Still needs testing and verification afterward. Now each instance will have ten chances to break each year instead of one.
Which is likely to be better - first, something that breaks once every couple of years will likely be put up with because it's not worth putting in the effort of fixing. Except now that tribal knowledge is having to be passed on because no one can be bothered to fix it.
If it breaks every other time every few weeks, then there's much more incentive to fix it properly so it quits breaking so often. And something that breaks every few months is more likely to be passed onto the next guy because it's more recent information than something that only happens once every couple of years.
I've worked for companies where changing the TLS certificate on their main public facing websites was a whole process wrapped up in change control.
Probably somebody broke it in the past. I've seen that happen too.
It likely happened because it's a process that doesn't happen often, so all the tricks you learned this time around are forgotten the next time it happens. When a certificate expires yearly, someone has to remember what they did last year in order to renew it all. And likely things broke because they forgot some things.
Once that knowledge gets put into scripts, if in a few months you discover the script overlooked something, you fix the script and make life simple. The script becomes the working memory and if something breaks, the script can be run through manually to ensure every piece is updated.
Also, there's a chance if something breaks, it'll get caught all that much quicker - someone moves a file somewhere and it's forgotten about a year later. Here it's only a month and a half and chances are someone remembers "Oh, we moved that a month ago!".
This ^
And the more complicated the more you want things to be fully automated. Manual enterprise deploys have about an 80% fail rate while automated deploys have a far less than 1% fail rate.
as for "you need to test your site after deploying a new certificate" If it is important enough to be paying someone to work on it, it should be monitored 24x7 anyways.
The biggest problem with the automated certificates is that the tooling around them is so good you have people who set them up and are in charge of them for years and never even figured out what a certificate is so that they have no clue where to start if something breaks. Then again, I frequently delete a computer instead of fixing it. So, maybe it isn't as big of an issue that I'm thinking it is.
