Domain 3 of 5 · Chapter 4 of 8

Configuration Management

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Included in this chapter:

  • Three states of one configuration
  • The baseline as golden reference
  • Version control and automated backup
  • Restoring after failure or a bad change
  • Exam-pattern recognition

The three configuration states: where each lives and what it is for

AttributeRunning configurationBackup (startup) configurationBaseline (golden) configuration
What it isSettings the device is using right nowSaved copy reloaded on next bootApproved known-good reference for the role
Where it livesVolatile memory (RAM) on the deviceNon-volatile storage on the deviceExternal version-controlled repository
Survives a reboot?No, lost unless savedYes, this is what reloadsYes, it is off the device entirely
Primary purposeRun the device liveRecover the same device after reboot/failureDetect drift, rebuild fast, enforce consistency
Updated byEach command as you type itSaving the running configApproving and committing a new known-good revision

Decision tree

Device failed or beingreplaced?Restore recent backupor deploy baseline onto itYesA change just brokeproduction?NoRestore last known-goodconfig; do not forward-fixYesGoal: every device samehardened state?NoDeploy from baseline(golden image)YesCompare live vs baselineto detect driftNo: catch changesAlways: restore from the backup, never rebuild from memory; test restores periodically
Cheat sheet

Cheat sheet

  • A configuration lives in three states: running, backup, and baseline
  • The running config is live in RAM and is lost on reboot unless saved
  • Save running to startup, or the change does not survive a reboot
  • A baseline is the approved known-good reference, changed only through change control
  • A backup is whatever was on the device; a baseline is the approved standard
  • A golden image is a baseline packaged as a full deployable template
  • Configuration drift is any undocumented deviation from the baseline
  • Secure config management runs establish, deploy, maintain
  • Version-control configs to get diffs and rollback to any revision
  • Automate config backups so a recent restore point always exists
  • Run version control and automated backup together, not one or the other
  • Replace failed hardware by loading the backup, not rebuilding by hand
  • When a change breaks production, restore the last known-good config
  • An untested backup is a guess; test restores periodically
  • Configuration management stores artifacts; change management approves changes
  • Infrastructure as Code prevents configuration drift
  • Declarative IaC states the desired end state, not the steps

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Also tested in

References

  1. NIST Glossary — Configuration Management Whitepaper
  2. NIST Glossary — Baseline Configuration Whitepaper
  3. NIST SP 800-128: Guide for Security-Focused Configuration Management of Information Systems Whitepaper
  4. What Is AWS Config? (configuration history and last known good configuration)
  5. AWS Well-Architected OPS08-BP03: Make frequent, small, reversible changes Well-Architected