Redirect Loop, Faraway so Close - apache

Question

Basically I need to let through requests to a specific path:
https://domainfoo.com/my-app?param1=ABC&paramY=123
Anything else, let's say,
https://domainfoo.com/aboutus
I need it redirected to
https://moodomain.io/aboutus
I need this last part to be generic.
So Far I have this two rules:
To address the first requirement:
RewriteCond %{HTTP_HOST} ^domainfoo.com$
RewriteCond %{REQUEST_URI} ^/my\-app
RewriteRule ^(my\-app)$ https://domainfoo.com/$1 [L,R=301]
Then as a second rule (if first rule is matched (the L) should redirect and stop right? The thing is apparently it doesn't and then goes into the second rule:
RewriteCond %{HTTP_HOST} ^domainfoo.com$ [OR]
RewriteCond %{HTTP_HOST} ^www.domainfoo.com$
RewriteCond %{REQUEST_URI} !^/my\-app$
RewriteRule (.*)$ https://moodomain.io/$1 [R=301,L]
But I have been dealing for hours with a looped redirect.
Ideas?

Answer 1

You first rule codes the rewriting loop, since you implemented an external redirection where none is required at all. Here is a simplified version:
RewriteEngine on
RewriteCond %{HTTP_HOST} ^domainfoo\.com$
RewriteRule ^/?my-app$ - [END]
RewriteCond %{HTTP_HOST} ^domainfoo\.com$
RewriteRule ^/?(.*)$ https://moodomain.io/$1 [R=301]
It is a good idea to start out with a 302 temporary redirection and only change that to a 301 permanent redirection later, once you are certain everything is correctly set up. That prevents caching issues while trying things out...
In case you receive an internal server error (http status 500) using the rule above then chances are that you operate a very old version of the apache http server. You will see a definite hint to an unsupported [END] flag in your http servers error log file in that case. You can either try to upgrade or use the older [L] flag, it probably will work the same in this situation, though that depends a bit on your setup.
This rule will work likewise in the http servers host configuration or inside a dynamic configuration file (".htaccess" file). Obviously the rewriting module needs to be loaded inside the http server and enabled in the http host. In case you use a dynamic configuration file you need to take care that it's interpretation is enabled at all in the host configuration and that it is located in the host's DOCUMENT_ROOT folder.
And a general remark: you should always prefer to place such rules in the http servers host configuration instead of using dynamic configuration files (".htaccess"). Those dynamic configuration files add complexity, are often a cause of unexpected behavior, hard to debug and they really slow down the http server. They are only provided as a last option for situations where you do not have access to the real http servers host configuration (read: really cheap service providers) or for applications insisting on writing their own rules (which is an obvious security nightmare).
And if you need to redirect clients "back" to the first domain, as you later stated in the comments to the question, then add an explicit redirection for that:
RewriteCond %{HTTP_HOST} !^domainfoo\.com$
RewriteRule ^/?my-app$ https://domainfoo.com/my-app [R=301]