This document discusses using Varnish as a reverse proxy and HTTP accelerator. It begins with an overview of reverse proxies and caching, then describes how Varnish handles cache hits and misses. Specific techniques covered include using HTTP headers like Cache-Control and surrogate keys to manage caching and invalidations. The document also shows how to configure Varnish using Varnish Configuration Language (VCL) and integrate it with Rails applications and services like image processing.

1. HTTP Acceleration with Varnish

2. HotelTonight
Mobile-first
10k Hotel Partners
17 Countries
~9M Downloads

3. I WANNA
GO FAST

4. Overview
Reverse Proxies
HTTP Headers
Cache Invalidation
Varnish Configuration Language

5. Reverse proxy
In computer networks, a reverse proxy is a type of
proxy server that retrieves resources on behalf of a
client from one or more servers.

6. Request / Response Cycle
Client
Reverse
Proxy
Origin Server
www.hward.com
hward.herokuapp.com
(CNAME)
(or IP Address)

7. Web application accelerator.

8. Reverse proxy
w/ caching
Web application accelerator.

9. Cache Miss
Client
Varnish
Cache
Origin Server

10. Cache Hit
Client
Varnish
Cache
Origin Server

11. Initial use of Varnish
Started with a small portion of our traffic.
33% Hits, 1% Misses, 66% Passes

12. The best traffic is traffic that never
hits our servers.

13. Continue to migrate endpoints
to Varnish
Removed 10 EC2 XLarge Instances!

14. Varnish as a service.
•
Dashboards and Stats
•
RESTful API
•
Killer support team (thanks Peter and Austin)
•
Similar pricing to Cloudfront

15. Fastly
Point of Presence (PoP)
N. America
Australia
Europe
N. America
PoPs
Australia
PoPs
Europe
PoPs
Origin Server

16. Simulated traffic w/ Loader.io

17. 73k req sec
1ms avg. response

18. HTTP Headers
HTTP header fields are components of the message
header of requests and responses in the Hypertext
Transfer Protocol.

19. Rails Default Behavior
Opt-in to Edge Cache
Client
Varnish
Origin Server
Cache
$
<
<
<
curl -v https://launchpad.37signals.com/basecamp -o /dev/null
HTTP/1.1 200 OK
Cache-Control: max-age=0, private, must-revalidate
Set-Cookie: _launchpad_session=[DIGEST]; path=/; HttpOnly; secure

20. Edge-Cache Headers
Only cache publicly accessible pages.
Cache-Control Header:
public, max-age or s-maxage > 0, and remove
any cookies from the response.
$ curl -v http://www.example.com -o /dev/null
< HTTP/1.1 200 OK
< Cache-Control: max-age=30, public

21. max-age
vs.
s-maxage

22. max-age
used on both client and proxy for content expiration
s-maxage
used only by proxy for content expiration

23. Cache-Control Headers for
Static Assets
$
<
<
<
<
<
curl -v http://www.hward.com/assets/blog-f764a70dc0ca4e7bf340d1.css
HTTP/1.1 200 OK
Cache-Control: public, max-age=31557600
Content-Type: text/css
Status: 200 OK
Via: 1.1 varnish

24. Cache-Control Headers for
Dynamic Content
$
<
<
<
<
<
curl -v http://www.hward.com
HTTP/1.1 200 OK
Cache-Control: public, no-cache, s-maxage=31557600
Content-Type: text/css
Status: 200 OK
Via: 1.1 varnish

25. Rails Controllers

26. Verify cache is warming up
$
<
<
<
<
!
$
<
<
<
<
curl -v http://www.hward.com -o /dev/null
HTTP/1.1 200 OK
X-Served-By: cache-sv61-SJC3
X-Cache: MISS
X-Cache-Hits: 0
curl -v http://www.hward.com -o /dev/null
HTTP/1.1 200 OK
X-Served-By: cache-sv61-SJC3
X-Cache: HIT
X-Cache-Hits: 1

27. Cache Invalidation
•
Time based expiration
•
Resource based expiration
•
Surrogate-Keys

28. 1000 Requests / Minute
Cache TTL
Hit Ratio
Origin Requests / Minute
5 sec
98.00%
20
30 sec
99.80%
2
1 min
99.90%
1
5 min
99.997%
<1

29. 50,000
1000 Requests / Minute
Cache TTL
Hit Ratio
Origin Requests / Minute
5 sec
99.96%
20
30 sec
99.996%
2
1 min
99.998%
1
5 min
99.999%
<1

30. PURGE Requests
Invalidate cache with PURGE request to URL.
$ curl -v -X PURGE http://www.hward.com
> PURGE / HTTP/1.1
< HTTP/1.1 200 OK
< Status: 200 OK
< Via: 1.1 varnish
{"status": "ok", "id": "68-1392243590-232248"}
Note: In Production make sure to whitelist IP’s that can Purge.

31. Surrogate-Keys (Fastly Specific)
http://www.fastly.com/blog/surrogate-keys-part-1
posts/1
comments/1
comments/2

32. Many-to-Many Relationship
Between Keys and Pages
posts/1

34. Purging a Surrogate-Key
posts/1

35. Varnish Configuration Language
(VCL)

36. Imagery Service
Dynamically resized images for all devices.
640x260
640x900
412x
412

37. Initially used Magickly Gem
Client
Varnish
Magickly
Gem
S3 Bucket
example.com/image.jpg?resize=500x500#

38. Transition to ImgIX
Client
Varnish
S3 Bucket
example.com/image.jpg?w=500&h=500&crop=fit

39. Re-write URL for backwards
compatibility with VCL

40. Additional Topics
•
Vary Headers
•
Logging
•
Shielding
•
Grace-period for stale cache

41. Questions?
Harlow Ward
@futuresanta
harlow@hoteltonight.com
$25 Promo Code: HARLOW