Cheat sheet & self-check

Pick an answer to see if you got it, and why.

1. Q1. Where should a CLI write its data and its log messages?

   1. ABoth to stdout
   2. BData to stdout (so it can be piped), logs and errors to stderr
   3. CBoth to stderr
   4. DTo a file only
   Show answer

   B. Keeping them apart lets `kaudit nodes | jq` work while warnings still reach the terminal.

   From lesson 04 · Building command-line tools

2. Q2. Why use signal.NotifyContext in a CLI?

   1. ATo print colours
   2. BSo Ctrl-C or SIGTERM cancels a context that every operation uses, and the tool stops cleanly
   3. CTo read flags
   4. DIt's required by cobra
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   B. HTTP calls and loops that honour the context stop promptly and can clean up.

   From lesson 04 · Building command-line tools

3. Q3. Why is http.DefaultClient risky in a CLI or service?

   1. AIt's slow
   2. BIt has no timeout, so one stuck server can hang the program forever
   3. CIt can't do HTTPS
   4. DIt doesn't support JSON
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   B. Create your own client with a Timeout, and use contexts for per-request deadlines.

   From lesson 05 · HTTP, JSON and APIs

4. Q4. Which failures are usually worth retrying?

   1. A400 Bad Request
   2. BNetwork errors, 429 Too Many Requests and 5xx responses, with backoff and a limit
   3. C401 Unauthorized
   4. D404 Not Found
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   B. Client errors won't fix themselves; transient server and network errors often do.

   From lesson 05 · HTTP, JSON and APIs

5. Q5. You need to check 500 clusters in parallel but at most 20 at a time, stopping everything if a fatal error occurs. What fits best?

   1. A500 goroutines with no limit
   2. Berrgroup.WithContext with SetLimit(20)
   3. CA for loop with sleep
   4. DOne goroutine per cluster and os.Exit on error
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   B. errgroup bounds parallelism, collects the first error and cancels the shared context so the other tasks stop.

   From lesson 06 · Concurrency you'll actually use

6. Q6. What is a goroutine leak?

   1. AA goroutine that uses too much CPU
   2. BA goroutine blocked forever (e.g. sending on a channel nobody reads), never exiting and holding memory
   3. CA compile error
   4. DA closed channel
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   B. Leaks build up silently in long-running programs; contexts and buffered or closed channels prevent them.

   From lesson 06 · Concurrency you'll actually use