Accept-Encoding and Vary header issue

Igor Minar iiminar at
Wed Jul 21 18:40:14 CEST 2010

Hi there,

I came across this interesting Varnish 2.1.2 behavior that I think is a bug.


sub vcl_recv {
  call normalize_accept_encoding;

sub vcl_fetch {
  if (beresp.http.Vary ~ ".+") {
    set beresp.http.Vary = "Accept-Encoding"; #the app doesn't do this

If I make an "uncompressed request" (curl -O -v
I prime the cache with uncompressed variant of bar resource

on subsequent uncompressed request, I get cache hit and the resource
is returned.

if I then (before TTL) make a "compressed request" (curl -O -v -H
I'd expect to get cache miss and prime the cache with compressed
variant of bar resource,
but instead I get cache hit, and the uncompressed variant is returned.

once TTL is achieved, if I make a compressed request, varnish
correctly fetches the compressed variant of the resources, primes the
cache with it and returns it.

if I subsequently (before TTL) make an uncompressed request, varnish
correctly fetches the uncompressed variant from the backend and caches

everything is good until the TTL for the compressed variant is
reached, from that moment on varnish starts serving uncompressed
variant for both compressed and uncompressed requests, until the TTL
for the uncompressed variant is reached.

My current workaround is to control variants manually via vcl_hash:

sub vcl_hash {
  # consider different Accept-Encoding requests (normalized) as new variants
  set req.hash += req.http.Accept-Encoding;

but I don't think that this should be necessary. Am I doing something
wrong or is this a bug?


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