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Diagrams as code for microservices

Draw systems by typing: architecture diagrams as code.

Write services and use cases as text. Proschi draws the diagram and plays every request through it.

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checkout.proschi 
title "Checkout"

web "Web Shop" [Actor]

group vpc "AWS VPC" {
  api "Order API" [REST API]   @orders
  db  "Orders DB" [PostgreSQL] @orders
}
events "OrderEvents" [Kafka] @platform

web -> api    : HTTPS
api -> db     : SQL
api -> events : publish

usecase "Place order" {
  web -> api : POST /orders json {"sku": "A1"}

  alt "Placed" {
    api  -> db     : INSERT order
    api ->> events : OrderPlaced {"orderId": "o-1"}
    api --> web    : 201 {"orderId": "o-1"}
  } alt "DB down" {
    api  -x db  : INSERT order
    api --> web : 503 {"error": "retry_later"}
  }
}

The editor, the diagram and the player load next.

Break it on purpose. Then test it.

Every alt is a way your system fails: watch the packet die at the database, not in production. Then check requirements, traffic and capacity in your browser. Green means it holds up.

Break it

usecase "Pay" {
  web -> api : POST /pay

  alt "Paid" {
    api  -> db  : INSERT payment
    api --> web : 201
  } alt "DB down" {
    api  -x db  : INSERT payment
    api --> web : 503 {"error": "retry_later"}
  }
}
The “DB down” scenario: the call from the Order API to the Orders DB gets no answer, and the API replies 503. REST API Order API PostgreSQL Orders DB 503

Test it

traffic {
  "Redirect" 100k rps mix "Cache hit" 90%, "Cache miss" 9%, "Unknown code" 1%
}

requirements {
  p99 "Redirect" < 100ms
  availability "Redirect" >= 99.95%
  survive any node failure
  cost <= 5000 usd/month
}

Tests URL shortener example 5 / 5 pass

  • p99 of Redirect < 100 msp99 of Redirect is 24.3 ms (limit 100 ms)
  • availability of Redirect ≥ 99.95%availability of Redirect is 99.999999% (limit 99.95%)
  • survive any node failureEvery use case keeps working after losing any of 4 nodes
  • cost ≤ $5,000/monthTotal cost is $3,000/month (limit $5,000/month)
  • Redirects are served from the cacheAll 6 assertions hold

For system design interviews

Interview prep roadmap

29 system design problems in 8 stages, from a URL shortener to ride matching. Each stage builds on the one before, the way interviewers expect you to reason.

  • Lesson Explains the concepts the problem needs before you start.
  • Challenge Design it hands-on; a simulation checks load, latency, failures and cost.
  • Review Feedback on your design: what holds up and what to improve.
Start interview prep

No account needed to start: browse every stage and work through the first one in your browser. Sign in if you want to keep your progress and go on.

The stages

  1. Foundations 5 problems
  2. Caching and the edge 3 problems
  3. Partitioning and replication 4 problems
  4. Queues and async work 4 problems
  5. Fan-out and real-time delivery 4 problems
  6. Streams and aggregation 3 problems
  7. Consistency and contention 3 problems
  8. Geo, media and hot spots at scale 3 problems

Practice system design

29 system design problems. Tests, not opinions.

All 29 problems

Arcade

Scale or Fail

The system design game: keep a system up while traffic grows, new use cases arrive and things break.

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