Cheat sheet & self-check

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

1. Q1. Why use informers instead of calling List every few seconds in a long-running tool?

   1. AInformers are required by RBAC
   2. BInformers list once, then watch for changes and keep a local cache, so reads are cheap and the API server isn't flooded
   3. CList is deprecated
   4. DInformers are faster to write
   Show answer

   B. Polling with List from many tools is a classic cause of API server load; informers are how controllers stay efficient.

   From lesson 07 · client-go: talking to Kubernetes

2. Q2. Why is a patch usually better than Get-modify-Update for changing a label?

   1. APatches are encrypted
   2. BA patch sends only the change, so it doesn't overwrite fields another client changed in between (and avoids conflicts)
   3. CUpdate is not allowed on nodes
   4. DPatches skip RBAC
   Show answer

   B. Update replaces the whole object and fails or clobbers on concurrent changes; a merge patch touches only the fields you send.

   From lesson 07 · client-go: talking to Kubernetes

3. Q3. What must every reconcile function be?

   1. AFast at any cost
   2. BIdempotent: running it again with the same state changes nothing, because it may run many times for the same object
   3. CCalled once per object
   4. DWritten in YAML
   Show answer

   B. Reconcile runs on every relevant event and on resyncs. It compares desired with actual and only fixes the difference.

   From lesson 08 · A small controller with Kubebuilder

4. Q4. What is a finalizer for?

   1. ASpeeding up deletion
   2. BLetting the controller clean up external things (outside Kubernetes) before the object is really deleted
   3. CEncrypting the object
   4. DStopping garbage collection of child objects
   Show answer

   B. Objects in the cluster are cleaned up by owner references; finalizers are for anything else (cloud resources, DNS, external systems).

   From lesson 08 · A small controller with Kubebuilder

5. Q5. How do you test code that calls an HTTP API without the real API?

   1. AYou can't
   2. BStart an httptest.Server that returns canned responses, and point the client at its URL
   3. CMock the network card
   4. DOnly test in production
   Show answer

   B. httptest gives a real HTTP server on localhost, so the client code is tested as it runs.

   From lesson 09 · Testing, linting and shipping

6. Q6. Why build with CGO_ENABLED=0 for container images?

   1. AIt's faster to run
   2. BThe binary has no dependency on the C library, so it runs in scratch or distroless images and on any Linux
   3. CIt enables TLS
   4. DIt's required by Docker
   Show answer

   B. A static binary needs nothing from the image, which keeps images tiny and the attack surface small.

   From lesson 09 · Testing, linting and shipping