Diagnose six planted faults across the whole course

capstone · 160 min · Objective 6.5

Task

The final exercise. Plant faults drawn from every domain, leave them for a day, and then diagnose each by method under a time limit -- which is the closest a lab can get to the conditions the exam and the job actually impose.

Steps

  1. Write lab/cap6/faults.md listing twelve possible faults, at least one per domain: an oversubscribed host, a missing route, an undeclared dependency, an unattached volume costing money, a backup whose scope excludes new data, an over-broad policy, an unsigned image admitted, a non-idempotent consumer, a recursive trigger, a skewed clock, an exhausted subnet, and a console fix about to be reverted.
  2. Write a script that selects SIX at random and applies them. Run it, then close the laptop and come back at least a day later so you are diagnosing rather than remembering.
  3. For each fault, work the method in lab/cap6/log.md: scope it, state a theory before testing, record what you RULED OUT with evidence, name the cause, and record the elapsed time. Give yourself 20 minutes per fault before reading the script.
  4. For each, also record the PREVENTIVE control from earlier in the course that would have stopped it -- a guardrail, a check, a canary or a design choice -- and which objective it belongs to.
  5. Finally, implement the three preventive controls you rated highest, re-run the planting script, and record in lab/cap6/prevented.md which faults could no longer be introduced at all.

Verify

grep -Ec 'fault|round' lab/cap6/log.md
grep -Eci 'ruled out' lab/cap6/log.md
grep -Ec '[0-9]+ ?(min|minute)' lab/cap6/log.md
grep -Ec '[1-6]\.[1-9]' lab/cap6/log.md
test -s lab/cap6/prevented.md && grep -Eci 'could not|prevented|refused' lab/cap6/prevented.md

Six faults diagnosed with elapsed times, objectives cited throughout, and at least one fault that became impossible to introduce. That last file is the course's closing argument: detection is the weakest rung, and the controls that matter are the ones that make the wrong thing impossible.

Notes

The day's delay is the point of the exercise and the easiest step to skip. Diagnosing a fault you planted an hour ago tests memory; diagnosing one you planted yesterday tests method, which is what the exam's scenarios actually ask for.

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