"Never deploy on a Friday" is good advice for teams whose deployments are risky. It is worth asking why they are risky, rather than treating the calendar as the fix.
What has to be true
- The pipeline runs the tests, and the tests fail on real regressions
- Staging matches production closely enough to be evidence
- A rollback exists and has been performed at least once, deliberately
- Alerting fires on symptoms a user would notice
- One person can deploy without a checklist in a wiki
Rehearse the rollback
An untested rollback is a hypothesis. We rehearse it during the launch sprint on every project: deploy, roll back, verify, write down how long it took.
Once that number is known and small, the day of the week stops being interesting.