# Guided Exercise: Choosing the Right Workload Primitive

Paper-and-thinking exercise before the Labs.

## The scenario

Your team needs four things running in the cluster:

1. A nightly database backup that must run at 2am and finish before morning.
2. A log-shipping agent that must run on every node, including nodes added later.
3. A one-time script to backfill a new database column, run once during this deploy.
4. The main web application, always up, serving live traffic.

## Your task

For each of the four, name the correct primitive (Deployment, Job, CronJob, or DaemonSet) and
answer: what would go wrong if you used a Deployment for it instead?

## A worked answer to check yourself against

1. **CronJob.** A Deployment has no concept of "run on a schedule" — you'd need external
   tooling to trigger it repeatedly, reinventing what CronJob already does. Using a bare Job
   would run it once; CronJob is what recreates that Job on schedule.
2. **DaemonSet.** A Deployment's replica count is a number, not "one per node" — nothing
   guarantees even coverage, and a newly added node wouldn't automatically get a copy the way a
   DaemonSet guarantees.
3. **Job.** A Deployment expects its Pod to run forever; a script that's SUPPOSED to exit when
   done would be treated as a crash and restarted forever, which is wrong for a one-time task.
4. **Deployment.** This is the actual always-on, N-replicas case the other three are explicitly
   NOT designed for.

## Self-check

If you answered "Job" for #4 or "Deployment" for #1-3, revisit the lesson's decision table
before the Labs — getting this choice right the first time avoids building something that
technically runs but behaves wrong in a way that's easy to miss until it causes a real problem
(a backup CronJob accidentally deployed as a Job that only ever runs once, for example).

## Instructor Notes

**Facilitation:** Good as a quick individual exercise before revealing the answer — the "what
would go wrong" framing forces reasoning about the CONSEQUENCE of a wrong choice, not just
recall of a definition.

**Approximate timing:** 8-10 minutes live with discussion; 8 minutes self-paced.

**Optional extension:** ask what would need to be true for #1 (the nightly backup) to actually
be SAFE to run as a plain Job triggered manually once, instead of a CronJob — a good check that
students understand CronJob's value is specifically the SCHEDULING, not something inherent to
backups.