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Rewrite the varnish cookbook article
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dbu committed Dec 19, 2014
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Expand Up @@ -7,27 +7,102 @@ How to Use Varnish to Speed up my Website
Because Symfony's cache uses the standard HTTP cache headers, the
:ref:`symfony-gateway-cache` can easily be replaced with any other reverse
proxy. `Varnish`_ is a powerful, open-source, HTTP accelerator capable of serving
cached content quickly and including support for :ref:`Edge Side Includes <edge-side-includes>`.
cached content fast and including support for :ref:`Edge Side Includes <edge-side-includes>`.

Trusting Reverse Proxies
------------------------
.. index::
single: Varnish; configuration

Make Symfony Trust the Reverse Proxy
------------------------------------

For ESI to work correctly and for the :ref:`X-FORWARDED <varnish-x-forwarded-headers>`
headers to be used, you need to configure Varnish as a
:doc:`trusted proxy </cookbook/request/load_balancer_reverse_proxy>`.

.. index::
single: Varnish; configuration
.. _varnish-x-forwarded-headers:

Routing and X-FORWARDED Headers
-------------------------------

To ensure that the Symfony Router generates URLs correctly with Varnish,
a ``X-Forwarded-Port`` header must be present for Symfony to use the
correct port number.

This port depends on your setup. Lets say that external connections come in
on the default HTTP port 80. For HTTPS connections, there is another proxy
(as Varnish does not do HTTPS itself) on the default HTTPS port 443 that
handles the SSL termination and forwards the requests as HTTP requests to
Varnish with a ``X-Forwarded-Proto`` header. In this case, you need to add
the following configuration snippet:

.. code-block:: varnish4
sub vcl_recv {
if (req.http.X-Forwarded-Proto == "https" ) {
set req.http.X-Forwarded-Port = "443";
} else {
set req.http.X-Forwarded-Port = "80";
}
}
.. note::

Remember to configure :ref:`framework.trusted_proxies <reference-framework-trusted-proxies>`
in the Symfony configuration so that Varnish is seen as a trusted proxy
and the ``X-Forwarded-*`` headers are used.

Varnish automatically forwards the IP as ``X-Forwarded-For`` and leaves
the ``X-Forwarded-Proto`` header in the request. If you do not configure
Varnish as trusted proxy, Symfony will see all requests as coming through
insecure HTTP connections from the Varnish host instead of the real client.

Configuration
-------------
If the ``X-Forwarded-Port`` header is not set correctly, Symfony will append
the port where the PHP application is running when generating absolute URLs,
e.g. ``http://example.com:8080/my/path``.

As seen previously, Symfony is smart enough to detect whether it talks to a
reverse proxy that understands ESI or not. It works out of the box when you
use the Symfony reverse proxy, but you need a special configuration to make
it work with Varnish. Thankfully, Symfony relies on yet another standard
written by Akamai (`Edge Architecture`_), so the configuration tips in this
chapter can be useful even if you don't use Symfony.
Ensure Consistent Caching Behaviour
-----------------------------------

Varnish uses the cache headers sent by your application to determine how
to cache content. However, versions prior to Varnish 4 did not respect
``Cache-Control: no-cache``. To ensure consistent behaviour, use the following
configuration if you are still using Varnish 3:

.. configuration-block::

.. code-block:: varnish3
sub vcl_fetch {
/* By default, Varnish3 ignores Cache-Control: no-cache and private
https://www.varnish-cache.org/docs/3.0/tutorial/increasing_your_hitrate.html#cache-control
*/
if (beresp.http.Cache-Control ~ "no-cache" ||
beresp.http.Cache-Control ~ "private"
) {
return (hit_for_pass);
}
}
.. code-block:: varnish2
sub vcl_fetch {
// By default, Varnish2 ignores Pragma: nocache and Cache-Control: no-cache and private
if (beresp.http.Cache-Control ~ "no-cache" ||
beresp.http.Cache-Control ~ "private"
) {
return (hit_for_pass);
}
}
Enable Edge Side Includes (ESI)
-------------------------------

As explained in the :ref:`Edge Side Includes section<edge-side-includes>`,
Symfony detects whether it talks to a reverse proxy that understands ESI or
not. When you use the Symfony reverse proxy, you don't need to do anything.
But to make Varnish instead of Symfony resolve the ESI tags, you need some
configuration in Varnish. Symfony uses the ``Surrogate-Capability`` header
from the `Edge Architecture`_ described by Akamai.

.. note::

Expand Down Expand Up @@ -58,22 +133,12 @@ Symfony adds automatically:

.. code-block:: varnish4
/* (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);
}
}
.. code-block:: varnish3
Expand All @@ -84,14 +149,6 @@ Symfony adds automatically:
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
Expand All @@ -102,13 +159,6 @@ Symfony adds automatically:
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::
Expand All @@ -117,6 +167,12 @@ Symfony adds automatically:
(read `GZIP and Varnish`_). If you're not using Varnish 3.0, put a web
server in front of Varnish to perform the compression.

.. tip::

If you followed the advice about ensuring a consistent caching
behaviour, those vcl functions already exist. Just append the code
to the end of the function, they won't interfere with each other.

.. index::
single: Varnish; Invalidation

Expand All @@ -134,139 +190,8 @@ proxy before it has expired, it adds complexity to your caching setup.
invalidation by helping you to organize your caching and
invalidation setup.

Varnish can be configured to accept a special HTTP ``PURGE`` method
that will invalidate the cache for a given resource:

.. code-block:: varnish4
/*
Connect to the backend server
on the local machine on port 8080
*/
backend default {
.host = "127.0.0.1";
.port = "8080";
}
sub vcl_recv {
/*
Varnish default behavior doesn't support PURGE.
Match the PURGE request and immediately do a cache lookup,
otherwise Varnish will directly pipe the request to the backend
and bypass the cache
*/
if (req.request == "PURGE") {
return(lookup);
}
}
sub vcl_hit {
// Match PURGE request
if (req.request == "PURGE") {
// Force object expiration for Varnish < 3.0
set obj.ttl = 0s;
// Do an actual purge for Varnish >= 3.0
// purge;
error 200 "Purged";
}
}
sub vcl_miss {
/*
Match the PURGE request and
indicate the request wasn't stored in cache.
*/
if (req.request == "PURGE") {
error 404 "Not purged";
}
}
.. caution::

You must protect the ``PURGE`` HTTP method somehow to avoid random people
purging your cached data. You can do this by setting up an access list:

.. code-block:: varnish4
/*
Connect to the backend server
on the local machine on port 8080
*/
backend default {
.host = "127.0.0.1";
.port = "8080";
}
// ACL's can contain IP's, subnets and hostnames
acl purge {
"localhost";
"192.168.55.0"/24;
}
sub vcl_recv {
// Match PURGE request to avoid cache bypassing
if (req.request == "PURGE") {
// Match client IP to the ACL
if (!client.ip ~ purge) {
// Deny access
error 405 "Not allowed.";
}
// Perform a cache lookup
return(lookup);
}
}
sub vcl_hit {
// Match PURGE request
if (req.request == "PURGE") {
// Force object expiration for Varnish < 3.0
set obj.ttl = 0s;
// Do an actual purge for Varnish >= 3.0
// purge;
error 200 "Purged";
}
}
sub vcl_miss {
// Match PURGE request
if (req.request == "PURGE") {
// Indicate that the object isn't stored in cache
error 404 "Not purged";
}
}
.. _varnish-x-forwarded-headers:

Routing and X-FORWARDED Headers
-------------------------------

To ensure that the Symfony Router generates URLs correctly with Varnish,
proper ```X-Forwarded``` headers must be added so that Symfony is aware of
the original port number of the request. Exactly how this is done depends
on your setup. As a simple example, Varnish and your web server are on the
same machine and that Varnish is listening on one port (e.g. 80) and Apache
on another (e.g. 8080). In this situation, Varnish should add the ``X-Forwarded-Port``
header so that the Symfony application knows that the original port number
is 80 and not 8080.

If this header weren't set properly, Symfony may append ``8080`` when generating
absolute URLs:

.. code-block:: varnish4
sub vcl_recv {
if (req.http.X-Forwarded-Proto == "https" ) {
set req.http.X-Forwarded-Port = "443";
} else {
set req.http.X-Forwarded-Port = "80";
}
}
.. note::

Remember to configure :ref:`framework.trusted_proxies <reference-framework-trusted-proxies>`
in the Symfony configuration so that Varnish is seen as a trusted proxy
and the ``X-Forwarded-`` headers are used.
The documentation of the `FOSHttpCacheBundle`_ explains how to configure
Varnish and other reverse proxies for cache invalidation.

.. _`Varnish`: https://www.varnish-cache.org
.. _`Edge Architecture`: http://www.w3.org/TR/edge-arch
Expand Down

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