System Design Mock Interview: Design Instagram
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- เผยแพร่เมื่อ 13 มิ.ย. 2024
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In this interview, Jacob (Dropbox Software Engineer) answers a system design interview question of designing Instagram, commonly asked in software engineering and technical program management (TPM) interviews.
The diagramming tool we use is called Whimsical: whimsical.com/
Chapters -
00:00:00 Introduction
00:00:09 Question
00:00:35 Answer
00:01:13 Requirements
00:03:41 Scale
00:06:19 Data types
00:14:50 Design
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"And then we can talk about the API a little bit later"
Never talks about API
I know my ass would not get hired if I did that.
Great job.. Thanks for the video.
I think we can add the following:
- Elaborating the DB sharding and partitioning in the system.
- DB Replication, by adding redundant blocks for database based on master/slave relation, where the master is for write, and slaves for read.
- Talking about the data searching, like considering to use Elasticsearch for example.
- Adding a block for CDN to clarify where it should to be in the system diagram.
- Adding a message/uploading queue
- Making an estimation for bandwidth
I think DB Replication is understood for default.
Rest all points are great 👏
This video is great introductory resource, however it is a little bit superficial. Anyway was great watching and looking forward for the other videos on this channel!
Any questions about how to ace a system design interview question like this one? Ask below and we'll answer! Let us know what you liked!
Couldn't we use a NoSQL data schema storing all the photos for a user along with the user object?
The diagramming tool we use is called Whimsical (whimsical.com/) - Don't leave your career to chance. Sign up for Exponent's system design interview course today: bit.ly/3TCpTbn
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Thanks a lot, you clearly explained how to draw the architecture diagram component by component and finally building the whole system. Other popular system design videos missing this.
This is a great example of what you should strive to have completed at the halfway point of the interview.
A good to add would be message queue. As we know, when we update for example a big image, user shouldn't be waiting there for a long time. Also, if we write the huge chunk of data directly to to the image storage, it will explode (storage usually won't have such a big RAM)! Hence, a good practice would be push it to the queue with a publisher, and have multiple listeners to update these images data (binary formats) into the storage.
pushing large objects to S3 won't explode it
@@lagneslagnes and even if it did, where you would store 5mb image? In queue? Azure Blob/S3 are by design much more scalable than any queue that can handle 5mb binaries within a message.
Unreal video! I'm relatively new to Systems Design but this was easy to follow and aligned with a lot of other good information I've been finding on the web. Thank you!
Glad you liked it! Be sure to subscribe for more like this :)
@@tryexponent How can I use this type of whiteboard ? Is it free of I have to pay something to use ?
After scrolling through 100s of SD videos finally I found a way to approach the questions in the interviews. Your step by step approach from start to finish was really helpful. Thanks
Loved the video, great explanation. What is the UI/ tool used here to draw for the system design?
It’s called Whimsical!
I like the pace and structure of this video. What helps is that I worked on my design and looked at this video to see how well I did. One revision I would make is adding a object storage proxy and the backend service would call the proxy instead for protected images. To me, object storage is the toughest part of this problem. Public images can be served with cdn but private photos must retrieve from object storage.
Anyone have any thoughts around the choice to go with SLQ (as opposed to NoSQL)?
I’m relatively new to system design, but Twitter sounds like it would benefit more from the scalability that NoSQL would provide?
Love this! Have my first ever systems design interview tomorrow and the broadness and pace of this interview is perfect!
You got this!
@@tryexponent An update! I'm onto the next round (onsite) in no small part thanks to this video!
@@nickcocks2745 Keep on!
How did it go ? Is that the kind of answer that was expected by your interviewer ?
@@RomainJouin I GOT THE JOB :) so it seems so! It's my first ever software engineering job (YAY!) so they were more looking for how I broke problems down and communicated than they were really grilling me on systems engineering, I managed to also squeeze in a mock interview before the real one and I used this video as reference material
This is a great video and I haven't evenr watched it complete. I really like how the requirements are collected and quantified
Thank you . This video shows that even hard topic like system design can be taught in a simple way . I like this .
Glad it was helpful!
Excellent Video! I was wondering what rationale should an interviewee give if asked about the scalability (specifically, write scalability) after choosing a relational database model?
Wow - You just earned an subscriber - Excellent pace and detail Thanks !!
I loved this video. You explained in such a easy way. i was able to connect everything. Thanks man :)
Really helpful video Jacob, super detailed in explaining the architecture. Thank you
Good explanation. You made a complicated problem easy to follow and understand!
very helpful, can you make a more mock system design interview!!!????? thanks!
Sure thing!
Great video. Have you considered talking more about the APIs?
Thanks for the video! Really enjoyed it as it gives a great exploration of the problem.
However, I think the candidate needs to further explore the scaling of the data and provide estimations about read/write requests per second, traffic and storage needed that we need for instance for 10 years, and what to do when the DB is full that we need to scale vertically (as we you have gone for a MySQL).
Those information will help out understanding the overall scale of our system and brightens the scene for the interviewer that we are set with with expected traffic and can manage to handle the requests.
The feed generation part needs a bit more detail IMO. That's the most challenging part of this. Would you generate it on read or on write? Or a combination of both? Also, what if it's not a linear timeline of events but needs to be ranked? Also, details around comments and replies?
Really wish I had seen this before my second round TPM interview at a major FAANG company. LOL Great video!
Glad you enjoyed it!
Great work , I learnt a lot today and the video was well paced and informative. Thanks
Glad it was helpful!
I think this video is really very generic, so much so that this design could be applied to any problem. Would have loved see you deep diving into details of any one component in this 30 min video. For e.g is database sharing required? Do we need noSQL databases? how would the fan out process work? How to handle influencers who have 5 million followers? Disappointed to see those details missing here.
I would think for say N-Million followers, that work is either broken down aycnch and its broken across a number of shards in a region.
He spent the whole time on the easier part of the design. He didn't model the feed, or describe when and how its built.
@@Damouse007 I think recently I just saw a architecture mock interview for Twitter in which they go over is designing the seed which was actually genuinely helpful it’s a very interesting approach to modeling I would probably look that up if you’re interested
Agreed, this much detail will not clear a system design interview
Thanks so much for this video! I loved it!
We're glad you loved it!
Thank you for posting this! Really helpful!
Its simple and compact, loved it, thanks.
Nice video! Which software do you use for the diagram?
I have a question @22.05, you mentioned that when we will write data, we will write cache as well. If there is consistent write operation happening, you will keep changing cache. Would not it be more inefficient?
Do you have any videos that talk more in depth about mobile architecture? For example battery usage, disk space on the device, networking speeds and data consumption of the device etc.
If not do you know of any resources that have that info? Currently studying for FB design interview as an iOS engineer
I have a system design interview coming up next week, what tool are you using for sketching?
Which tool you used in the interview can you mention please
Great stuff. Please post some mock interviews where the candidates failed. Thank you.
I am not sure that a relational database is the best choice here. There are often relationships in data but sometimes you need to determine the right trade offs in terms of scalability. Though I appreciate that a relational model can be designed to work at such scale (read replicas, sharing etc), I would consider using NoSQL solution for the media metadata api, and a graph database for the activity feed.
Such a great explanation. Thank you.
Can we use graphs to record follow relation between users?
Yes. Graphs. Graphs database is best to store all the user's information & relationships between them. The response time for getting the relationship as well information about the user is so very fast with the Graph database. Graph databases are best suited for this type of many-2-many relationships as compared to the traditional relational databases. I do not agree with this guy saving user's details in the relational database. But basically, you must need all diff kind of databases for diff-diff purpose in such a large scale application. The architecture he designed is a common architecture for a simple mobile app. Have a look how
complex the architecture can be for Instagram/Facebook.
github.com/codekarle/system-design/blob/master/system-design-prep-material/architecture-diagrams/Facebook%20System%20Design.png
Great video, thank you. Good example of CQRS in action. For further improvement it would be a good idea to use another DB for feed generation, because access patterns will be slightly different: OLTP for user actions and OLAP for feed (maybe some recommendation system under the hood).
What program do you to make these designs on your videos?
Great presentation. Thank you :)
Glad it was helpful!
Hello! What are you use for draw structure in this video?
This was an enormous help in my interview today! I adapted the flow to talk about the specific requirements. Calculating scale and talking about the data model with a segue into the overview diagram was very coherent. Most of all it produced every possible opportunity to highlight my experience with the components I presented, which is the overall goal.
I'm so glad this was helpful Alex! Definitely let us know how the interview went!
@@tryexponent I moved forward in the process, and the SDI was a large part of it! I discovered through the interview process about their product and the responsibilities of the role that it was not what I would like to pursue, but that's a different story.
@@thatsamorais584 Congratulations!!
What if you're asked to build a Logging API? Then it would just be client-side right? Would you go into details about servers and databases if it's mostly client-side?
Really nice video! Thanks!
What is this program you're using through the entire video?
Nice pace of the mock interview. However, the diagram can actually fit most of the system. Shouldn't we focus more on how to fan-out photos, generate news feed, etc, which are more specific to "designing Instagram"? I wonder if we only talk about the high-level things and teaching the interviewers those basic architectural concepts (read-write, load balancer, s3, CDN) as this video does can really ace the interview.
I kept waiting for the actual system design to start. Then the video ended. What this video covered is basically the skeleton of any system where you upload/view single files at a time.
Yes found it to be really basic. Even I was looking forward to fanning out photos as well some replication to the dB as only one dB instance is used for both read and write operations for 10 million users
@@BrijeshBolar79 what does fanning out photos mean in this context? and any good resource on db replication / sclaing? thought that part was lacking definitely.
I see that in so many videos on TH-cam. 0 specifics about the actual system, just generic LB, DB schema, object storage stuff. I really wonder if interviews are buying this….
@@tsaregrad they're not. You won't get any reputable offer with details TH-cam videos provide. These are just for the views.
Hi, thank you for proving this video, it is really helpful!
Just to be clear, at 22:41, in the diagram, the cache policy you drawn seems to be a write-around cache policy, but at 21:56, you mentioned write-back cache policy (which I believe write operation is written to Cache first, and then after certain intervals, the data is written to DB). Did I understand this correctly?
Nice video! Do you think you could go over potential bottlenecks and how you would resolve those?
so good, which tool are your using for capturing this all designing detail on one screen
Very good video for very novice engineers looking to learn about systems. However, there are big gaps here when it comes to scaling, ie. using a relational database (which also decreases performance) and having a synchronous system.
I had some questions about this, too. I can see the rationale for an RDBMS but from a scaling perspective, it would surely run into trouble. I was hoping the video might discuss how failover to another Region. The topic of Failover would surely come up in an interview.
Learned a ton from this. Never have had a Systems interview and I am a new grad so my potential onsite coming up has a design portion so trying to grind through these and learn a ton!
Ton?!
doesn't make sense asking a fresh grad system design questions.
I am a new grad as well and have a sys design interview coming up. How deep did you go in the system? what all did you discuss and what all did you leave abstracted?
@@arobot4398 I have a interview coming up that is a system design interview, they are pretty common to be honest
@@arobot4398 most F500s who want to hire anything above entry level often have at least one systems design and architecture interview in the process.
Exponent provides best mock interview videos
Great video! Thanks for creating this content! I thoroughly liked the half hour video. If one thing I could suggest, would be little bit more deep dive into the design - API, sharding, replication etc. Also in case of read, you are connecting the mobile device directly to Object Store, then why not in case of write as well? The device can directly write to object store, and just push meta data through the App server (write). Are there any downsides you were thinking?
I might be wrong, since I'm also not an expert in system design, but my reasoning would be as follows: We can introduce a CDN between S3 and clients, making serving static files much faster. But I'm not sure if we can speed up the upload process (from the client to S3) in a similar way.
Also writing directly to the S3 bucket just doesn't seem right to me from the security perspective
@@stanislausaprankou3495 you can request for a signed url from the server, and use that to upload directly to S3. Passing all those large files through the server is going to add so much unnecessary cost.
What is the tool you are using for drawing/diagraming?
What’s the drawing tool you are using? Looks really nice! Share a link?
Nice. What platform do you use for your presentation (video + slides) - Canva?
Good coverage !!! nice walk through !!!
Glad you enjoyed it!
how about using object store for images, combined with DB for personal data?
Thank you! Is this right - for every request for the image, there are two requests fired - one for image path from either cache or DB, and one for the image itself from S3 after the first requests executes? Thanks.
@@BitBlastBroadcast Thank you!
Actually I think a write-through cache, or cache-aside to the write service will be easier to generate the feed. Bcs the cache server will know what content is pushed recently.
So will the objects themselves who are stored with time and location data. Any component dealing with those objects will have that data, not just the cache.
You want the use case to be “new to the user” not “new to the system” anyway.
hello, what app are you using for these sketches and notes? thanks great content!
Thank you for this video, this is awesome. BTW which app you are using for designing the system?
It’s called Whimsical
Can someone let me know which whiteboarding tool is used in the video please? Seems very useful!
Should client be calling to web server before the app server? App server handles business logic, web server handles the user's requests
a deep dive into the feed service would be greate. because obviously thats instagram's core feature
Why was the choice RDBMS and not something like a GraphDatabase as it makes more sense for querying on larger scale
so as I understood there is one DB without shards or replication. The question that bothers me is how many simultaneous requests one DB can handle? and one more thing is how data would be freed from cache? and what size of cache are you expecting to have?
This is great. The feed if generated in an hour it seems slow. Could you do it when a followed person updated 500ms ago?
500ms is too short. There are too many mappings, you even cannot finish the update within 500ms. (i.e. if the update has not finished, how can you start a new update). For huge data cache syncing, usually we would do database sharding and have multiple threads to update each category separately. This will boost the total speed. As for the updating time, it really depends, it could range from 1min - 1 hour and even 1 day (like billing information). But 500ms is totally unnecessary. As a user, can you feel any difference between 500ms and 10s? No. But it is a huge diff in CPU & RAM perspective, 10s = 500ms * 20 times!
Good video, it would help if you can include rest interfaces (not in great detail, but something) as well in the future. A bit more diving into depth would help.
Hi, great video, what tool did you use for the virtual whiteboard ?
Also Amazon S3 is not a distributed file system but a key-value DB.
Whimsical
Actually, Amazon S3 is indeed a distributed file system (or an object storage, as Amazon likes to put it) and not a key-value DB. Amazon uses its DynamoDB service for key-value storage.
Once the endpoint URLfor the image is figured out by making the search in MetaData DB, would a new request fire of again through the client to get that image through S3 or CDN? Or would thius happen in same request, as in we have an additional MicroService which would make a call to S3 or CDN and give back the image in same req?
Hey @Ritesh Thombre! Typically the client will receive the first response from the web server, then make separate requests to the CDN for the image/video assets. This allows the client to optimize when to load these images for the best performance (e.g. when scrolling)
@@tryexponent Agreed. I guess, just a thing about design choice. Ours is a mini banking application and we make search of a customer's eStatement through its Metadata, get the DocID and generate the URL. Then hit the cloud storage and give back the document in same request.
What you are proposing looks like will add another network call but that's fine. I think its a matter of design choice.
Love this!!!! really!!!!
Very helpful - Thank you.
Its nice, thank you !
1. CDN could have been added
2. Encoding of videos and photos
what is the difference between load balancer and cdn? I guess both of them are for loading faster, distributed?
Great video, really helpful.
Hi! Why not explore Hybrid database implementation using RDBMS and NoSQL databases? How would this system handle the bottlenecks when start scaling? What would be the response time? Also, implement queues between the cache and the database could help. It's a clean implementation, great quality, it's a possible approach.
Hey Gustavo! Good questions. In a sense, we are using a hybrid approach with a relational database plus a key-value store like Redis, but you could use other types of RDBMS and NoSQL systems, too. In reality, Instagram uses Postgres + Cassandra, with some advanced indexing and sharding strategies which you can read about on their blog! Let us know if that helps! instagram-engineering.com/handling-growth-with-postgres-5-tips-from-instagram-d5d7e7ffdfcb
@@tryexponent i think i came across the same article in my own research. totally agree.
Nice solution, definitely deserve an Amazon SDE II.
Should we not consider a async queue before uploading to S3?
Thanks for sharing this amazing knowledge.
I could not understand whether the generated feeds are stored in the cache based on each user or not. Because I think, storing feeds based on each user, causes Cache faces lots of hits.
Very nice video. What is the tool you used in the video? Looks pretty slick and easy to use.
Don't you need to use a CDN for the s3 distribution of images?
Excellent explanation.
Cool really liked it thanks a lot
Do we need to explain data modeling also?
Seen first time in system design.
In what cases I should be presenting database modelling and what cases I shouldn't?
You almost always have to do some data modeling, which isn't too difficult. I would assume you need to do it unless the interviewer interrupts you and says you don't need to. Usually, in system design, you are supposed to be driving the interview once you clarified the features.
What tool are you using to sketch out the architecture?
Excelent video , Could you tell me what is the tool you are using for drawing?
Hey great video Jacob learned a lot. Really liked the way you explored everything giving fairly reasonable and convincing solutions . Thanks for the video again really appreciate the effort.
Thanks Kapil! If we had to make another video next, what should the topic be? :)
@@tryexponent Typeahead Suggestion or Twitter Search would be interesting topics .
An excellent video and the way of presenting. I have a question, though, about the diagram. The connection between the database and the object storage seems not to belong there, as the database doesn't care what file path it stores.
Hey @Yan, that's a good point - there's no direct dependency between these two components, but we wanted to illustrate that the file path is referencing the object storage in this case
Nice one. The connection between the metadata DB and the Cache got me wondering if it's possible to have a database trigger that actually updates a cache when data changes
Actually there will be a cache miss and then cache will go to the DB to get the updated data.
well explained, which software are you using?
Whimsical! whimsical.com/
Is it good to ask to interviewer whether they are looking for App development on Premises or cloud? what would you suggest?
Hey Vivek! We would recommend focusing on cloud app development in general, but your overall architecture should be platform-independent. For example, here we point to using a relational database, but it could just as easily be a self-hosted one vs Amazon RDS or Google Cloud SQL. Does that help?
@@tryexponent Thanks. make sense
Is it good to cache feed as this changes frequently.
What tool are you using to write the requirements?
Well done, nicely explained
What would have changed had the requirements been web based vs mobile based? If any?
Hey Arturo! There are certainly some differences in web or mobile-focused application, however a good backend would work for several types of clients. We didn't dive into the mobile or web client here - would you like to see another video focused on of those?
what software is that you are using for the DFD?
What is the programme is used for here, i love it many thanks
Hey Ali! It's Whimsical
can you tell which tool you are using for designing in this video
Awesome video, thanks for that. Question: You have estimated a storage capacity of 1.2PB but still decided for a SQL DB. How does that align with our goal to build a scalable system? I was expecting a NoSQL choice here. Please correct me if I'm wrong.
Hey Ash! Thanks for the question. We should have clarified that this estimate is for the size of the images. The database would just store references (URLs) to the images, which can be stored in a storage system like Amazon S3 and served by a CDN.
@@tryexponent Thanks for the clarification, that makes sense.
it is still makes more sense to go for NoSQL DB for scalability
I have a similar doubt too. Even if we ignore the size, is relational db scalable enough for this kind of problem?
Liran elisha this would not be sufficient - scalability is not one dimensional. You can read the actual story about how Instagram originally did it at High Scalability. There is a cost to using NoSQL - schema on load versus schema on read. If you care about data integrity and operational familiarity, it’s hard to beat SQL. These are considerable trade-offs worth sharing and discussing during an interview. It’s not blatantly obvious why some hand-wavy NoSQL solution is more scalable. Which part? I don’t doubt that there is a NoSQL solution that makes some bottleneck in the system much more performant, but rather we should go with a choice and be able to defend it and also discuss alternatives and their trade-offs