This document summarizes Mike Willbanks' presentation on Varnish to the MinneBar group on April 7, 2012. The presentation covered an introduction to Varnish including what it is and how it works, the benefits of using Varnish to accelerate websites ("The Good"), more advanced Varnish features like VCL and directors ("The Awesome"), and complex Varnish configurations involving ESI, purging, and embedding C code in VCL ("The Crazy"). It also provided overviews of various Varnish command line applications for monitoring and debugging Varnish like varnishtop, varnishstat, and varnishlog.

1. MinneBar April 7, 2012
Varnish, The Good, The
Awesome, and the
Downright Crazy
By Mike Willbanks
Software Engineering Manager
CaringBridge

2. Housekeeping…
• Talk
 Slides will be online later!
• Me
 Software Engineering Manager at CaringBridge
 MNPHP Organizer
 Open Source Contributor (Zend Framework and various others)
 Where you can find me:
• Twitter: mwillbanks G+: Mike Willbanks
• IRC (freenode): mwillbanks Blog: http://blog.digitalstruct.com
• GitHub: https://github.com/mwillbanks
2

3. Agenda
• What the … is Varnish?
• The Good
 “I don’t want to listen to you but only want to play on my laptop.”
 The quick, easy and uninformed way... You listening over there?
• The Awesome
 VCL’s, Directors and more… now we’re going places.
• The Crazy
 ESI, Purging, VCL C, and VMOD… my head hurts, stop!
• Varnish Command Line Apps
 varnishtop, varnishstat, etc.
• Questions
 Although you can bring them up at anytime!
3

4. What the… is Varnish?
Official Statement
What the hell it means
Graphs, oh my!

5. Official Statement
“Varnish is a web application accelerator. You install it in
front of your web application and it will speed it up
significantly.”
5

6. What The Hell? Tell me!
• Varnish allow you to accelerate your website
 By using memory and keeping in mind cookies, request headers
and more…
• It caches pages so that your web server can RELAX!
 What about my apache, tomcat, uhhh… (mongrel|thin|goliath….)
 Generally caching by TTL + HTTP Headers (cookies too!)
• A load banancer, proxy and more…
 What? …. Yes, it can do that! #winning
6

7. A General Use Case
• CaringBridge Status Server
 We need to get a message to our mobile users!
 The system is down, or we want to be able to communicate a
message to them about some subject… maybe a campaign.
 The apps and mobile site rely on an API
• Trouble in paradise? Few and far in between.
• We want to talk to our users? Of course!
 Let an API talk to a server…
 A story on crashing and burning
 A story on a bad thing making a huge success!
7

8. The Graph - AWS
Req/s Peak Load
700 14
600 12
500 10
400 8
300 Req/s Peak Load
6
200 4
100
2
0
0
Small X-Large Small Varnish
Small X-Large Small Varnish
Time Requests
500 80000
450 70000
400
60000
350
300 50000
250 40000
Time Requests
200 30000
150
20000
100
50 10000
0 0
8 Small X-Large Small Varnish Small X-Large Small Varnish

9. The Raw Data
Small X-Large Small Varnish
Concurrency 10 150 150
Requests 5000 55558 75000
Time 438 347 36
Req/s 11.42 58 585
Peak Load 11.91 8.44 0.35
19,442
Comments failed reqs
9

10. The Good – Listen Up!
Installment
Documentation
Finding Existing VCL’s

11. Installment
• RTM : http://goo.gl/hl4Tt
 Debian: sudo apt-get install varnish
 EPEL: yum install varnish
• only 6.x otherwise you’ll be out of date!
 WOOT Compiling #winning #git
• git clone git://git.varnish-cache.org/varnish-cache
• cd varnish-cache
• sh autogen.sh
• ./configure
• Make && make install
11

12. Documentation
• Reference Manual
 https://www.varnish-cache.org/docs/3.0/reference/index.html
• Tutorial – more like a book version of the reference manual
 https://www.varnish-cache.org/docs/3.0/tutorial/index.html
• Knock yourselves out! There is a ton of documentation
• Yes, this makes happy developers.
 Documentation is very accurate, read carefully.
 Focus heavily on VCL’s, that is generally what you need.
 I’m attempting to show you some of how this works but you will
require the documentation to assist you.
12

13. Existing VCL’s – The truly lazy…
• VCL’s are available for common open source projects
 Hi wordpress and drupal!
• https://www.varnish-cache.org/trac/wiki/VarnishAndWordpress
• https://www.varnish-cache.org/trac/wiki/VarnishAndDrupal
 Examples of all sorts of crazy
• https://www.varnish-cache.org/trac/wiki/VCLExamples
13

14. Wordpress = Bad Slashdot Bad!!!
backend default {
.host = "127.0.0.1“;
.port = "8080";
}
sub vcl_recv {
if (!(req.url ~ "wp-(login|admin)")) {
unset req.http.cookie;
}
}
sub vcl_fetch {
if (!(req.url ~ "wp-(login|admin)")) {
unset beresp.http.set-cookie;
}
}
14

15. The Awesome – Going Places
VCL
Directors
A Few Examples

16. Mind ****
16

17. VCL – Varnish Configuration Language
• VCL State Engine
 Each Request is Processed Separately & Independently
 States are Isolated but are Related
 Return statements exit one state and start another
 VCL defaults are ALWAYS appended below your own VCL
• VCL can be complex, but…
 Two main subroutines; vcl_recv and vcl_fetch
 Common actions: pass, hit_for_pass, lookup, pipe, deliver
 Common variables: req, beresp and obj
 More subroutines, functions and complexity can arise dependent
on condition.
17

18. VCL - Subroutines
• vcl_init – VCL is loaded, no request yet; VMOD initialization
• vcl_recv – Beginning of request, req is in scope
• vcl_pipe – Client & backend data passed unaltered
• vcl_pass – Request goes to backend and not cached
• vcl_hash – call hash_data to add to the hash
• vcl_hit – called on request found in the cache
• vcl_miss – called on request not found in the cache
• vcl_fetch – called on document retrieved from backend
• vcl_deliver – called prior to delivery of cached object
• vcl_error – called on errors
18
• vcl_fini – all requests have exited VCL, cleanup of VMOD’s

19. VCL - Variables
• Always Available • Backend Req Prepartion
 now – epoch time  bereq – backend request
• Backend Declarations • Retrieved Backend Request
 .host – hostname / IP  beresp – backend response
 .port – port number • Cached Object
• Request Processing  obj – Cached object, can only
 client – ip & identity change .ttl
 server – ip & port • Response Preparation
 req – request information  resp – http stuff
19

20. VCL - Functions
• hash_data(string) – adds a string to the hash input.
 Request host and URL is default from the default vcl.
• regsub(string, regex, sub) – substitution on first occurance
 sub can contain numbers 0-n to inject matches from the regex.
• regsuball(string, regex, sub) – substitution on all occurances
• ban(expression) – Ban all objects in cache that match
• ban(regex) – Ban all objects in cache that have a URL match
20

21. Directors
• Directors allow you to talk to the backend servers
• Directors are a glorified reverse proxy
 Allows for certain types of load balancing
 Allows for talking to a cluster
“A director is a logical group of backend servers
clustered together for redundancy. The basic role of
the director is to let Varnish choose a backend server
amongst several so if one is down another can be
used.”
21

22. Directors – The Types
• Random Director – picks a backend by random number
• Client Director – picks a backend by client identity
• Hash Director – picks a backend by URL hash value
• Round-Robin Director – picks a backend in order
• DNS Director – picks a backend by means of DNS
 Random OR Round-Robin
• Fallback – picks the first “healthy” backend
22

23. Director - Probing
• To ensure healthy backends, you need to use probing.
 It really sounds like a colonoscopy for servers.
• Variables
 .url
 .request
 .window
 .threshold
 .intial
 .expected_response
 .interval
 .timeout
23

24. Example VCL Configuration
24

25. The Crazy
ESI – Edge-Side Includes
Purging
VMOD

26. ESI – Edge Side Includes
• ESI is a small markup language much like SSI (server side
includes) to include fragments (or dynamic content for that
matter).
• If don’t think you can use varnish because you have say,
user information displayed on every page; think again!
• Think of it as replacing regions inside of a page as if you
were using XHR (AJAX).
• Three Statements are Implemented
 esi:include – Include a page
 esi:remove – Remove content
 <!-- esi --> - ESI disabled, execute normally
26

27. ESI – By Diagram
27

28. Using ESI
• In vcl_fetch, you must set ESI to be on
 set beresp.do_esi = true;
 By default, ESI will still cache, so add an exclusion if you need it
• if (req.url == “/show_username.php”) {
return (pass);
}
 Varnish refuses to parse content for ESI if it does not look like XML
• This is by default; so check varnishstat and varnishlog
28

29. ESI – By Example
<html>
<head><title>Rock it with ESI</title></head>
<body>
<header>
<esi:include src="/user_header.php" />
<!-- Don't do this as you'd lose the advantage of varnish -->
<!--esi
<?php include 'user_header.php'; ?>
-->
</header>
<section id="main"></section
<footer></footer>
</body>
</html>
29

30. Purging – Beer anyone?
• Sometimes, you just need to purge.
 Don’t drink too much tonight, ok?
• If you do… find a DD or a cab.
• The various ways of purging
 varnishadm – command line utility
• It’s the ole finger in the back of the throat
 Sockets (port 6082) – everyone likes a good socket wrench
• Sure, Ipecac is likely overkill.
 HTTP – now that is the sexiness
• See, now we’re not forcing the point!
30

31. Purging Examples
varnishadm -T 127.0.0.1:6082 purge req.url == "/foo/bar“
telnet localhost 6082
purge req.url == "/foo/bar
telnet localhost 80
Response:
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
PURGE /foo/bar HTTP/1.0
Host: bacon.org
31

32. Sexy Purging
• Distributed Purging… now that’s a punch line!
 Use a message queue (or gearman job server)
 Have a worker that knows about the varnish servers
 Submit the request to clear the cache in the asynchronously or
synchronously depending on your use case.
• Have enough workers to make this effective at purging the cache
quickly.
32

33. Embedding C in VCL – you must be crazy
• Before getting into VMOD; did you know you can embed C
into the VCL for varnish?
• Want to do something crazy fast or leverage a C library for
pre or post processing?
• I know… you’re thinking that’s useless..
 On to the example; and a good one from the Varnish WIKI!
33

34. VCL - Embedded C for syslog – uber sexy
C{
#include <syslog.h>
}C
sub vcl_something {
C{
syslog(LOG_INFO, "Something happened at VCL line XX.");
}C
}
# Example with using varnish variables
C{
syslog(LOG_ERR, "Spurious response from backend: xid %s request %s %s
"%s" %d "%s" "%s"", VRT_r_req_xid(sp), VRT_r_req_request(sp),
VRT_GetHdr(sp, HDR_REQ, "005host:"), VRT_r_req_url(sp),
VRT_r_obj_status(sp), VRT_r_obj_response(sp), VRT_GetHdr(sp, HDR_OBJ,
"011Location:"));
}C
34

35. VMOD – Varnish Modules / Extensions
• Taking VCL embedded C to the next level
• Allows you to extend varnish and create new functions
• Now, if you are writing modules for varnish you have a
specialty use case!
 Go read up on it!
 https://www.varnish-cache.org/docs/trunk/reference/vmod.html
35

36. VMOD - std
• The VMOD std is shipped with varnish; it provides some
useful commands
 toupper  syslog
 tolower  fileread
 set_up_tos  duration
 Random  integer
 Log  collect
36

37. Varnish Command Line Apps
varnish varnishadm varnishhist
varnishlog varnishncsa varnishreplay
varnishsizes varnishstat varnishtest
varnishtop

38. What is Varnish doing…
• What is varnish doing right now?
• How do I debug what is happening?
 varnishtop
38

39. Logging
• Many times people want to log the requests to a file
 By default Varnish only stores these in shared memory.
 Apache Style Logs
• varnishncsa –D –a –w log.txt
39

40. Cache Warmup
• Need to warm up your cache before putting a sever in the
queue or load test an environment?
 varnishreplay –r log.txt
• Replaying logs can allow you to do this. This is great for
when you are going to be deploying code to check for
performance issues.
40

41. Cache Hit Ratios? No Problem
• How to see your cache hit ratios…
 varnishstat
• Want to parse them from XML?
 varnishstat –x
41

42. Questions?
These slides will be posted to SlideShare & SpeakerDeck.
Slideshare: http://www.slideshare.net/mwillbanks
SpeakerDeck: http://speakerdeck.com/u/mwillbanks
Twitter: mwillbanks
G+: Mike Willbanks
IRC (freenode): mwillbanks
Blog: http://blog.digitalstruct.com
GitHub: https://github.com/mwillbanks