Work in a real project · chapter 9 of 17
Small and reversible changes
A safe change has a known baseline, a bounded objective and a tested recovery path that does not overwrite someone else's concurrent work.
9.1 · plain explanation
How do we deliver visible progress without making production difficult to recover?
A safe change has a known baseline, a bounded objective and a tested recovery path that does not overwrite someone else's concurrent work.
Important: A backup does not make a change reversible if restoring it would erase unrelated data created after the backup.
9.2 · building blocks
Three concepts to keep separate
Preflight
Confirm the target, owner, current state and that assumptions still hold.
Recovery
Capture an exact bounded backup or use version history before mutation.
Guarded rollback
Recovery first checks that the active state is still a version known to the release.
9.3 · method
A practical workflow
- 1Measure and checksum the baseline.
- 2Build the smallest coherent change.
- 3Rehearse apply and rollback on a copy.
- 4Publish atomically and roll back automatically if acceptance fails.
9.4 · concrete example
One CSS defect
One CSS defect
How do we deliver visible progress without making production difficult to recover?
An empty WordPress paragraph occupied the grid column and made the text 220 px wide.
A single selector was tested at four viewports, deployed with a file backup and checked against exact content and SEO hashes.
9.5 · try it yourself
Exercise
Choose a small change and write preflight, apply, postcheck and rollback as four separate idempotent steps.
9.6 · checklist
Before you continue
- Is the current state measured?
- Is the backup bounded and readable?
- Could rollback damage concurrent changes?
- Does a critical test failure trigger automatic recovery?