The document provides a comprehensive guide on HTTP caching using Varnish, including installation, configuration, and common pitfalls. It covers topics such as cache control headers, cache validation with ETags, and cache invalidation techniques such as purging and banning. The document also emphasizes the importance of caching strategies for performance improvements, particularly for dynamic content and authenticated responses.

1. HTTP caching
with Varnish
DPC, June 27th 2015
David Buchmann & David de Boer

3. This thing called Varnish

4. # apt-get install varnish
Edit /etc/default/varnish
Replace port 6081 with 80
# service varnish restart

5. Webserver on port 8080
# service apache2 restart

7. What could possibly go
wrong?

8. Nothing gets cached
Too much gets cached
Editors see no changes
Caches get mixed up

9. Let’s take a step back

11. HTTP is simple
GET /path
HTTP/1.1 200 OK
Content-Type: text/html
...

12. Default behaviour
Only GET and HEAD are cached
Cache for 2 minutes
Requests with Cookie/Authorization are not cached
Responses with Set-Cookie are not cached

13. Cache control headers
Cache-Control: s-maxage=3600, max-age=900
Expires: Sat, 27 June 2015 09:58:00 GMT

14. Cache control headers
Set them in your app, not in Varnish
Cache-Control: s-maxage=3600, max-age=900
Expires: Sat, 27 June 2015 09:58:00 GMT

15. Do not cache
Cache-Control: s-maxage=0, private, no-cache

16. Cache validation

17. ETag
Unique resource fingerprint
Client sends ETag
Still the same? 304 Not-Modified
Prefer ETag over Last-Modified

18. curl -o /dev/null -sD - http://fos.lo/path

19. curl -o /dev/null -sD - http://fos.lo/path
HTTP/1.1 200 OK
Date: Fri, 22 Jun 2015 19:23:02 GMT
Cache-Control: s-maxage=30
Vary: Accept-Encoding
Content-Type: application/json
Age: 23
ETag: 4423466221248

21. Plain PHP
header('Cache-Control: s-maxage=600, max-age=60');
header('Etag: ' . sha1($data));

22. Plain PHP
Do this before any output
is sent to the client
header('Cache-Control: s-maxage=600, max-age=60');
header('Etag: ' . sha1($data));

23. Symfony
// DefaultController::indexAction
$response = $this->render('::index.html.twig');
$response->setSharedMaxAge(600);
$response->setMaxAge(60);
$response->setEtag(sha1($response->getContent()));
return $response;

24. Symfony
Add above or annotation to every action
// DefaultController::indexAction
$response = $this->render('::index.html.twig');
$response->setSharedMaxAge(600);
$response->setMaxAge(60);
$response->setEtag(sha1($response->getContent()));
return $response;

25. FOSHttpCacheBundle
app/config/config.yml:
match:
path: "^/articles"
headers:
cache_control:
s_maxage: 600
max_age: 60
etag: true

26. Overview
VCL
Invalidation
Tagging

29. VCL

30. Cookies
sub vcl_recv {
if (req.http.Authorization || req.http.Cookie) {
return (pass);
}
return (hash);
}

31. Remove cookies

32. Remove cookies
sub vcl_recv {
if (req.http.Cookie) {
if (req.url ~ "^/static") {
unset req.http.Cookie;
}
}
}

33. Remove cookies
Adds to default behaviour
sub vcl_recv {
if (req.http.Cookie) {
if (req.url ~ "^/static") {
unset req.http.Cookie;
}
}
}

34. Invalidation

35. There are only two hard things in computer science:
Cache invalidation
Naming things
Off by one errors

36. Invalidation
Actively remove response from cache
Long TTL
More hits

37. Invalidation
Actively remove response from cache
Long TTL
More hits
Remember: bust your assets!

38. Invalidation flavours
Purge: URL and variants
Refresh: exact request, warm cache
Ban: batch with regular expressions

39. Invalidation flavours
Purge: URL and variants
Ban: batch with regular expressions

40. Purge

41. Configure Varnish
acl invalidators {
"localhost";
}
vcl_recv {
if (req.method == "PURGE") {
if (!client.ip ~ invalidators) {
return (synth(405, "Not allowed"));
}
return (purge);
}
}

42. FOSHttpCache
$cacheInvalidator->invalidatePath('/my/path');
...
$cacheInvalidator->flush();

43. Ban

44. Ban is powerful
Regular expressions
URL
And any request header
Custom Varnish configuration

45. Cache taggingCache tagging

46. Set tags
When comment-1 changes:
BAN request
for X-Cache-Tags
that match on: comment-1(,.+)?
X-Cache-Tags: comment-1, comment-2

47. Invalidate tags
sub vcl_recv {
# ...
ban("obj.http.x-cache-tags ~ " +
req.http.x-cache-tags
);
# ...
}

48. FOSHttpCacheBundle
$tagHandler->addTag(['comment-1', 'comment-2']);
$tagHandler->invalidateTags(['comment-1']);
use FOSHttpCacheBundleConfigurationTag;
class CommentController extends Controller
{
/**
* @Tag({"comments", "'comment-'~id"})
*/
public function commentAction($id)
{

49. Wrap-up

50. Increase your hitsIncrease your hits

51. Remove cookies where possible
Cache authenticated content
Increase TTL
Inspect cache misses:
varnishtop -i BereqURL

52. FOSHttpCache
Well-tested Varnish integration for PHP apps
Provides testing tools
Cache authenticated content by group
Also for Nginx & Symfony HttpCache
Extensive documentation
Symfony bundle
Version 2.0: PSR-7, VCL functions

54. KISS VCL
Application performance
Frontend performance

55. Questions, input, feedback?
Twitter:
@dbu @ddeboer_nl
https://joind.in/14240

56. Varnish 4
Client/backend separation
Simpler VCL
Finally takes Cache-Control seriously

57. User context caching
Cache authenticated responses
Cache for groups of users
Let backend decide on groups

58. ESI
<html>
<body>
Main body.
<esi:include src="/esi-fragment.php" />
</body>
</html>

59. Content-negotation
Need to keep variants apart
Request:
Response:
Accept: application/json
Vary: Accept