Varnish 4.0.1 and IMS

[Geoff Simmons]

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On 8/29/14 10:05 PM, Madhusudan Ramanna wrote:
> 
> I thought Varnish 4.0.1 has support for IMS.  But looks like
> varnish is not sending the IMS header to the backend.  Or I'm
> missing something.
> 
> *   << Request  >> 32820 -   ReqHeader      User-Agent: curl/7.24.0
> (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8y zlib/1.2.5 
> -   ReqHeader      Host: <<host>> -   ReqHeader      Accept: */* -
> ReqHeader      If-Modified-Since: Sat, 05 Oct 2013 10:19:56 GMT -
> ReqHeader      X-Forwarded-For: <<ip>>
> 
> -   BereqHeader    User-Agent: curl/7.24.0
> (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8y zlib/1.2.5 
> -   BereqHeader    Host: <<host>> -   BereqHeader    Accept: */* -
> BereqHeader    X-Forwarded-For: <<ip>> -   BereqHeader
> Accept-Encoding: gzip -   BereqHeader    X-Varnish: 65570

You have IMS in the client request, which Varnish has handled for some
time. If Varnish finds a cache hit, and the object in cache has a
Last-Modified header, then Varnish will respond accordingly (no
backend request necessary). That's not new in version 4.

What's new is that Varnish will add IMS to backend requests to refresh
objects from its cache with expired TTL, for those objects that have a
Last-Modified header, and if the keep timer has not expired.

What you're missing is that you apparently expected the IMS header in
the client request to be forwarded to the backend request. But Varnish
won't do that for a cache miss -- the response might be cacheable, in
which case we'll want the whole thing. Once you have the response in
cache, then it can be refreshed via IMS.


Best,
Geoff
- -- 
UPLEX Systemoptimierung
Scheffelstraße 32
22301 Hamburg
http://uplex.de/
Mob: +49-176-63690917
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