Rails behind multiple proxies

I submitted a patch to fix a problem I have experienced when multiple
proxies are in between the rails process and the browser.


This problem has come up because I have a few rails application on an
intranet where I have to use proxies to provide access to some
clients. I have done little work with this sort of thing before so I
was hoping to get more input from someone on this list.

When multiple proxies have serviced a request the
HTTP_X_FORWARDED_HOST environment variable is created and looks like

HTTP_X_FORWARDED_HOST = “www.firsthost.org, www.secondhost.org

In this case the browser requested a url from www.firsthost.org, which
then forwarded this request to www.secondhost.org which then forwarded
this to the rails application (perhaps hosted via webrick or

When ActionController::redirect_to is called in this scenario an error
occurs because it attempts to redirect to “http://www.firsthost.org,
www.secondhost.org/whatever/url” which is invalid. This happens
because when the hostname is requested by redirect_to it receives back
the whole HTTP_X_FORWARDED_HOST balue. If the browser had requested
the url directly from www.secondhost.org HTTP_X_FORWARDED_HOST would
equal “www.secondhost.org” and this error does not occur.

The patch returns only the first host name if there is a comma
delimited chain. In the example above this results redirects now go
to “http://www.firsthost.org/whatever/url”, and this works in my
setup. Now I am now wondering if I should have made it redirect to the
last hostname in the HTTP_X_FORWARDED_HOST instead. In some setups url
rewriting may be done on www.firsthost.org and it may not be expecting
urls to be redirected with its own host name.

In my environment I am using Apache’s “ProxyPass” and

I am pretty sure now that I should return the last host in the chain,
but I would appreciate some feed back from anyone who may have
experience with this.

Thank you - Gaetano

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