How load balancers work - System Design Interview knowledge [Beyond the interview]

Knowing about how a load balancer works is important for most software engineers. Load balancing algorithms and techniques can be useful for your next system design interview too. Besides that, it quite interesting!

This video covers load balancing algorithms, how Google uses load balancing and traffic routing, a real word load balancing example for a web application, stateful load balancing and consistent hashing for load balancing.

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Music: Koalips
Music: Night Owl - Broke For Free
Music: Bensound

[SuccessinTech]

You all got it right, network is layer 3 in OSI. My bad! ;)

[yodude]

that purest contend I've ever seen in the Universe

[melihmtl]

I was just asked this question in an interview. Youtube recommended that video just after my interview. I wish I would have seen it before 😬

[yuganderkrishansingh]

3:27 IMHO is incorrect. It's not possible for two servers to run on same port unless the protocol is different. So two HTTP servers cannot bind to same port on a single backend server. The second HTTP server trying to bind to port will get the error - Address already in use.

[vadymmishchenko]

3:20 "both http servers on same ip and port" ? how is that possible ?

[sunny-]

What is difference berween L4 and L7 if both are routing based on clientIp, just that L4 maintains ip tables and L7 hashes client IP ? So won't both doing same thing eventually ?

[bzaruk]

Great video! thank you!! - one note though, and pls correct me if I'm wrong, two applications (servers) can listen to the same port at the same server instance as you mentioned 3:20

[JoyLong]

Network is layer 3 on OSI model, TCP/IP layer 4 is transport

[mohmedishak]

Late to the party but this guy is genius!

[MrMukulj]

How can two HTTP servers be running on the same backend on the same port 80 ? check out at time 3:15

[Sandermatt]

12:20 You say the hash function depends on the available servers. What if the same users connects again, but the available servers have changed? Will the user now be hashed to a new server, despite his originally assigned server maybe still being available.

Edit: solved later on in the video.

[jacob]

How to avoid single point failures? Replica with a master and slave model?

[diehardspidey]

Network is level 3? If I am not wrong ?

[hahmadzai]

Can you please make a similar video but for DNS?

[stoneshou]

Could you give hint on how spof is handled for lb?

[uttampankaj]

Great intro. Please make a video on how database work internally. How data is stored in database? Which data structures are used ?

[tacowilco]

What do you mean when you say that Front End take an RPC call?
This is confusing

[rafiresearchgroup]

How to avoid single point failures? I was also wondering what is the solution....

[PetrShypila]

Thanks for the video. Right now preparing for the interview. At the end you mention single point failure problem. What would be your suggestion on eliminating it? Just a quick thought is doing LB state backups/replica with a health checks so as soon as it crashes we could restart or quickly switch with a backup.

[RaviChandraEnaganti]

Going into details, how does the load balancer know the number of connections in each individual server? Where will this information be stored? at the balancer or the server itself? only a count of connections, or will they be stored as a queue?