This document provides a summary of Mike Willbanks' presentation on Varnish. The presentation covered an introduction to Varnish including what it is and how it works, the benefits ("The Good"), more advanced features ("The Awesome"), and some complex capabilities ("The Crazy"). It also discussed using the Varnish command line applications and left time for questions.
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Varnish, The Good, The Awesome, and the Downright Crazy
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
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
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
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
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
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