EO Engineering Learning OS
CORE FOUNDATION · F06
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NON-NEGOTIABLE FOUNDATION · TARGET L3 · 7 days
F06

Data & reliability

Operate state with explicit consistency, protection, availability and recoverability expectations.

01 / CONCEPT MAP

Know what the parts mean.

Learn each concept deeply enough to recognize it, place it in the system and reason about normal and failed behavior.

01

Relational data and schema

Define it · locate it · observe it · explain its failure mode.

02

Connections, pools and transactions

Define it · locate it · observe it · explain its failure mode.

03

Object, block and file storage

Define it · locate it · observe it · explain its failure mode.

04

Backups and restore

Define it · locate it · observe it · explain its failure mode.

05

Replication and availability

Define it · locate it · observe it · explain its failure mode.

06

RPO, RTO and failure domains

Define it · locate it · observe it · explain its failure mode.

07

Logs, metrics, traces and alerts

Define it · locate it · observe it · explain its failure mode.

02 / SYSTEM FLOW

Trace it end to end.

Application→Connection pool→Primary data store→Backup / replica→Restore process→verification

For every transition: identify input, output, identity, protocol, state, trust boundary, evidence and owner.

03 / GUIDED BUILD

Build, observe and explain.

Documentation and AI are allowed. The engineer must review every output and demonstrate the result from direct evidence.

  1. 01Document application state
  2. 02Create and verify a backup
  3. 03Restore into an isolated target
  4. 04Measure actual RPO and RTO
  5. 05Simulate connection exhaustion
  6. 06Add storage and database health signals
  7. 07Write a recovery runbook
04 / INCIDENT

The application is healthy but writes fail after the connection pool is exhausted.

Required investigation

State impact → collect evidence → form competing hypotheses → test the cheapest discriminator → isolate root cause → contain → correct → verify.

Evidence pack

Timeline, relevant logs/metrics, failed assumptions, root cause, correction, verification and one prevention action.

AI ownership

AI may suggest causes and commands. The engineer must explain why each check is safe, what result is expected and how the result changes the hypothesis.

05 / DESIGN CHALLENGE

Defend the decision.

Choose storage and recovery patterns for database rows, user uploads, configuration and logs.

06 / VERIFY, SUBMIT & REVIEW

Submission evidence

Architecture review

  • Explain data & reliability without relying on memorized commands.
  • Draw the flow and name what crosses every arrow.
  • Identify the most likely, highest-impact and hardest-to-detect failure.
  • Show the evidence that proves the solution works.
  • Defend one security, reliability and cost trade-off.

Definition of Done

  • Acceptance criteria pass
  • Flow is drawn and explained
  • Security implications considered
  • Logs/metrics checked
  • Failure is tested
  • AI output is understood
  • Runbook is reusable
  • Mentor review passes
07 / MENTOR GUIDE

Do not score memory. Score the engineer’s ability to form a model, collect evidence, make a safe change and defend the trade-off.

1 Cannot explain2 Understands with gaps3 Implements and troubleshoots4 Designs and reviews