named group backreference in LocationMatch is not recognized in ProxyPassMatch

Question

my English is rather poor and it is my first question, so hopefully I do it the right way ;-)

I use Apache HTTPD 2.4.41 (Win64) and I wanted to use following LocationMatch-Rule:

<LocationMatch "^/es/(?<ind>.*)/_search$">
    AllowMethods GET POST       
    
    ProxyPassMatch http://localhost:9200/%{MATCH_IND}/_search
    ProxyPassReverse http://localhost:9200
</LocationMatch>

The rule seems to match, as I receive a response from the backend server (ElasticSearch). The response body shows that something did not work with the named group backreference:

GET /es/archives/_search
{
    "error": "no handler found for uri [/%25%7BMATCH_IND%7D/_search/es/archives/_search] and method [POST]"
}

It seems that the named group backreference has not been recognized and has been passed right through to the backend server without being interpreted.

At least, the original URL has been appended (as stated in the doc). As a workaround I could even leave it like this, but in my opinion, it is not the right way to achieve this.

Any Ideas of the reason why both the named group backreference and the variable seems not be recognized by Apache ? My Apache version (2.4.41) should also be fine as named group backreferences have been introduced in version 2.4.8.

I literally spent hours on Stack Overflow and Google searching for a similar situation, but nothing helped so far.

Hope, someone can help!

Answer 1

It seems that <LocationMatch> documentation is a big vague when it comes to using the matched expression with ProxyPass and ProxyPassMatch. The %{MATCH_*} expressions do not seem to work with them. However it seems that back-references (ie. $1) do work. So you probably want something like:

<LocationMatch "^/es/(?<ind>.*)/_search$">
    AllowMethods GET POST       
    
    ProxyPassMatch http://localhost:9200/$1/_search
    ProxyPassReverse http://localhost:9200
</LocationMatch>

Note that named groups need to be used in the regex, otherwise the back-reference won't be populated.