Re: reverse proxy, disable compression to/from backend, DEFLATE to client

matthias platzer <mplatzer@xxxxxxxx> · Sun, 24 Feb 2008 02:23:45 +0100

Nick Kew schrieb:

On Sun, 24 Feb 2008 00:38:08 +0100

My Apache 2.2.3 does reverse proxy to an internal backend 

(application)server which does Content-Encoding:gzip (=compression)

on most of the content he delivers, by default. The Proxy* directives
are inside a virtual host.

Can you not configure the backend not to send you compressed?

No, can't do...

But I'd like the proxy to do all the compression work,

a) because mod_security cannot handle encoded content(in the response 

from backend),

You can of course decompress on the proxy if necessary, for the
benefit of content filters (such as mod_security).

Yes I thought of that, but it would be somewhat more redundant, the 

backend would have to compress -> proxy decompresses and inspects 

content -> compresses again ...

b) it would be redundant to compress the already compressed content.

So to talk to the backend uncompressed, I strip the Accept-Encoding
with "Request-Header unset Accept-Encoding" from the client request.
Now the backend sends its responses without compression. But they go
to the client uncompressed too, of course.

Yep.

What would I have to do to let the proxy compress the response to the 

client (again)? Simply setting the SetOutputFilter DEFLATE is not

enough. Also I would have to deal with clients not supporting
compression on the proxy myself, instead of letting the backend do
the work.

You can use force-gzip to override the absence of Accept-Encoding.
Use mod_rewrite to set it conditionally, before stripping the real
Accept-Encoding header.

Couldn't I set a EnvVariable if the client wishes compression, then 

strip the Accept-Encoding header, (request goes to backend without 

Accept-Encoding), and then apply a DEFLATE filter on the response to the 

client conditionally, depending on the before set variable? Or like 

compress everything coming from the backend, depending on the initial 

(clients) Accept-Encoding header?

Or maybe I am overestimating the "httpd.conf" potential and there is no 

way to distinguish the response coming from the backend and the response 

going to the client, same applying to the request?

Thanks a lot,
matthias

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