varnish cache http 301 302 header location redirects

Question

I'm trying to set up an in-the-middle varnish server to allow a Rails app on xyz.com to work on several other domain names.

What happens is that from time to time the Rails app outputs some 301/302 redirects and apparently varnish does not change these headers, so visitors get redirected to the original site (which is behind the public-facing varnish server), so... error.

Is there a way to configure this rewrite on the varnish side of things?

under vcl_fetch I tried the following:

if ( (beresp.status == 301) || (beresp.status == 302) ) {
    set req.url = regsub(req.url,".*",regsuball(regsub(beresp.http.Location,"^http://[^/]+(.*)","\1"),"[+]","%2520"));
    return(restart);

But maybe I don't understand how this works exactly? Any help will be much appreciated

Answer 1

After fighting with your regex an thinking of the use case... I think you would probably can do a much straightforward thing, such as rewrite the location and cache the object corrected (and leave redirection to client browser).

On vcl_fetch:

# ...
if ( beresp.status == 301
  || beresp.status == 302
) {
  # Check if we're redirecting to a different site
  if ( ! beresp.http.Location ~ req.http.host ) {
    # Rewrite HTTP Location header to cache it and pass redirection to client
    set beresp.http.Location = regsub(
                                 beresp.http.Location,
                                 "^http://[^/]+/",
                                 "http://" + req.http.host + "/"
                               );
  }
}
# ...

---

If you still prefer to restart the request on a different url inside Varnish, I'll try (again on vcl_fetch):

# ...
if ( beresp.status == 301
  || beresp.status == 302
) {
  # Add a header so you can debug cleanly on varnishlog
  set req.http.X-Redirected-Orig = beresp.http.Location;
  # Rewrite request host
  set req.http.host = regsub(
                        regsub(
                          beresp.http.Location,
                          "^http://",
                          "",
                        ),
                        "^([^/]+)/.*$",
                        "\1"
                      );
  # Rewrite request url
  set req.url = regsub(
                  beresp.http.Location,
                  "^http://[^/]+/(.*)$",
                  "/\1",
                );
  # Add a header so you can debug cleanly on varnishlog
  set req.http.X-Redirected-To = "http://" + req.http.host + req.url;
  return (restart);
}
# ...

PS: Excuse me for the regsub indentations, but I think it's much more readable with it.