This document provides an overview of Varnish, an open source caching reverse proxy that can accelerate web applications. It discusses what Varnish is, how it works, basic and advanced configuration options like backends, VCL, caching strategies, and Edge Side Includes. Installation and usage is demonstrated on common operating systems. The presentation aims to help attendees understand when and how to use Varnish to improve application performance.

1. Accelerate your app with a
layer of Varnish

2. Who?
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Ex-pat Englishman, now living in Southern
Ontario.
Web developer for 5 years, mostly PHP.
(Almost) Senior Software Engineer at
TribeHR.
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Co-organiser of Guelph PHP User Group.
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Ex-professional musician.

3. Varnish can do incredible
things for your app...

4. What is Varnish?
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Open source caching reverse proxy or
HTTP accelerator.
Mature software:
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Current version: 3.0.5
Varnish 4 currently in tech preview.
Used by 5% (500) of the top 10,000
sites on the internet.

5. Varnish basics
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Listens on a port (normally 80).
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When a request arrives:
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If content is already in cache it is served
directly.
If not Varnish forwards the request to a
'backend' server, delivering the content
when it is received.
Only caches GET and HEAD requests.

6. Varnish features
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Can cache any kind of content
delivered via HTTP.
Blazingly fast with incredible
performance.
Support for multiple backends and
basic load balancing.

7. Varnish features (cont)
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Configuration through Varnish
Configuration Language (VCL).
Support for Edge Side Includes (ESI).
Behaviour can be extended through
Varnish Mods (VMODs).
Includes tools to monitor and tune
(varnishtop, varnishlog, varnishhist,
varnishstat, etc).

8. Show us the demo!
https://github.com/JCook21/VarnishDemo

9. Apache results

10. Varnish Results

11. Is Varnish always the right
tool?
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What kind of content are you serving?
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Cookies.
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SSL.
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Varnish is like a layer of... varnish.
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Do you really need Varnish?

12. Getting started with Varnish

13. Setting cache times
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Two possible methods
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HTTP cache headers
Directly in VCL
Prefer HTTP cache headers wherever
possible.

14. Supported OS's
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Fully supported:
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Linux
FreeBSD
'Try not to break':
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OpenBSD
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NetBSD
OS X
Needs a 64 bit OS ideally.

15. Installing Varnish
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Use system package manager.
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For Debian, Ubuntu and RedHat/CentOS
Varnish software maintains repositories
with up to date versions.
To obtain up to date version to install
on non-core supported platforms
compile from source.
More info at the Varnish website.

16. Basic configuration
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Ships with an excellent, 'sane' default
VCL configuration.
To begin using Varnish:
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Configure runtime options
(/etc/default/varnish).
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Add one or more backends to VCL file
(/etc/varnish/default.vcl).

17. Adding VCL backends
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Must add at least one backend in VCL.
If more than one, first will be the
default.
Backends can be grouped into
'directors' to apply load balancing.

18. Sample backend definition
backend default {
.host = "127.0.0.1";
.port = "8080";
}

19. Advanced configuration

20. Introduction to VCL
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Provides a window into Varnish's state
during the request/response cycle.
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Not a full programming language.
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C/Perl-like syntax.
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Compiled into a C shared object at
runtime and loaded into Varnish.

21. VCL Subroutines
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Dispatched at different times in the
request/response cycle.
Each routine has default code:
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Varnish appends this to the end of any code
you add.
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Can be short-circuited by using the return
keyword. Be careful!
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Allowed return values documentation.
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You can also define your own.

22. VCL Subroutines (cont)
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vcl_init
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vcl_miss
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vcl_recv
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vcl_fetch
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vcl_pipe
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vcl_deliver
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vcl_pass
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vcl_error
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vcl_hash
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vcl_fini
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vcl_hit

23. VCL Processing Cycle

24. VCL Functions
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Functions Varnish makes available to you:
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regsub(str, regex, sub)
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regsuball(str, regex, sub)
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ban(ban expression)
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ban_url(regex) (Deprecated)
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purge()
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hash_data(str)
return()
Also have set and unset keywords to manipulate
variables and call to dispatch your own subroutines.

25. vcl_recv
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Called once the OS kernel has given
the complete request to Varnish.
Typical uses:
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Set the backend to use.
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Amend the request.
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Add extra information to the request.
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Force a bypass of cache lookups (pass or
pipe).

26. vcl_fetch
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Called when a response is received
from a backend, before it is considered
for inclusion in the cache.
Typical uses:
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Amend or set a TTL.
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Add or remove HTTP headers.
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Detect errors (more later).
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Turn on ESI processing.

27. Select a backend
backend default {
.host = "192.168.2.1";
.port = "8080";
}
backend bar {
.host = "192.168.2.2";
.port = "8080":
}
sub vcl_recv {
if (req.http.host ~ "bar.com") {
set req.backend = bar;
}
// etc
}

28. Remove cookies
sub vcl_recv {
if (req.url !~ "^/admin/.*") {
unset req.http.cookie;
}
}
sub vcl_fetch {
if (req.url !~ "^/admin/.*") {
unset beresp.http.set-cookie;
}
}

29. Set default TTL
sub vcl_fetch {
if (! beresp.http.cache-control &&
beresp.http.content-type ~ "text/html|
text/xml|application/json") {
set beresp.ttl = 5m;
}
}

30. VMOD's
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Allow you to extend Varnish's features.
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Written in C.
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Community VMOD's at
https://www.varnish-cache.org/vmods
Examples:
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Geo-IP lookup (BBC)
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Query string normalisation
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Memcache

31. Grace mode
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Graced content is an object that has
expired but is kept in cache.
Grace mode is when a graced object is
used.
When this can happen:
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No healthy backends are available.
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Deliver old content while fetching new
content is pending.

32. Configuring grace
sub vcl_recv {
if (req.backend.healthy) {
set req.grace = 30s;
} else {
set req.grace = 1h;
}
}
sub vcl_fetch {
set beresp.grace = 1h;
}

33. Health checks
backend foo {
.host = "192.168.2.1";
.port = "8080";
.max_connections = 10;
.probe = {
.url = "/test";
.interval = 5s;
.timeout = 1s;
.window = 5;
.threshold = 3;
}
}

34. Saint mode
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Allows you to say that a backend is
'sick' for one url.
Varnish will not make further requests
to that backend for the url for the time
specified.
Gives you a chance to detect errors in
responses.

35. Saint mode example
sub vcl_fetch {
if (beresp.status ~ “^5d{2}$”) {
set beresp.saintmode = 10s;
return(restart);
}
}

36. Edge Side Includes
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Allows different content on the same
page to be cached for different times.
Request flow:
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External request returns a page with special
ESI tags in it.
For each ESI tag Varnish issues a sub
request which generates the content.
Both 'master' and sub requests can be
cached.

37. Configuring ESI's
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Done in vcl_fetch:
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set beresp.do_esi = true;
Need to configure app to support
'layouts' and 'components'.
Various frameworks have support for
ESI's.

38. ESI Example
<!DOCTYPE html>
<html>
<head>
<title>ESI example</title>
</head>
<body>
<esi:include src="/route/to/content"/>
</body>
</html>

39. Thanks for listening!
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Varnish docs:
https://www.varnish-cache.org/docs/3.0/tutorial/inde
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Any questions?
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Feel free to contact me:
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@JCook21
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jeremycook0@gmail.com