System Design foundations: check what you know

Already know some System Design? Answer these 11 questions, about 6 minutes. Each topic you get fully right is marked Known on the System Design roadmap, so you can skip it. Each one you miss is listed for you to study.

Don’t guess. Pick “I don’t know yet” when you’re not sure: a lucky guess would mark a topic Known that you still need to learn.

The 10 topics it checks

1. Client–server, HTTP and HTTPS
2. DNS
3. REST vs GraphQL vs gRPC
4. Latency numbers worth knowing
5. Vertical vs horizontal scaling
6. Load balancers: L4 vs L7 and algorithms
7. Caching: cache-aside, write-through, write-back, eviction, TTL
8. SQL vs NoSQL
9. CDNs
10. Back-of-the-envelope estimates

1. Question 1 of 11 · Multiple choiceA signed-in user tries to delete someone else’s post. Which status code fits best?

   401 Unauthorized403 Forbidden500 Internal Server Error201 CreatedI don’t know yet
2. Question 2 of 11 · Multiple choiceA page loads 30 files over HTTPS with a new connection for each. What helps most?

   Reusing one connection with HTTP/2Turning off HTTPSA faster CPU on the serverSmaller headersI don’t know yet
3. Question 3 of 11 · Multiple choiceYour DNS record has a TTL of one day. You change the address at noon. When have all users seen it?

   At noonWithin a minuteUp to a day laterNeverI don’t know yet
4. Question 4 of 11 · Pick the patternCalls between your own services, thousands a second, with typed contracts. Which style fits?

   REST with JSONGraphQLEmailgRPCI don’t know yet
5. Question 5 of 11 · Multiple choiceWhich is closest to one round trip across the Atlantic?

   100 ns0.5 ms80 ms5 sI don’t know yet
6. Question 6 of 11 · Multiple choiceYou add a second app server, and users’ carts empty at random. Why?

   Carts are kept in each server’s memoryThe database is slowThe load balancer is brokenToo much trafficI don’t know yet
7. Question 7 of 11 · Multiple choiceRequest times vary from 10 ms to 30 s. Which algorithm spreads them best?

   Round robinLeast connectionsAlways server 1hash(time) % nI don’t know yet
8. Question 8 of 11 · Spot the bugPrices are cached forever, with no TTL. What is wrong with this write?

   def set_price(product_id, price):
       db.update_price(product_id, price)
   

   It is too slowIt should write the cache onlyNothingIt never deletes the cached price, so the old one is shown foreverI don’t know yet
9. Question 9 of 11 · Pick the patternPayments must move money all or nothing. Which store?

   A SQL database with transactionsA key-value storeA search indexA CDNI don’t know yet
10. Question 10 of 11 · Multiple choiceHow do you ship a new version of app.js that is cached for a year, without anyone seeing the old one?

    Purge the CDN every hourSet max-age=0Give it a new name with a content hash, and link that nameAsk users to clear their cacheI don’t know yet
11. Question 11 of 11 · Multiple choice20 million uploads a day. About how many a second?

    202,00020,000200I don’t know yet

See my results

Answered 0 of 11.