System Design Interview

Wrap Up

Wrap up 1 min readLesson 4 of 4

In this chapter, we presented a design that supports a nearby friends feature. Conceptually, we want to design a system that can efficiently pass location updates from one user to their friends.

Some of the core components include:

  • WebSocket: real-time communication between clients and the server.

  • Redis: fast read and write of location data.

  • Redis pub/sub: routing layer to direct location updates from one user to all the online friends.

We first came up with a high-level design at a lower scale and then discussed challenges that arise as the scale increases. We explored how to scale the following:

  • Restful API servers

  • WebSocket servers

  • Data layer

  • Redis pub/sub servers

  • Alternative to Redis pub/sub

Finally, we discussed potential bottlenecks when a user has many friends and we proposed a design for the “nearby random person” feature.

Congratulations on getting this far! Now give yourself a pat on the back. Good job!

Chapter Summary

Reference Materials

  1. Facebook Launches “Nearby Friends”: https://techcrunch.com/2014/04/17/facebook-nearby-friends/
  2. Redis Pub/Sub: https://redis.io/topics/pubsub
  3. Redis Pub/Sub under the hood: https://jameshfisher.com/2017/03/01/redis-pubsub-under-the-hood/
  4. etcd: https://etcd.io/
  5. Zookeeper: https://zookeeper.apache.org/
  6. Consistent hashing: https://www.toptal.com/big-data/consistent-hashing
  7. OpenStreetMap: www.openstreetmap.org
  8. Erlang: https://www.erlang.org/
  9. Elixir: https://elixir-lang.org/
  10. A brief introduction to BEAM: https://www.erlang.org/blog/a-brief-beam-primer/
  11. OTP: https://www.erlang.org/doc/design_principles/des_princ.html

Finished reading?

Mark it complete to track your progress.

PreviousDesign Deep DiveNearby FriendsNext Understand the ProblemGoogle Maps