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Learning Paths

Backend & System Design

Build services that stay up: HTTP and APIs, data and caching, distributed systems, reliability and security, and the design interview that tests all of it.

Finish this and you can design a service for millions of users on a whiteboard, defend each choice, and build a smaller version that actually runs.

Starts at
Intermediate
Topics
5
Projects
5
Of material
101 h
  • APIs
  • Databases
  • Caching
  • Distributed systems
  • System design
Level
Format
  1. 01

    HTTP and API design

    Beginner

    How the web actually talks, and APIs other teams can rely on.

    Build this

    A URL shortener with a real API contract

    Small enough to finish, rich enough to design properly.

    1. Write the API contract first (OpenAPI), including errors and rate limits.
    2. Implement it with a relational store and idempotent creation.
    3. Return the right status codes and cache headers for every route.
    4. Deploy it and share the docs page.

    Done when: A deployed service with its OpenAPI document and tests.

  2. 02

    Data, indexes and caching

    Intermediate

    Choosing a store, making queries fast, and caching without serving stale nonsense.

    Build this

    Make the shortener fast, then prove it

    Add a cache to the URL shortener.

    1. Load-test the redirect and record p95 latency.
    2. Add a read-through cache with an expiry you can justify.
    3. Handle invalidation when a link is edited or deleted.
    4. Load-test again and explain the difference.

    Done when: Before-and-after latency and a note on the invalidation design.

  3. 03

    Distributed systems

    Advanced

    Replication, consensus, partitions and the trade-offs behind every large system.

    Build this

    Implement Raft leader election

    Do the first Raft lab from the MIT course.

    1. Read the Raft paper before writing code.
    2. Implement leader election and pass the lab's tests repeatedly, not once.
    3. Write up one bug that only appeared under the test's network faults, and how you found it.

    Done when: Passing tests across a hundred runs, and the bug write-up.

  4. 04

    Reliability and security

    Intermediate

    Service levels, incidents, observability and the API security mistakes attackers look for first.

    Build this

    An SLO, a dashboard and a postmortem

    Run the shortener like a production service.

    1. Define two SLOs and the error budget they imply.
    2. Instrument latency and errors and build the dashboard.
    3. Inject a failure and run a blameless postmortem on it.
    4. Audit the API against the OWASP list and fix what you find.

    Done when: The SLO document, the dashboard, the postmortem and the security fixes.

  5. 05

    System design, the interview

    Advanced

    A repeatable approach to designing a large system out loud in forty-five minutes.

    Build this

    Three designs, presented out loud

    Practise the way the interview is run.

    1. Pick three systems: a feed, a chat service and a ride dispatcher.
    2. Design each in forty-five minutes, out loud, recorded.
    3. Review the recording against the primer and redo the weakest one.

    Done when: Three diagrams and notes on what changed after review.

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Backend & System Design · Learning Paths · CareerOS