You can watch more system design videos here: interviewready.io

Hi Gaurav, I have been a developer for 43 years and a system architect for 30. As a very experienced professional all I can say is: good work ! You are the real deal.

occasions like good morning in India putting a lot of pressure on the servers🤣🤣

I learn more on KZfaq than school !!

This was great. A minor nitpick, this is not what peer to peer means although it can be confusing. Peer to peer would mean apart from one time registration, the connection never touches your server and instead is established directly between 2 clients(friends on whatsapp). Also HTTP now has server push and whatsapp actually uses XMPP(slightly modified).

well narrated and presented. never knew whatsapp and tinder has so much thing at backend. interesting when you ask someone for a coffee. and she accepts the coffee invitation. both are important sugar in coffee and web sockets and the micro services. lol. Hats off. truly brilliant .

I don't know anything about system design or even what it is, yet I clicked the video and watched it full. Just understood everything, great teaching skills :)

12:43 Now I understand why my gf would still show online for sometime even after we have sent goodnight messages. 😂😂

One thing I really like about your video is that you always tried to explain things from the client side, which makes it highly understandable for us as clients in our daily life. Thanks for your video!

KZfaq recommendation, thank you so much for this gem

Great video, this kind of stuff is not easy to learn and not enough resources out to explain. Thank you for your great efforts

These videos clearly shows how far away are university syllabuses from the real-world problems

I watched other videos on messaging systems and this video has a very detailed approach, I was hunting for videos just to know how to have multiple servers for socket processes when the client is a mobile app and I feel this video has helped me a lot with that.

I really amazed by how good you are at explaining complex concept in such a simple way. I can just keep watching all your video. Great job! ❤️

Age and experience doesn't matter to achieve, you proved it bro

i'm interviewing this week for systems design for the first time in my 6 year career. this isn't part of my job. but here i am, learning an irrelevant (to me anyway) skill to be better at tech interviews. thanks for sharing!

I really like the way he smiles and teaches. I know nothing about systems but that smile alone made me comfortable to watch the video......keep the same passion my friend......

Dude! As a beginner, I'm mind blown! Subscribed!

Hey man, nice video, but there's a mistake: long polling is not polling every minute to get updates. Long polling is when you keep an HTTP request open (think: spinner in Chrome while the page is loading) forever, until the server decides to respond. This in effect makes it near real-time. It's one of the ways websockets work.

Nice, I like the fact that you put links to other videos for reference, this makes it easy for the audience.

Yours are some of the most helpful videos I've come across. Thank you for doing such a wonderful job.

Yet another great video on system design! Keep up the good work, also now I can watch in 1080p YAY!

I have hit the like button. I have subscribed. You are awesome!. So happy I found your channel.

I found your channel randomly and I was so grateful, thank you so much.

Great job as always! Thank you for actually enjoying what you are explaining.

You're really underrated in the developer circle. People need to watch all this a lot more than programming basics.

QQ: if you try to keep gateways light and delegating all complicated logic and memory usage to other services, you will still have to scale them per number of users/messages. So either there should be some discussion around batching between gateway and sessions or you can just scale the number of gateways and keep some logic there (for example parsing).

Great work!!!! Many thanks for putting all this together, Gaurav!

Hey, just wanted to clarify a bit about long polling. Long polling is actually more of a request from the client to the server and instead of the server returning a response immediately, the server is waiting for a change of some kind, and when there is a change, the server returns the response finally to the client. It was more common back in days before Websockets were introduced and adopted by browsers around 2011 roughly.

interview: "ya I'd have a lst seen microservice". Reality: "ok just add that as a function in your monolith we don't have time for a new service"

This video is awesome! Hoping I can find a good job after months of watching ur videos again and again! Thx! U r amazing!

Wonderful video which covers all the technical concepts involved. This is incomplete without any resource estimates like storage/bw and what kind of stores to use like a Key/Value store like etcd will work etc.

Kudos to you Gaurav. Your contents are always easy n straight forward to grasp. Thank you for making life better

Hi Gaurav , fantastic architecture design and explanation . But, for group massaging, "session" micro service is calling another "Group" micro service , which is kind of http chaining and potentially example of anti-pattern. Can't we implement messaging mechanism like "distributed Kafka" to make it more decoupled. Just a thought of mine. Let me know your take on this.

Amazing content, kudos from Brazil !!!

I only had one or two serious system design interviews till now and the face expressions of the interviewer really put you off sometimes. I have never seen anyone explaining system design like this, it's good to know that I'm not very far off.

I'm from a non technical background and this video was super helpful and clear. On a side note, "Check with your doctor if group messaging is right for you" - hilarious :'D

Hey Gaurav - thanks so much for putting up such quality content! You're truly a wizard.. I've been learning so much about system design purely from your videos. I was wondering though, where exactly should I be placing the message queue in this example? Would it be after the sessions microservice confirms with the group-service which users are part of the specific group that the message is directed towards?

dude you are the man.

Excellent stuff buddy. Very useful. Keep up the good work.

Found KZfaq recommendations today. Great video indeed.

thanks for the amazing contents, brother.. another topic suggestion is system design for payment processing system like venmo or paypal

Great video! About the 'last seen' feature: I don't think the Last Seen is based on the last activity (e.g. sending a chat) but rather when the user closed the connection to whatsapp. So in my opinion, as soon as 1) the network is interrupted or 2) the user closes the application, the 'last seen' should be updated.

Really like your videos. Keep up the good work . Cheers !!

Thankfully I came across this channel. Really awesome videos and explained in easy way. Keep up the great work!

This is just that amazing video I was looking for. Regarding de-priotising, there is this feature called broadcast messages in whatsapp which I presume is used to send messages like "happy new year" etc. Can you tell me if I am right?

Great Video, Helpful !! I feel the 'Last Seen' feature could be improved (based on the steps described in the video). The only shortcoming I see with the current approach is, 'What if the user replies a message (i.e an action taken by the user) from the notification directly without opening the application !!'. One approach could be if a flag is sent in the request { 'fromNotif': true } that could be used to determine to decide if the Last_Seen table needs to be updated. Another could be to use the WebSocket connection itself and using the disconnect callback (once the user gets out of the application, the WebSocket connection can be disconnected). Push Notification can be used to update the message count once the user is outside an application and more approaches could be formulated further. Nevertheless, your video does help for beginners in system design.👍

Great video brotha.. @gauravsen. Nice work you're doing thumbs up for that. Hope we had lectures for these topics and lecturers like you🤗

Thanks, this is good session for UI developers also to understand on high level how chat system works.

How does Telegram can function having lakhs of members in each group?

Good work. There are a few important topics worth covering though. 1. What happens to a message sent to an offline user. 2. What choices of storage do we have ? 3. What kind of load + image/video messages ?

I'm happy that I know what the most important part of programing is which is what you just showed, and not the writing part. It's the pen and paper part that matters. This really satisfies my superiority complex

Making educational video in a happy mode desires a big thumb up!

Thank you Sir. I moved from India to San Antonio as new college grad. Amazon offering me 500K per year. Excited. Thanks for video.

You did a great job of listing the microservices and interaction between them. One thing which I would like to know more is the database design. How do we maintain a system with so many chats each with thousands of messages growing over time.

KZfaq is such an amazing platform. Thanks for the video

Brilliant communication skills and very good English accent... great job keep it up

Your system design videos are excellent! very easy to understand when comparing to others. It would be great if you explain multiple recursion(more than one recursive call in a function). I've reffered some online resources but It looks more confusing. I know you could make it easy to understand :)

I love you man, I used this to get an offer in my interview today.

Hi Gaurav, Thanks for sharing videos on system design. You explain very well. God bless you and keep sharing such great videos.

7:40 what you describe here is just regular polling. long polling does indeed operate on a near real-time basis - the connection is held open and the server can respond to the client in real time. the difference between long polling and web sockets is that with long polling you have to drop and re-establish the connection after the client receives data from the server, since this terminates the connection. whereas a web socket stays open indefinitely.

Great video brother...There seems to be fluctuations in the room lights where in you're recording... Subscribed

Great!Thank you. Next topic should be "Service discovery"

Amazing explanation. Subscribed!

And here I am, looking at some guy teaching IT things I should probably know already... Thanks :D

Good video! Would have liked even more if you had included following points as well becuase I felt lost there. 1. How does the gateway manage the TCP connections for each user? Is it in memory or in external store? What happens to the clients connection and messages when the gateway goes down? 2. How does the session service talks to gateway? Is it using RPC or message passing etc?

I wish there was a 100 like button for the video, thanks Gaurav. You've been an inspiration for me in cracking Amazon in 2018 placements. :)

YT: Here's a nice video on chat system design ME (first impression): I love your shirt. Now, let me enjoy the video.

Thanks Gaurav. Nice explanation.

Hi Gaurav, Great video few suggestions; 1. Keeping too many gateway would kill you latency [or may be I'm overthinking] but if we have some services which basically authenticate and establish the web socket connection, there after other services which work as mediator and communicate back-n-forth with client then we can simply reduce the number of gateway we need. [ essentially the gate would do this, but we don't need as many gateway as client are there; imagine 50 million clients at a time on whatsApp] 2. We should not stick with only push mechanism, where you said that "server will keep trying to to send the message to B" instead here it should be pull technique should be use. What I. mean is, once a user successfully establish the connection to Chat server, it AsK "do you any thing for me" and server response back (through queue technique so that message order are persisted ) and then after its all push technique until same thing happen for different user This way we keep server doing less and redundant work, to keep checking. Again think about 50 million user there. on Percent, 0.01% [5K users at least] of them chat each other. then there would be very high number of user might not be online, and for that server keep trying. 3. We don't need to keep checking in server database for where the user is, we should cache them. That may be 50 million entries at max at a time. As soon as the user goes off, remove him [ make sure the app should send the right information, don't send that when user just stack the application and will come back in a minute or so. it should be only when there is no internet connected.] In the essence, the connection would be of two types {1. active 2. ideal- help to build last seen too} when connection is ideal, we can utilise the connection for other chat and as soon as the user receive a message then we'll either create a new (if that connection goes off) or use the same. This is trade off you see, making a new connection is costly but keeping lot of the ideal is also poor. incase , if we mark offline the user who is connected to internet, we'll lost real time communication.

Nice Video! Regarding authentication though, most of the applications in the real world rely on client directly calling the authentication service, get a valid token(JWT?) which can be used by other services before responding. This avoids the extra parsing/un-parsing hop between gateway and sessions service.

This is a good explanation from the sessions micro services perspective. But one area you need to expose a bit more is client caching.

Thank you Gaurav, you cant imagine how much this video helped me last year.

Having sat in FAANG interviews both as an interviewer and as a candidate, I can say that this is not going to hold up for someone interviewing for a senior position.If you have less than 5-7 years of experience, you may get away with some hand waving, but for 10+ years, we want to see more depth. Some of the users have already brought up questions like delivery of offline messages, which is a basic feature missing. Apart from that, there are some crucial things missing in this video: 1. **API**: You want to discuss basic API (like REST) design, verbs supported, payload etc. You don't need to spend 30 minutes creating a JSON schema, but mention the endpoints and what's being sent and received. This matters for latency, and for some advanced things like security, API versioning, bandwidth usage etc. 2. **Back of the envelope calculations**: This is important for scalability, availability and storage. How many daily active users? Is there a limit to the message size? (you probably don't want people dropping 5 GB pirated movies in a group). How many gateway servers do you need? How long are the messages stored? Do you need to shard the DB? What is your partition key, and how do you deal with hot partitions? 3. Most importantly, **offer alternative design options and discuss trade offs**. If you can only talk about one thing, then you most likely learned it from some blog/video/whatever. There's no perfect solution in system design, so, we want to know you can think out of the box, and why you are choosing to go one way or the other.

Hi Gaurav, I have one query : How will database keep re-trying? Should we use message queue here instead of DB?

Great video Gaurav , really makes sense when it's broken down . I would say one key takeaway at least for me is that whenever a specific microservice/ component has too much on it's plate to handle you delegate that additional burden to another microservice. Wish people could be like that sometimes in real life😂

well done !! you made it really simple to understand

@Gaurav: Man I envy you, you are a gem explaining the complex things. I have 1 basic question: As we are using websockets for communication, don't we require not million but thousands of servers to connect billions of users ?? If you can help me understand this part can help a lot.

A critical piece that I feel is missing here is delivery of messages when the user is offline. You might not have an active connection to all users at all but you do need to deliver all the messages that were sent to them once they are connected.

Great one! Thank you for these videos. I'm in class 11 now, and I learn a lot from these videos.

Within first five minutes of the video I figured it out, this is going to be a real informative video and subscribed at the end. Great job!

I'm not into programming, though I appreciated this video. I'd really like you to publish a similar lesson, but for Telegram. Thanks in advance, and keep up the good work.

Hi @Gaurav Sen This is very good session. Just wanted to ask, If use MQTT instead of web sockets. Does the native support for publish/subscribe would bring any advantage for the chat application?

damn... you're fast draw/handwriting is great.

Nice Gaurav, I really enjoyed. Thank you so much.

Great Video, Really liked this one...!!! Just wanted to ask that for the last seen timestamp wouldn't it be better if the client sends a request(Or should I say message!) to the server when the user exits the messaging app(maybe when he exits the main app activity)., Wouldn't it save a lot of overhead for the last seen timestamp(Not taking into consideration the online stamp)?

Hi Gaurav!! Thank you for educating me with all your awesome videos! I have a request for a video! Can you talk about building a cloud-native system? Things like what's the benefit of using cloud and where we should be careful when designing a system. Also, as Hadoop is dying recently, I feel like some of the solutions are out-dated. For example, HDFS and HBase won't be a good option anymore as they require Hadoop cluster.

Bang on! the tech depth, the teaching style. extra +1 for making the learner think. Great video. Thanks Gaurav

Hey, man first time watching your video but just want to say your explanation is awesome. Appreciated!

Great video, Gaurav! Chapeau! I was wondering why the messages are stored in message queues. Why not a low-latency publish&subscribe mechanism? I would think a persistent event stream (e.g. Kafka topics) yields a simpler architecture for this particular use case. Just give each user group a Kafka-topic of its own. Now WhatsApp has smart software engineers on board, so I'm wondering what they have done to compare these two (MQ vs. Kafka) and why it turned out to be an MQ-architecture.

After watching this.... I am highly interested in system design

This man is a legend!

Thank you so much, it is a very useful channel.

Would be great if you have another video to break it down feature wise and why these were the final choices in terms of languages/tools/concepts used to implement all this. Maybe helpful for people coming from non-backend development

great stuff man, -16 yr old Keep making such vids :)

Thank you so much for the video. The best part I liked is, you asked us prior, which is the next video to be uploaded. Thanks again. Just take care of voice modulation in the video next time :)

Gaurav, this is tremendous help, keep up the great content. I subscribed :)

Thanks for your effort! It's great to learn lots of things from your video. But I still have a question after watching this video. Why consistent hashing can help to reduce duplicate information (on 20:57 explaining the group service)? Isn't it just a way of knowing which record should be found on which server?

nice super, and shirt like good professional look

Thank you so much Gaurav, all of your videos are very helpful.