For web sites with frequent content changes, like news portals, an optimal cache strategy is crucial for serving millions of page views. To just cache every page statically is usually not an option as editors want to see the changes immediately. With the new version of eZ Publish CMS, which is based on Symfony PHP framework, content caching is based on HTTP Cache. This enables much tighter integration with reverse proxies like Varnish and better control of cached pages. Also, Symfony provides ESI capabilities for controlling reverse proxy cache even on block level so invalidating a whole page is not expensive.

1. The power of ESI and
HTTP Cache for
performant page delivery
Ivo Lukač @ ZgPHP Conference 2014, Zagreb

2. www.netgenlabs.com
Warning!
• Not so much code in the slides
• This is more about using right tools for
the job and integrating those tools

3. www.netgenlabs.com
Netgen
• Web technology company, established 2002
• Focused on middle and big size web projects based on eZ
Publish CMS and Symfony
• eZ Business partner from 2007
• Working for eZ Systems on core eZ ver 5 stuff from 2012
• Very active in the community
• Organised 3rd in a row eZ/PHP Summer Camp, more than
90 people from across EU this September in Rovinj

4. www.netgenlabs.com

5. www.netgenlabs.com
The problem
• Middle and big size web sites need to be cached
on various levels as much as possible
• But the specific cache needs to be invalidated
when there is some change in the content
• So simple “cache everything with TTL in days“ is
not an option if there are frequent content
changes on sites that are also cross linked a lot
(e.g. News, Media, Portals, etc)

6. www.netgenlabs.com
News, Media, etc

7. www.netgenlabs.com
Agenda
• How to cache content pages and invalidate when necessary
• How to cache parts of content pages and invalidate when
necessary
Focus on optimal cache strategy:
invalidate only when there is a change in
content
* We are not covering caching of static assets like css, javascript and
images. These are usually cached with long TTL and versioned with
hash in the url

8. www.netgenlabs.com
Part 1
• How to cache content pages and invalidate
when necessary:
- use a powerful CMS
- with a good framework
- and a fast reverse proxy
- which all support W3C standards :)

9. www.netgenlabs.com
eZ Publish CMS
• Powerful enterprise open source CMS
• Developed and supported by eZ Systems, Norway
• Symfony full stack from eZ version 5.0
• Latest versions: 5.3 EE and 2014.07 CE

10. Content caching in eZ
• eZ Publish has an integrated content caching
system that figures out when to invalidate what
page cache: Smart View Cache
• In version 4 cache was stored to files locally
• In version 5 it uses HTTP Cache implementation
from Symfony to integrate reverse proxies for
content caching
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11. Smart View Cache rules
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example
[folder]
DependentClassIdentifier[]=frontpage
ClearCacheMethod[]=object
ClearCacheMethod[]=relating
[article]
DependentClassIdentifier[]=folder
DependentClassIdentifier[]=frontpage
ClearCacheMethod[]=object
ClearCacheMethod[]=relating

12. www.netgenlabs.com
Symfony
• Powerful and modern PHP framework
• Separated in many components
• Big community
• Excellent documentation
• Supported by Sensio Labs
• Latest version: 2.5.5

13. www.netgenlabs.com
HTTP Cache
• Part of RFC 2616 (HTTP/1.1)
• 2 models of cache handling:
• Expiration: “Cache-Control”, “Expires”
• Validation: “ETag", “Last-modified”
(not implemented with eZ 5 yet as it doesn’t
behave very well in multiuser scenario)

14. www.netgenlabs.com
Expiration with
Cache-Control
• setting headers to public instead of private
to cache pages in reverse proxy (private is
default in Symfony)
• setting max-age header (or specifically s-maxage)
to some bigger number (days or
even more)

15. www.netgenlabs.com
Cache miss
credits to http://tomayko.com/writings/things-caches-do

16. www.netgenlabs.com
Cache hit
credits to http://tomayko.com/writings/things-caches-do

17. In Symfony?
use SymfonyComponentHttpFoundationResponse;
$response = new Response();
// mark the response as either public or private
$response->setPublic();
$response->setPrivate();
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// set the private or shared max age
$response->setMaxAge(600);
$response->setSharedMaxAge(600);

18. Finally some code!
www.netgenlabs.com

19. www.netgenlabs.com
But what about
invalidation?
• as the Etag is not implemented yet a different
mechanism is used to invalidate cache
• custom header X-Location-Id: 123 is set to mark the
page with location id 123
• eZ content caching mechanism calls HTTP
command PURGE against the reverse proxy when
its necessary to invalidate a specific cache

20. www.netgenlabs.com
How eZ does it?
# stock ViewController::viewLocation()
$response->setPublic();
if ( $this->getParameter( 'content.ttl_cache' ) === true )
{
$response->setSharedMaxAge( $this->getParameter( 'content.default_ttl' ));
}
if ( $request->headers->has( 'X-User-Hash' ) )
{
$response->setVary( 'X-User-Hash' );
}
$response->headers->set( 'X-Location-Id', $locationId );

21. Reverse proxy becomes
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very important
• Reverse proxy AKA web accelerator or
gateway cache
• preferred with Symfony and eZ Publish:
Varnish Cache

22. www.netgenlabs.com
Varnish Cache
• HTTP reverse proxy (web accelerator)
• Performant and configurable
• Supports most important parts of ESI
• Supported by Varnish Software
• Latest version: 4.0

23. Varnish Cache setup
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• we need to support PURGE call
sub vcl_recv {
if (req.request == "PURGE") { return(lookup); }
}
sub vcl_hit {
if (req.request == "PURGE") {
set obj.ttl = 0s;
error 200 "Purged";
}
}
sub vcl_miss {
if (req.request == "PURGE") { error 404 "Not purged”; }
}

24. www.netgenlabs.com
Part 2
• How to cache parts of content pages and
invalidate when necessary:
- use a powerful CMS
- with a good framework
- and a fast reverse proxy
- which all support ESI :)

25. Block caching in eZ
• Repeatable parts of a page need special
attention (header, menus, footer, sidebars, etc)
• In eZ version 4 cache blocks were stored to files
locally
• In eZ version 5 it uses the same HTTP Cache
principles but with ESI powered fragments
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26. Fragments in Symfony
• Enable sub requests to be callable via URI
• Trust only certain IPs (reverse proxies) to call it
• Could be used directly from web clients (from javascript with
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hinclude.js) but then the call must be signed
# app/config/config.yml
framework:
esi: { enabled: true }
fragments: { path: /_fragment }
trusted_proxies: [127.0.0.1, 10.0.0.0/8]

27. Edge Side Includes
• Markup protocol for proxies to cache partial pages
• Specified by Akamai
• Implemented by many proxies, including Varnish
• The most simple implementation:
<esi:include src=“http://foo.bar/1.html"/>
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28. Include ESI block
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• render sub request as ESI in Symfony (will
generate ESI markup if stated in the request):
{{ render_esi( controller(
'aController:someAction',
{ 'foo': 'bar' }
))
}}

29. Cache control on block
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level
• as each block is a sub request we can set different
headers (private or public, ttl, etc.)
• this can be per block type (from settings) or even per
block (parameter set by editor)
• when it makes sense X-Location-Id header is set
automatically so the cache can be invalidated

30. Varnish Cache setup
• when Varnish request a page from the web server it needs to tell
that it wants ESI markup instead of rendered HTML
www.netgenlabs.com
sub vcl_recv {
// Add a header to announce ESI support.
set req.http.Surrogate-Capability = "abc=ESI/1.0";
}

31. www.netgenlabs.com
Result?
• common blocks have long TTL and get rarely
executed on backend
• they are mostly just embedded from cache when
the reverse proxy builds the page with ESI tags
• possible different cache strategies for different
pages, zones and blocks across the whole site

32. www.netgenlabs.com
Caution
• A rule of thumb is not to have more than 10 sub
requests in one page render
• As there might be lot of blocks on the page we
create zones of blocks that are rendered as sub
request with a small TTL (that way we spread the
sub requests over more page renderings)

33. Achieved scenario
• When an editor creates some new content
(article) in a news section (folder), CMS will
automatically purge the cache of the folder and
the latest news block on the frontage so that
the new article shows up instantly on both
pages without touching other cache
www.netgenlabs.com

34. www.netgenlabs.com

35. Questions now or later
ivo@netgen.hr
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