Varnish, The Good, The

Awesome, and the

Downright Crazy By Mike Willbanks

Software Engineering Manager

CaringBridge

MinneBar April 7, 2012

2

•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

Housekeeping…

3

• 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!

Agenda

What the… is Varnish? Official Statement

What the hell it means

Graphs, oh my!

5

“Varnish is a web application accelerator. You install it in

front of your web application and it will speed it up

significantly.”

Official Statement

6

•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

What The Hell? Tell me!

7

•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!

A General Use Case

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The Graph - AWS

0

10000

20000

30000

40000

50000

60000

70000

80000

Small X-Large Small Varnish

Requests

Requests

0

50

100

150

200

250

300

350

400

450

500

Small X-Large Small Varnish

Time

Time

0

100

200

300

400

500

600

700

Small X-Large Small Varnish

Req/s

Req/s

0

2

4

6

8

10

12

14

Small X-Large Small Varnish

Peak Load

Peak Load

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

Comments 19,442 failed reqs

The Good – Listen Up! Installment

Documentation

Finding Existing VCL’s

11

•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

Installment

12

•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.

Documentation

13

•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

Existing VCL’s – The truly lazy…

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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;

}

}

Wordpress = Bad Slashdot Bad!!!

The Awesome – Going Places VCL

Directors

A Few Examples

16

Mind ****

17

•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.

VCL – Varnish Configuration Language

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• 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

• vcl_fini – all requests have exited VCL, cleanup of VMOD’s

VCL - Subroutines

19

• Always Available

now – epoch time

• Backend Declarations

.host – hostname / IP

.port – port number

• Request Processing

client – ip & identity

server – ip & port

req – request information

VCL - Variables

• Backend Req Prepartion

bereq – backend request

• Retrieved Backend Request

beresp – backend response

• Cached Object

obj – Cached object, can only

change .ttl

• Response Preparation

resp – http stuff

20

• 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

VCL - Functions

21

• 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.”

Directors

22

•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

Directors – The Types

23

•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

Director - Probing

24

Example VCL Configuration

The Crazy ESI – Edge-Side Includes

Purging

VMOD

26

•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

ESI – Edge Side Includes

27

ESI – By Diagram

28

• 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

Using ESI

29

<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>

ESI – By Example

30

•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!

Purging – Beer anyone?

31

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

Purging Examples

32

•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.

Sexy Purging

33

•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!

Embedding C in VCL – you must be crazy

34

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

VCL - Embedded C for syslog – uber sexy

35

•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

VMOD – Varnish Modules / Extensions

36

•The VMOD std is shipped with varnish; it provides some

useful commands

toupper

tolower

set_up_tos

Random

Log

VMOD - std

syslog

fileread

duration

integer

collect

Varnish Command Line Apps varnish varnishadm varnishhist

varnishlog varnishncsa varnishreplay

varnishsizes varnishstat varnishtest

varnishtop

38

•What is varnish doing right now?

•How do I debug what is happening?

varnishtop

What is Varnish doing…

39

•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

Logging

40

•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.

Cache Warmup

41

•How to see your cache hit ratios…

varnishstat

•Want to parse them from XML?

varnishstat –x

Cache Hit Ratios? No Problem

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