feature #4280 [Cookbook][Cache] Added config example for Varnish 4.0 …

…(thierrymarianne)

This PR was merged into the 2.3 branch.

Discussion
----------

[Cookbook][Cache] Added config example for Varnish 4.0

| Q             | A
| ------------- | ---
| Doc fix?      | [yes]
| New docs?     | [no]
| Applies to    | [all]
| Fixed tickets | []

After upgrading to `Varnish 4.0`, I've noticed the documentation was not really up-to-date anymore:

 * according to https://www.varnish-cache.org/docs/4.0/whats-new/upgrading.html#req-not-available-in-vcl-backend-response,

  `beresp` is available in `vcl_backend_response`

 * according to https://www.varnish-cache.org/docs/4.0/whats-new/upgrading.html#hit-for-pass-objects-are-created-using-beresp-uncacheable,

   `hit_for_pass` objects are created via `beresp.uncacheable`

Would this addition be enough in order to consider the documentation up-to-date in accordance with `Varnish 4.0` upgrading guidelines?

Commits
-------

f3b7394 Added config example for Varnish 4.0

cookbook/cache/varnish.rst

@@ -54,30 +54,62 @@ Then, optimize Varnish so that it only parses the Response contents when there
 is at least one ESI tag by checking the ``Surrogate-Control`` header that
 Symfony adds automatically:
 
-.. code-block:: text
+.. configuration-block::
 
-    sub vcl_fetch {
-        /*
-        Check for ESI acknowledgement
-        and remove Surrogate-Control header
-        */
-        if (beresp.http.Surrogate-Control ~ "ESI/1.0") {
-            unset beresp.http.Surrogate-Control;
+    .. code-block:: varnish4
 
-            // For Varnish >= 3.0
-            set beresp.do_esi = true;
-            // For Varnish < 3.0
-            // esi;
+         /* (https://www.varnish-cache.org/docs/4.0/whats-new/upgrading.html#req-not-available-in-vcl-backend-response) */
+        sub vcl_backend_response {
+            // Check for ESI acknowledgement and remove Surrogate-Control header
+            if (beresp.http.Surrogate-Control ~ "ESI/1.0") {
+                unset beresp.http.Surrogate-Control;
+                set beresp.do_esi = true;
+            }
+            /* By default Varnish ignores Pragma: nocache
+            (https://www.varnish-cache.org/docs/4.0/users-guide/increasing-your-hitrate.html#cache-control)
+            so in order avoid caching it has to be done explicitly */
+            if (beresp.http.Pragma ~ "no-cache") {
+                // https://www.varnish-cache.org/docs/4.0/whats-new/upgrading.html#hit-for-pass-objects-are-created-using-beresp-uncacheable
+                set beresp.uncacheable = true;
+                set beresp.ttl = 120s;
+                return (deliver);
+            }
         }
-        /* By default Varnish ignores Cache-Control: nocache
-        (https://www.varnish-cache.org/docs/3.0/tutorial/increasing_your_hitrate.html#cache-control),
-        so in order avoid caching it has to be done explicitly */
-        if (beresp.http.Pragma ~ "no-cache" ||
-             beresp.http.Cache-Control ~ "no-cache" ||
-             beresp.http.Cache-Control ~ "private") {
-            return (hit_for_pass);
+
+    .. code-block:: varnish3
+
+        sub vcl_fetch {
+            // Check for ESI acknowledgement and remove Surrogate-Control header
+            if (beresp.http.Surrogate-Control ~ "ESI/1.0") {
+                unset beresp.http.Surrogate-Control;
+                set beresp.do_esi = true;
+            }
+            /* By default Varnish ignores Cache-Control: nocache
+            (https://www.varnish-cache.org/docs/3.0/tutorial/increasing_your_hitrate.html#cache-control),
+            so in order avoid caching it has to be done explicitly */
+            if (beresp.http.Pragma ~ "no-cache" ||
+                beresp.http.Cache-Control ~ "no-cache" ||
+                beresp.http.Cache-Control ~ "private") {
+                return (hit_for_pass);
+            }
+        }
+
+    .. code-block:: varnish2
+
+        sub vcl_fetch {
+            // Check for ESI acknowledgement and remove Surrogate-Control header
+            if (beresp.http.Surrogate-Control ~ "ESI/1.0") {
+                unset beresp.http.Surrogate-Control;
+                esi;
+            }
+            /* By default Varnish ignores Cache-Control: nocache
+            so in order avoid caching it has to be done explicitly */
+            if (beresp.http.Pragma ~ "no-cache" ||
+                beresp.http.Cache-Control ~ "no-cache" ||
+                beresp.http.Cache-Control ~ "private") {
+                return (hit_for_pass);
+            }
         }
-    }
 
 .. caution::