System Design

  • — What is System Design?
    • — Deciding on the servers in a backend system and how they communicate
  • — Load Balancing
    • — One server cannot handle all request when traffic is high
    • — Load balancer receives the request and sends to the
    • — Some situation require stickiness
      • — Same client always has to connect to the same server for a session
        • — Load balancer with a good cache algorith can do that based on inputs
      • — If it is possible to avoid this, the better
        • — Can use JWT reduce the need for server state
  • — Cache
    • — How they help?
      • — Reduce database queries which require disk access and
    • — In Memory Caches
      • — Redis
    • — Cache policies
      • — What to throw away when cache is full
  • — Database scaling
    • — Sharding
      • — Separate data based on certain fields. And putting in different servers
      • — Not always possible to cleanly separate if there are dependencies
        • — Possible ways to separate are user, tenant, region etc.
    • — CAP theorem
      • — When you want partition tolerence, (which is always), you can either have availability or consistency
      • — Eventual consistence is accepting brief periods of stale data
      • — Consensus algorithms
  • — API manager
    • — Multiple functions
      • — Security checks
      • — Presenting client end points and access multiple services for tha
      • — Rate limiting and user procing
  • — Event bus
    • — Decouplesd ways to have multiple servers keep in sync
    • — System can put post events and move on to other ways
    • — Events are stored safely in database until they are delivered
    • — Event sourcing based data modeling
      • — Immutable events are added
      • — State can be derived anytime and if lost
  • — CQRS
    • — Fanout
      • — Data is stored in one database and what is needed for the view is put in another database
      • — Social media posts are parts of write database and read databases handle news feed
  • — Failure handling
  • — Notifications systems
  • — Chat systems
    • — Need to keep live sessions
      • — Call web server to get a URL to the live server, then connect to that