NALSD Interview

Here are Mico Maco’s steps / points to remember when doing a Large Systems Design interview.

Questions and assumptions

• Do questions and explain your assumptions to clarify scope of the desired target system
  • geolocation of users
    • is timezone a factor to be considered?
  • amount of data transmitted (is not the same a 125 char tweet than a photo upload)
  • # of users and amount of requests per user
  • transmitted data and # of requests, think about data messages format
  • SLI, SLO and SLA of service

Start high level

• Start design with a simple high level design

  user <–> web server <–> database

Its all about data

• Its all about data:
  • transmitting, storing and accessing data
  • reads vs writes
  • select the database model (Relational?, Key-Value?).
    • Think (high level) about CAP, transactionality (ACID).
    • Might help a combination of several DB/models?

Initial API

• Some comment about an API?
  • REST, CRUD

Refine with tools

• Refine design with tools
  • cache –> comment on rendezvous or consistent hashing or
  • proxies –>
  • load balancing –>
  • data sharding –>
  • Consensus –>

More tools

• Add more tools !!
  • Metrics and monitoring
  • Change management? Deploys?
  • Recovery from failure

Bill of materials

• At the end, explain the bill of materials of your design
  • Compute (Web server, app server, DB server, …)
  • Permanent storage (disk)
  • Volatile Storage (RAM)
  • Network