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Fridays are the safest day for deployments

If you’re working on public-facing internet software – B2B or B2C SaaS or media, or anything really – Fridays are far and away the best day to deploy software updates to production.

This statement flies in the face of the guidance given by a large percentage of developers, believing that Friday deploys are somehow more dangerous or fraught than deploys any other day of the week.

But this isn’t true – or at least shouldn’t be true.

In my twenty-plus years of tooling around behind the scenes of the internet, traffic follows a familiar pattern – across SaaS and media alike. Traffic is highest on Monday, and then linearly declines until the lowest day on Saturday or Sunday.

The lowest weekday for traffic is consistently Fridays.

There is less load on servers, and for our purposes, much less attention paid to bugs and mistakes and errors deployed because there are simply fewer eyeballs on the work.

If we take for granted that any software deploy could have a bug in it (and I’d highly recommend taking that stance), deploying on Friday or the weekend exposes the least number of users to those potential bugs.

And Friday is typically a workday, while the weekend is, well, not.

The time with the absolute least blast radius for a deploy is quite literally as you walk out the door Friday afternoon.

That’s what my media days taught me as the “Friday evening news dump” period – when whatever bad news you had to disclose but didn’t want anybody to really notice gets dropped.

The same goes for software. Deployment on Friday when nobody sees the mistakes, marketing on Monday when everybody is paying attention.

“But that’s crazy!” I can hear you say. “When will we fix the bugs you literally just said would be there?”

There are tradeoffs involved. If you assume there will be bugs, you need to deploy on Friday with enough time to fix or rollback those bugs. So, unless the deployment is especially small, don’t deploy it literally on your way out the door and into the weekend.

“But what if the bug isn’t discovered until the weekend? I don’t want to work over the weekend!”

Neither do I. That’s why you make your deployments small – any day of the week, deploy them with a rollback plan in mind, and check your work when you deploy.

Then you can fix or rollback before leaving for a peaceful weekend.

Load-related bugs – which are bound to happen eventually – likely won’t pop up until the load picks up Monday morning. And guess what? Monday is another workday! You’ll be there to fix any bugs which pop up. Huzzah!

A lot of the “friends tell friends not to deploy on Fridays” advice comes from a good place – folks have lived through bad Friday deployment experiences that required some heroic, through-the-weekend experience.

This likely happens when you’re batching deployments – building up a large chunk of change to deploy all at once. There is a mismatch between the surface area for bugs and the time you have available to fix those bugs before the weekend clock begins.

To recap, for successful and fearless Friday deployments:

1. Keep your deployment small: This is a solid recommendation for any day which ends in “y,” but small deployments have by definition a smaller blast radius for the bugs they inevitably contain. This makes them easier to spot, test, debug and fix. This is critical to ensuring your Friday clock doesn’t run out before you can fix whatever pops up.
2. Know how to back out of the deployment: There is a clock on Friday. If a deploy goes astray, know how to pull the plug, revert to a known good state and take another swing at it on Monday with fresh eyes.
3. Check your work before you leave: Again, the assumption with any deployment is that there are bugs contained therein. Part of your job for any deployment, but especially Friday ones, is to find them and squash them before the business, your users, and your colleagues find them and before the clock strikes 5.

Remember: Fridays are the best day to deploy software to production … but probably not the best day for this essay to be published.

For the same reason: Nobody sees it on Friday.

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