Configure haproxy to return a 204 for a certain ACL match

I want to return a HTTP 204 error code if anyone tries to access a particular path on my web server. I could set one of my webservers to return a 204 error and point haproxy to it as a backend. However since no information is being sent, I figured this should be possible to do from haproxy itself. No need to bother my actual web servers.

I tried creating a backend that would generate the 204 error as follows:

frontend ...
    ...
    acl is_always204 path_beg /thisone
    use_backend always204 if is_always204
    ...

backend always204
    errorfile 404 /etc/haproxy-shared/errors/204.http

The 204.http file contains:

HTTP/1.0 204 No Content Cache-Control: no-cache Connection: close Content-Type: image/png

When I start haproxy, I get this error:

parsing [/etc/haproxy/haproxy:51] : status code 404 not handled, error customization will be ignored.

I think I may be going about this the wrong way. Can anyone suggest a way to force haproxy to return a 204 for a given acl match?

Solution 1:

As mentioned in the comments, you cannot specify an errorfile for 404, as HAProxy will never generate a 404. You must use something like 503, which HAProxy does actually emit and has a configurable error file. Your 204 file can be used as is, just substitute 503 for 204 in your config.