Shipping on Fridays

Don't deploy on Friday. It is one of those pieces of advice that circulates so widely it stops being examined, like drinking eight glasses of water. We followed it for two years at Passe, and I now think it made our software worse.

What the rule is actually protecting

The reasoning is sound on its face. Deploy Friday afternoon, something breaks at seven in the evening, and now someone's weekend is gone. Fair. Nobody wants that.

But notice what the rule assumes: that a deploy is dangerous, that breakage is likely, and that finding out takes hours. If all three are true, Friday is genuinely a bad day to ship. The rule is correct. It is just correct about a situation you should be trying to leave.

"Don't ship on Friday" is a reasonable response to a deploy you're afraid of. The interesting question is why you're afraid of it.

What we changed instead

Rather than defending Friday, we went after the fear. Over about five months we did four things, in this order, and the order mattered:

• Made deploys small. The median change went from a week of work to under a day. Small changes fail less, and when they fail the cause is obvious.
• Made rollback boring. One command, under ninety seconds, tested monthly. Not a runbook — a button.
• Made breakage loud. We alerted on the two things a customer would actually notice, and deleted every other alert. Signal went up because volume went down.
• Made it someone's job. One person on call each week, paid for it, with the explicit authority to roll back without asking anyone.

Only after all four did we drop the Friday rule. That sequencing is the whole point. Dropping the rule first would have been recklessness with extra steps.

The part I didn't expect

The benefit was not really that we could ship on Fridays. It was what happened to Monday through Thursday. When a deploy stopped being an event, people stopped batching work to fit around it. Changes got smaller everywhere, not just at the end of the week. The Friday rule had been quietly shaping five days, not one.

We still don't ship at five on a Friday. Nobody is around to watch it, and that is a different rule with a better reason. But the fear is gone, and the fear was the actual problem.