An introduction to varnish cache for PHP developers.

1. Mike Willbanks | Barnes & Noble
Varnish Cache

2. Housekeeping…
• Talk
– Slides will be posted after the talk.
• Me
– Sr. Web Architect Manager at NOOK
Developer
– Prior MNPHP Organizer
– Open Source Contributor
– Where you can find me:
• Twitter: mwillbanks G+: Mike Willbanks
• IRC (freenode): mwillbanks Blog:
http://blog.digitalstruct.com
• GitHub: https://github.com/mwillbanks

3. Agenda
• Varnish?
• The Good : Getting Started
• The Awesome : General Usage
• The Crazy : Advanced Usage
• Gotchas

4. Official Statement
What it does
General use case
WHAT IS VARNISH?

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.”

9. You can cache…
Both dynamic and static files and contents.

10. A Scenario
• System Status Server
– Mobile apps check current status.
– If the system is down do we communicate?
– If there are problems do we communicate?
– The apps and mobile site rely on an API
• Trouble in paradise? Few and far in between.

11. 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
Small X-Large Small Varnish Small X-Large Small Varnish

12. 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
failed
Comments
requests

13. Load Balancer
HTTP Server Cluster
Database
Traditional LAMP Stack

14. Load Balancer
Yes
Varnish Cache Cache Hit
No
HTTP Server Cluster
Database
LAMP + Varnish
* Varnish can act as a load balancer.

15. Installation
General Information
Default VCL
THE GOOD – JUMP START

16. Installation
rpm --nosignature -i http://repo.varnish-cache.org/redhat/varnish-3.0/el5/
noarch/varnish-release-3.0-1.noarch.rpm
yum install varnish
curl http://repo.varnish-cache.org/debian/GPG-key.txt | sudo apt-key add -
echo "deb http://repo.varnish-cache.org/ubuntu/ lucid varnish-3.0" | sudo
tee -a /etc/apt/sources.list
sudo apt-get update
sudo apt-get install varnish
git clone git://git.varnish-cache.org/varnish-cache
cd varnish-cache
sh autogen.sh
./configure
make && make install

17. Varnish Daemon
• varnishd
– -a address[:port] listen for client
– -b address[:port] backend requests
– -T address[:port] administration http
– -s type[,options] storage type (malloc, file,
persistence)
– -P /path/to/file PID file
– Many others; these are generally the most
important. Generally the defaults will do with
just modification of the default VCL (more on it
later).

18. General Configuration
• varnishd -a :80
-T localhost:6082
-f /path/to/default.vcl
-s malloc,512mb
• Web server to listen on port 8080

19. Setup a backend!
backend default {
.host = “127.0.0.1”
.port = “8080”
}

20. So what’s actually caching?
• Any requests containing
– GET / HEAD
– TTL > 0
• What cause it to miss?
– Cookies
– Authentication Headers
– Vary “*”
– Cache-control: private

21. Request
req.
vcl_recv
req. req. req.
bereq. bereq. req. bereq.
vcl_pass vcl_miss vcl_hash vcl_pipe
req.
req.
bereq.
vcl_fetch vcl_hit obj.
beresp.
resp.
vcl_deliver
Response

22. HTTP Caching
• RFC 2616 HTTP/1.1 Headers
– Expiration
• Cache-Control
• Expires
– Validation
• Last Modified
• If-Modified-Since
• ETag
• If-None-Match

23. TTL Priority
• VCL
– beresp.ttl
• Headers
– Cache-control: s-max-age
– Cache-control: max-age
– Expires
– Validation

24. Use Wordpress?
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;
}
}

25. VCL
Directors
Verifying VCL
THE AWESOME – VCL,
DIRECTORS AND MORE

26. 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.

27. Request
req.
vcl_recv
req. req. req.
bereq. bereq. req. bereq.
vcl_pass vcl_miss vcl_hash vcl_pipe
req.
req.
bereq.
vcl_fetch vcl_hit obj.
beresp.
resp.
vcl_deliver
Response

28. VCL - Process
VCL Process Description
vcl_init Startup routine (VCL loaded, VMOD init)
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 Creates cache hash, call hash_data for custom hashes
vcl_hit Called when hash found in cache
vcl_miss Called when hash not found in cache
vcl_fetch Called to fetch data from backend
vcl_deliver Called prior to delivery of response (excluding pipe)
vcl_error Called when an error occurs
vcl_fini Shutdown routine (VCL unload, VMOD cleanup)

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

30. VCL - Functions
VCL Function Description
hash_data(string) Adds a string to the hash input
regsub(string, regex, sub) Substitution on first occurrence
regsuball(string, regex, sub) Substitution on all occurrences
ban(expression) Ban all items that match expression
ban(regex) Ban all items that match regular expression

31. Request
req.
vcl_recv
req. req. req.
bereq. bereq. req. bereq.
vcl_pass vcl_miss vcl_hash vcl_pipe
req.
req.
bereq.
vcl_fetch vcl_hit obj.
beresp.
resp.
vcl_deliver
Walking through the noteworthy items.
DEFAULT VCL Response

33. vcl_recv
• Received Request
• Only GET & HEAD by default
– Safest way to cache!
• Will use HTTP cache headers.
• Cookies or Authentication Headers will
bust out of the cache.

35. vcl_hash
• Hash is what we look for in the cache.
• Default is URL + Host
– Server IP used if host header was not set;
in a load balanced environment ensure you
set this header!

37. vcl_fetch
• Fetch retrieves the response from the
backend.
• No Cache if…
– TTL is not set or not greater than 0.
– Vary headers exist.
– Hit-For-Pass means we will cache a pass
through.

38. Common adjustments to make.
GENERAL ADJUSTMENTS

39. Cache Static Content
No reason that static content should not be cached.

40. Remove GA Cookies
GA cookies will cause a miss; remove them prior to going to the
backend.

41. Allow Purging
Only allow from localhost or trusted server network.

42. Leveraging backend servers
DIRECTORS

43. Directors – The Types
Director Type Description
Random Picks based on random and weight.
Client Picks based on client identity.
Hash Picks based on hash value.
Round Robin Goes in order and starts over
DNS Picks based on incoming DNS host,
random OR round robin.
Fallback Picks the first “healthy” server.

44. Director - Probing
• Backend Probing
• Variables
– .url
– .request
– .window
– .threshold
– .intial
– .expected_response
– .interval
– .timeout

45. Load Balancing
Implementing a simple varnish load balancer.
Varnish does not handle SSL termination.

46. Grace Mode
Request already pending for update; serve grace content.
Backend is unhealthy.
Probes as seen earlier must be implemented.

47. Saint Mode
Backend may be sick for a particular piece of content
Saint mode makes sure that the backend will not request the object
again for a specific period of time.

48. Purging
• The various ways of purging
– varnishadm – command line utility
– Sockets (port 6082)
– HTTP – now that is the sexiness

49. 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
curl –X PURGE http://bacon.org/foo/bar

50. Distributed Purging
• curl multi-request (in php)
• Use a message queue
– Use workers to do the leg work for you
• You will need to store a list of servers “somewhere”

51. 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
– This will run as a daemon to log all of your
requests on a separate thread.

52. Logging
Apache style logging using: varnishncsa -O -a -w log.txt

53. You likely want to ensure that your cache is:
1. Working Properly
2. Caching Effectively
VERIFY YOUR VCL

54. What is Varnish doing…
Varnishtop will show you real time information on your system.
• Use -i to filter on specific tags.
• Use -x to exclude specific tags.

55. Checking Statistics…
Varnishstat will give you statistics you need to know how you’re
doing.

56. ESI – Edge-Side Includes
Varnish Administration
VMOD
THE CRAZY

57. 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).
• Think of it as replacing regions inside of a
page as if you were using XHR (AJAX) but
single threaded.
• Three Statements can be utilized.
– esi:include – Include a page
– esi:remove – Remove content
– <!-- esi --> - ESI disabled, execute normally

58. <esi:include
src="header.php" />
V B
a a
r c
n k
i e
Page Content s n
h d
ESI Diagram
Varnish detects ESI, requests from backend OR checks cached
state.

59. Using ESI
• In vcl_fetch, you must set ESI to be on
– set beresp.do_esi = true;
– Varnish refuses to parse content for ESI if
it does not look like XML
• This is by default; so check varnishstat and
varnishlog to ensure that it is functioning like
normal.

60. ESI Usage
<html>
<head><title>Rock it with ESI</title></head>
<body>
<header>
<esi:include src=”header.php" />
</header>
<section id="main">...</section>
<footer></footer>
</body>
</html>

61. Embedding C in VCL
• 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!

62. Embedded C for syslog
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

63. Varnish Modules / Extensions
• Taking VCL embedded C to the next
level
• Allows you to extend varnish and create
new functions
• You could link to libraries to provide
additional functionality

64. VMOD - std
• toupper • syslog
• tolower • fileread
• set_up_tos • duration
• random • integer
• log • collect

65. Management Console
Cache Warm up
ADMINISTERING VARNISH

66. Management Console
• varnishadm –T localhost:6062
– vcl.list – see all loaded configuration
– vcl.load – load new configuration
– vcl.use – select configuration to use
– vcl.discard – remove configuration

67. Cache Warmup
• Need to warm up your cache before
putting a sever in the queue or load test
an environment?
– varnishreplay –r log.txt

68. Having Keep-Alive off
No SSL Termination
No persistent cache
ESI multiple fragments
Cookies*
GOTCHAS

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