a content delivery network.
- Backend
– Database
- Client
– Any device(Desktop, Android,
iPhone) from which you play the video on YouTube/Netflix.
Let us move to the next System Design Interview
Questions.
3) Designing
Quora/Reddit/HackerNews (a social network + message board service)?
Answer:
Things
to analyze:
The people who use the services can share links or
post questions. Other users can answer questions or comment on the shared
links. So the service should do the following:
- Records
stats for each answer, e.g. the overall number of views,
up-votes/down-votes, etc.
- Users
should be in a position to follow other users or topics
- List
of top questions on the timeline from all the users and the topics they
follow (similar to newsfeed generation).
4) Design Facebook Messenger or
WhatsApp (a global chat service)?
Answer:
This is the basic System Design interview questions asked in an interview.
Things to analyze:
- Design
one on one conversations between users.
- Extending
your design to support group chats.
- What
can be done when the user is not connected to the internet?
- When
to send push notifications?
- How
to provide end to end encryption?
Structure:
Client > Load balancer > Nodes >
Cache(Redis) > Database(Casandra)
5) Design Search
Typeahead(Autocomplete)?
Answer:
Things
to analyze:
- Typeahead
suggestions to be provided.
- Criteria
for choosing the suggestions.
- Does
the system need to be realtime?
- Support
personalization with the suggestions.
- Queries
per second to be handled by the system.
- Amount
of data to be stored.
Part 2 – System Design Interview
Questions (Advanced)
Let us now have a look at the advanced System Design
Interview Questions.
6) Design Dropbox/Google
Drive/Google Photos?
Answer:
Things
to analyze:
- How
to upload/view/search/share files or photos?
- Track
permissions for file sharing.
- Allowing
multiple users to edit the same document.
7) Design Facebook, Twitter or
Instagram?
Answer:
Features
to be considered:
- Some
of the Twitter/Facebook/Instagram features to be supported.
- Need
to support replies to tweets/grouping tweets by conversations.
- Privacy
controls around each tweet.
- Supporting
trending tweets
- Direct
messaging
- Mentions/Tagging
Things to analyze:
- The
number of users and traffic to be handled by the system.
- Amount
of followers the user has.
- The
number of times the tweet has been favourited.
Components required to be designed:
- Newsfeed
generation
- Social
graph
- Systematic
search and storage for posts/tweets.
Let us move to the next System Design Interview
Questions.
8) Design a Web Crawler?
Answer:
Scalable service is required that can crawl the entire web and can collect
hundreds of millions of web documents.
Things to analyze:
- Finding
new web pages.
- Prioritizing
web pages that change dynamically.
- Ensuring
that the crawler is not boundlessly attached to the same domain.
9) Design Uber:
Answer:
This is the frequently asked System Design interview questions in an interview.
Architecture: Monolithic/Micro services(Real-time service,
Front-end(Application) and database)
- The
backend is servicing the mobile phone traffic, and clients connect to the
backend over mobile data.
- Clients
link to the dispatch system, which matches drivers and riders.
- Dispatch
is written almost entirely in node.js.
- Maps/ETA:
In order for dispatch to make an intelligent choice, it is important to
get maps and routing data.
- Services:
Business logic services mostly written in python.
- Databases:
Postgres, Redis, MySQL.
Things to analyze:
- Customer
requesting a ride and how to economically match them with the nearby
drivers.
- Storing
tons of geographical locations for drivers and riders who are always on
the move.
- Handling
updates to driver locations.
10) Design an API Rate Limiter(Github)?
Answer:
Things
to analyze:
- Limiting
the number of requests an entity can send to an API within a time window,
for example, ten requests per second.
- Rate
limiting should work for a scattered setup, as the APIs are reachable
through a group of servers.
1)
What is System Design?
System
design is a process of defining the elements of a system such as the
architecture, components, modules, and various interfaces.
2)
What are the three most essential skills of system designer?
Important
skills for system designer are:
- User interaction
- External API call
- Offline processes
3)
How to design traffic control software?
To
design a system for the traffic control system, as a software engineer, you
need to make sure you know how to transition from one state to another. For
example, Red to Green and from Green to Orange to Red, etc.
4)
What is the benefit of a designing system like Pastebin?
Pastebin
helps you design a system to paste code or text. You can share a link to that
code anywhere you want. It’s not an online code editor, yet you can use this, a
tool to store any text.
5) As
a system designer, how you can design a universal file sharing and storage apps
like Google Drive or Dropbox?
The
above mention apps are used to store and share files, photos, and other media.
We can design things like allowing users to upload/search/view files or photos.
It checks permissions for file sharing and enables multiple users to make
changes in the same document.
6)
How can you design an ATM system?
An
ATM helps a user to deposit and withdraw money. It also allows users to see
their account balance. You need to make a design plan to create this system.
7)
How can you design a web crawler like Google?
A web
crawler visits your website and crawls all your page links and indexes so that
it appears in a Google search result.
A
crawler should be used for searching a specific file in a set of directories.
Designing such a system requires lots of research and time.
8)
What are the things you kept in mind while Designing a web crawler tool?
To
design this, you need to analyze:
- Finding new web pages.
- Prioritizing web page which changes
dynamically
- You also need to ensure that crawler shouldn’t
be boundlessly attached to the same domain.
9)
How can approach to design global cab services like Uber or Ola?
Uber
and Ola are two widely used cab provider. It establishes communication between
drivers and passengers. You need to create a module for GPS, rate calculation,
current location, driver, and client information.
10)
How do you approach to design a message board service sites?
HackerNews,
Reddit, Quora are some of the most popular social network sites where users can
post questions or share links. This type of system allows other users to answer
questions or comment on the shared links.
11)
What is the benefit of designing an application like Airbnb?
It
helps you to upload rooms for rent and other users to rent them. Other vital
features are for
- Publishers
- Admins
- Subscribers
12)
How can you design an API Rate Limiter?
Here
are the points that you need to keep in mind while designing an API Rate
Limiter system:
- Limit the requests which any user can send to
an API within a time window, i.e., 15 requests per second.
- The rate-limiting should work according to
distributed setup because the APIs are accessible only for a cluster of
servers.
- You need to make sure how you would handle
throttling.
13)
How do you approach system design?
Here
are things that you need to keep in mind while designing this system:
- Helps users to search nearby friends or
places.
- Check the ranking of place based on distance
and user reviews.
- Store location data according to the
population of the density of that area.
14)
What are the important structured tools?
Important
structure tools are:
1)
Data Flow Diagrams, 2) Data Dictionary, 3) Decision Trees, 4) Structure
English, and 5) Pseudocode.
15)
In System Design process, what is Requirements Determination?
A
requirement is most important for a new system which includes processing or
capturing of data, controlling the activities of a business, producing
information and supporting the management.
Requirement
determination helps you to study the existing system and to gather details to
find out what are the requirements, how it works, and what kind of improvements
should be made.
16)
How can you design a Twitter Clone?
Twitter
is the most popular messaging service which allows you to broadcast message to
all the people who are following you.
When
you tweet, your follower able to read those messages, they can also retweet or
like. To design such type of apps, you should include standard features like
followers, tweet, hashtag, etc.
17)
How can you design autocomplete functionality?
Here
are important things for developing autocomplete functionality:
- Typeahead suggestion to be provided.
- Queries per second handled by the system.
- Support personalization with the suggestions.
- Amount of data to be stored.
18)
Which is the primary tool used for structured Design?
Structure
charts is a primary tool used for structured Design.
19)
What are the important aspects of the System Study?
System
study is essential to design any system.
Three
most important aspect of System Study are:
- Identifying current issues and establishing
new goals.
- Study of an existing system.
- Documenting the existing system.
20)
What is the Step by step process to solve specific issues called?
This
process is known as an algorithm which plays a significant part for system
designing.
21)
What is the approach used in top-down analysis and Design?
To
approach top-down analysis, you need to identify a top-level function then
create a hierarchy of lower-level module and components.
22)
Explain the term controller
A
controller is a program component which helps you to make decisions and directs
other components.
23)
Which of the following is not a factor in the failure of the system?
The
size of the organization can’t be considered as a factor for system development
and designing projects.
24)
Documentation should be prepared on which state?
Documentation
should be prepared at every stage of system designing.
25)
In the system design process, where is problem analysis done?
Problem
analysis is done at the systems analysis phase.
26)
What do you know about the app booking app like book my show?
Book
my show allows users to book their ticket for shows, events, movie, or
sports. It will enable them to pay and get a refund of movie tickets.
27)
What are the Types of Documentation in System Design?
Four
types of documentation are:
- Program documentation
- System documentation
- Operations documentation
- User documentation
Tips for any SDI Question
Start each problem by stating what you know: List all required features of the system, common problems you expect to encounter with this sort of system, and the traffic you expect the system to handle. The listing process lets the interviewer see your planning skills and correct any possible misunderstandings before you begin the solution.
Narrate any trade-offs: Every system design choice matters. At each decision point, list at least one positive and negative effect of that choice.
Ask your interviewer to clarify: Most system design questions are purposefully vague. Ask clarifying questions to show the interviewer how you’re viewing the question and your knowledge of the system’s needs.
Discuss emerging technologies: Conclude each question with an overview of how and where the system could benefit from machine learning. This will demonstrate that you’re not just prepared for current solutions but future solutions as well.
