Varnish 4.0.0 technology preview 1 released

Tollef Fog Heen tfheen at
Thu Dec 5 09:08:56 CET 2013

Hot on the heels of Varnish 3.0.5, it is my pleasure to announce the
release of Varnish 4.0.0 technology preview 1.  There are too many
changes to fully enumerate them here, but a small sample is:

 - Full streaming support, including asynchronous backend fetches.    
   This enables Varnish to serve stale objects while it is fetching or   
   revalidating objects from the backend.

 - If-Modified-Since and If-None-Match support to the backend.

 - Directors are now VMODs and are runtime loadable.

 - A complete overhaul of the libvarnishapi and corresponding tools,
   leading to performance and correctness improvements.

 - A more fully-fledged filtering language for querying the Varnish

Please note the VCL syntax has changed and requires upgrading from
previous versions.

Known issues and limitations:
 - varnishhist and varnishtop are known to not work correctly.
 - the documentation is not properly updated yet.  In particular, there
   is not yet any upgrade checklist.

You can download the new release from or replace
varnish-3.0 with varnish-4.0 in the regular installation instructions.

As this release is a technology preview, it is not recommended for
production systems.  Feedback on varnish-dev at and
#varnish-hacking on is most  welcome.

Tollef Fog Heen, on behalf of the Varnish team

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