That is wild. I have been maintaining servers with many services and upgrading never broke anything, funnily enough: on Arch Linux. All the systems where an upgrade broke something were Ubuntu-based ones. So perhaps the issue was not so much about the services themselves, but the underlying Linux distribution and its presumably shitty package manager? I do not know the specifics so I cannot say, but in my case it was always the issue. Since then I do not touch any distribution that is not pacman-based, in fact, I use Arch Linux exclusively, with OpenBSD here and there.
i used "broken" generously. it basically means that for example for multiple php based services, we had to upgrade them all at once, which lead to a large downtime until everything was up and running again. services in containers meant that we could deal with them one at a time and dramatically reduce the downtime and complexity of the upgrade process.
Would there still have been a problem if you were able to install multiple php versions side-by-side? HPC systems also have to manage multiple combinations of toolchains and environments and they typically use Modules[1] for that.
probably not, but it wasn't just php, and also one of the goals was the ability to scale up. and so having each service in its own container meant that we could move them to different machines and add more machines as needed.
