Hello,
Recently, while upgrading, my site starts returning a 500.
This is the first time this has happened, but I would like to know how to prevent it, as an inconclusive page that mostly just says “Oops” isn’t exactly useful to users, and creates downtime.
It has been that way all the time 
Because when it is under upgrading it is situation of error 500.
And that’s why we can do this:
Or am I missing now something?
Yeah, I think you’re missing something.
Before I was able to use my site while it was upgrading. Rebuilding isn’t the case but upgrading my site would stay alive
Am I wrong?
I’ve seen this recently and it worried me. This is not normal. It prompted me to perform an “offline” command line upgrade (which was annoying)
I will keep an eye out for it happening again.
