DSA & System Design

System design · HLD path

High-level design, one stop at a time

10 steps from rough numbers to a full case study. Each has a diagram that plays, a widget to poke and a quiz to finish.

  • 10 steps
  • 5 h end to end
  • 2 case studies
1Requirements2API & load balancing3Databases4Caching5Queues & messaging6Consistency & CAP7Reliability8URL shortener9Notifications10PlaybookCase studies

Got a minute?28 one-minute shorts on the HLD path. One idea per card, swipe for the next.

Open shorts
  1. 01 25 min

    Requirements and Estimation

    Every design starts with what to build and how big it is. Numbers decide whether you need one server or fifty, a cache or a shard.

    Step 1
  2. 02 30 min

    Client, API and Load Balancing

    One server is a limit and a single point of failure. Stateless servers plus a balancer let you add capacity by adding machines.

    Step 2
  3. 03 35 min

    Databases and Scaling

    Data outlives servers and is the hardest part to scale. Choose storage by access pattern, then scale reads with replicas and writes with shards.

    Step 3
  4. 04 30 min

    Caching

    Memory is about 50x faster than a database round trip. A cache with a high hit ratio cuts latency and protects the database.

    Step 4
  5. 05 35 min

    Async Processing and Messaging

    Slow or unreliable work (email, video, payments) should not hold the user's request. Queues absorb spikes and let work retry safely.

    Step 5
  6. 06 35 min

    Consistency and CAP

    Copies of data on many machines can disagree, especially during network failures. You choose which guarantees to keep.

    Step 6
  7. 07 35 min

    Reliability and Observability

    At scale something is always broken. Reliable systems contain failures, degrade gracefully, and make problems visible.

    Step 7
  8. 08 40 min

    Case Study: URL Shortener

    A classic that exercises every earlier idea: estimation, ID generation, read-heavy caching, and storage.

    Step 8
  9. 09 40 min

    Case Study: Notification System

    Shows queues, fan-out, user preferences, deduplication, and external providers that fail.

    Step 9
  10. 10 20 min

    Interview Playbook

    Knowing the pieces is half the job. A repeatable structure shows seniority.

    Step 10