.htaccess 301 redirect old to new domain, from hosting root to subfolder, working but why? - apache

Question

The scenario: I've moved a WordPress website to a new domain and want to 301 redirect all the pages from the old domain to the new domain. Both sites are on the same hosting account running Apache. The old site is at the root level (public_html), and the new site is in a subfolder (below/inside the root).
I've managed to make this work, but I'd like to learn and understand why it works. So below is a quick overview of my 'journey' and solution, together with three specific questions.
First I tried to do the redirects like this (code added to the root .htaccess file):
# 301 Page Redirects - not working - causes redirect loop
redirect 301 / https://new-domain.com/
redirect 301 /services/ https://new-domain.com/services/
redirect 301 /recipes/ https://new-domain.com/recipes/
But this causes a redirect loop. I'm guessing because the .htaccess file with these rules is at the root level and therefore also affects the subfolders.
Question 1: Is my assumption above about the reason for the redirect loop correct?
Then I tried to be more specific and put this code in the root .htaccess file instead:
# 301 Page Redirects - not working - does nothing at all - not sure why
redirect 301 https://old-domain.com/ https://new-domain.com/
redirect 301 https://old-domain.com/services/ https://new-domain.com/services/
redirect 301 https://old-domain.com/recipes/ https://new-domain.com/recipes/
I was hoping the above code would do the trick, because it's more specific about the old domain. My thinking was that it specifies the old domain exactly and so would circumvent the redirect loop. But instead this code seems to have no effect at all. The redirect loop was gone, but now no redirects were happening anymore at all.
Question 2: Why would the above code not produce any redirects at all?
Then I found this answer and applied the code from that, which works perfectly and creates all the redirects. Plus it's much more elegant than my previous attempts above. This is the code:
# 301 Redirects from old-domain.com to new-domain.com - THIS CODE WORKS - Yay!
RewriteEngine On
RewriteCond %{HTTP_HOST} ^old-domain.com$ [OR]
RewriteCond %{HTTP_HOST} ^www.old-domain.com$
RewriteRule (.*)$ https://new-domain.com/$1 [R=301,L]
Question 3: Why does this code not cause any redirect loops when I place it in the root .htaccess?
I realise I'm copy/pasting code without fully understanding why it works. So I'd love an explanation in simple terms about these behaviours. Thank you.

Answer 1

Answer 1:
From the info that you have provided, I would say no. You did not specify if the new-domain.com website is configured (in apache configuration) with its document root being public_root or public_root/subfolder (judging by the described behaviour I would say it is the former). In that case, when you request https://old-domain.com/anything, the server will (because of the unconditional redirect in your first rule) respond with redirect to https://new-domain.com/anything. Client browser will then request that URL and it will hit the same Apache and same .htaccess, which will again result in the same redirect, causing the loop.
Answer 2:
Redirect syntax:
Redirect [status] [URL-path] URL
The old URL-path is a case-sensitive (%-decoded) path beginning with a
slash.
In your rule, you are specifying [URL-path] as https://old-domain.com/, which is wrong: it can be /, /services/, or /recipes, but not https://old-domain.com/ or https://old-domain.com/services/. The request [URL-path] does not match [URL-path] specified in your rule, so redirect never happens.
Answer 3:
This basically does the same thing as your first rule in Answer 1., with one important difference: the server will respond with redirect only if the hostname in request (or to be more precise, the content of the Host: header in request) is equal to old-domain.com or www.old-domain.com, which will prevent the loop since the second request from the client will use new-domain.com hostname.
Also, from the above, seems like your "new" website in subfolder will never be served: either if old-domain.com or new-domain.com is requested, the site from public_html folder will be shown (and only the hostname in clients browser address bar will change).