re: Why you should deploy on Friday afternoon VIEW POST


You start off by comparing apples and oranges. A standard code release into production is more like a scheduled operation, walking into the ER is like applying an emergency hotfix. It's also fairly typical for hospitals to not have operations over weekends and last thing on Fridays for the same reason most developers don't release code on those times: there's not enough staff on hand to support those things.

You don't understand your system. You're making changes but you're not 100% sure it'll be OK. Ask yourself why this is. Why are you scared of changing your software?

I think it's unreasonable to expect any single dev to understand 100% of a medium to large system. Bear in mind, these things are built by teams, and one product or service might actually have hundreds of microservices behind supporting it. Any single one of those could go wrong in a myriad of ways. Even Rain Man would have trouble keeping up with that.

Here's the thing, no process in the world prevents bugs.

Well, that's just patently wrong. A good suite of automated tests supported with good manual QA will prevent bugs. It won't stop everything, but it's far better than not testing.

It's ok to have some kind of "dev" environment to maybe experiment with but ask yourself why cant just test these things locally in the first place.

Some things just can't be easily tested locally, and some things shouldn't be tested by the developer who wrote them. Having testing environments that very closely match production is vital for proper continuous delivery.

While you still have some form of argument for deploying late in the day and just before the weekend, this only works for

  1. projects that are sufficiently small and where it's easier to understand the whole system, or where the change is so small (fixing a typo in a sentence, etc) that there is no way it could affect anything else
  2. projects that you don't care about too much, and don't mind if something is released in a broken state.

Anything else means that you care enough about the project that you don't want to release bugs that could have been caught with a few hours more testing, or that you really aren't 100% sure about the scope of your changes. That latter is ok; as a developer you should be confident that you're not causing side-effects with your changes, but sometimes there can be no guarantee.


A standard code release into production is more like a scheduled operation

My point is for most teams we dont need this overhead, in fact the additional overhead of process and delayed feedback loops makes it even more likely your system to be problematic.

I think it's unreasonable to expect any single dev to understand 100% of a medium to large system.

I agree, but for a given story a developer should have 100%(ish) knowledge of the surface area of what they're changing. Remember agile advocates for small stories so I dont think we're asking too much here. In addition, everything else should be tested so there is very low risk in that respect.

Well, that's just patently wrong.

I think you may have misinterpreted. What I am trying to say is no matter what you do, you will still probably encounter bugs; even with automated tests, manual checking etc.

Re your other points, this approach is successfully used on large systems. Go to any devops-themed conference and they emphasise that this, along with the best practices i described (monitoring, observability, testing, small releases, etc) is the way forward. Re "production like staging environments" I recently went to a conference where the talk had a lot about how the industry is kidding itself if it thinks it can be "production" like in non prod; particulary with distributed systems and the unpredictability of user behaviour. Our time is much better served optimissing for MTTR (mean time to recovery)

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