caching the uncacheable: leveraging your cdn to cache dynamic content

Caching The Uncacheable:

Leveraging Your CDN to Cache Dynamic

Content

Hooman Behesh+, VP Technology

Dynamic Content Is Really Interes=ng!

What Is Dynamic Content? •  Stuff that’s not sta+c! •  With web traffic, generally the base HTML –  Big deal because it’s blocking –  And some+mes the largest object à longer download

•  Could be other things too –  AJAX calls –  API calls

•  More…

Blocking

Classically, with dynamic content…

Caching

Dynamic Content Caching Problems

•  Serving stale pages – Lack of good invalida+on framework

Caching vs.

Invalida=on

We tried…



•  Real-‐+me visibility – Real-‐+me analy+cs/stats – Real-‐+me logging

CDNs and Dynamic Content

•  Generally, handling dynamic content has been a maRer of transport – Op+mize from-‐origin delivery – “DSA” (Dynamic Site Accelera+on) – Middle mile op+miza+ons – TCP tweaks

Dynamic Content, Tradi=onally

CDN Node

Client

Origin

Some TCP Tweaks


CDN Node CDN Node

Client

Origin

Lots of TCP Tweaks


•  We some+mes do micro caching of HTML –  Short TTL for HTML content – Not full proof

•  Ex: news stories faux-‐pas!

•  ESI (Edge Side Includes) –  Par+al caching – Hard and onerous

Actually…

•  Dynamic content is more cacheable than we think

•  Sta+c for short periods of +me

•  Unpredictable invalida+on –  Standard HTTP caching rules aren’t good enough

A Lot BeMer!

CDN Node CDN Node

Client

Origin

Blocking

So Many Benefits!

•  Performance –  Faster +me to first byte –  Faster start render – Happy users!

•  Offload –  Less work for our servers –  Less bandwidth at origin

What would make it beMer?

Programma=c Invalida=on

•  Invalida+on API •  Granular •  Instantaneous – Big problem with classic CDNs (mul+-‐minute purges)

Power of the Purge!

•  Instant purging: – As a page gets published, a purge command also gets published

–  Instant means: predictable and determinis+c behavior

Power of the Purge!

•  Purge dependencies – Surrogate Keys – Using tags to purge en+re chunks of content at once

More than just Invalida=on…

The Influence of Clouds

•  The CDN is an extension of the app •  No longer a black box •  Real-‐+me integra+on with the app •  Infrastructure as code – Your content => You need control

Control

•  Programmability – Configura+on API –  Invalida+on API –  Instantaneous and real +me – Granular caching

•  Ex: Geo-‐based caching

Control at the Edge

•  Moving app logic to the edge •  VCL – Varnish Configura+on Language – Script-‐like configura+on for func+onality at the edge

Visibility

•  Real +me analy+cs – Network stats – HTTP stats (status codes , etc) –  Caching stats (hits, misses, etc) –  Stats API

•  Logging –  Real +me logs –  Streaming to various log des+na+ons

Example: CMS + Purge

WordPress: Before

CDN Node

WordPress: Before

CDN Node

Cache

WordPress: AWer

CDN Node

WordPress: AWer

CDN Node

HTTP/1.1 200 OKContent-Type: text/htmlContent-Length: 55,666Cache-Control: Long Time, totally!

WordPress: AWer

CDN Node

WordPress: AWer

CDN Node PURGE

WordPress: AWer

CDN Node PURGE

(Has to be instantaneous!)

WordPress: AWer

CDN Node

HTTP/1.1 200 OKContent-Type: text/htmlContent-Length: 55,666Cache-Control: Long Time, totally!

Example: Beacon Termina=on at the Edge

Before

CDN Node

Origin

Log Analysis

http://collector.site.com/beacon.img?a=1&b=2&c=3

Before

CDN Node

Origin

Log Analysis

HTTP/1.1 200 OKPragma: no-cacheExpires: Wed, 19 Apr 2000 11:43:00 GMTCache-Control: no-cache, no-storeLast-Modified: Wed, 21 Jan 2004 19:51:30 GMTContent-Type: image/gifDate: Fri, 20 Jun 2014 12:22:20 GMTServer: ApacheContent-Length: 35


AWer

CDN Node

Origin http://collector.site.com/beacon.img?a=1&b=2&c=3

AWer

CDN Node

Origin

HTTP/1.1 200 OKPragma: no-cacheExpires: Wed, 19 Apr 2000 11:43:00 GMTCache-Control: no-cache, no-storeLast-Modified: Wed, 21 Jan 2004 19:51:30 GMTContent-Type: image/gifDate: Fri, 20 Jun 2014 12:22:20 GMTServer: ApacheContent-Length: 35


AWer

CDN Node

Origin

HTTP/1.1 204 No ContentDate: Sat, 21 Jun 2014 23:21:12 GMTServer: Awesome ServerContent-Length: 0


AWer

CDN Node

Origin

Syslog / S3 / FTP/etc


Example: Edge-‐generated Content

JSON Data Center ID

CDN Node

Origin http://www.site.com/which_datacenter.js

JSON Data Center ID

CDN Node

Origin

{ ‘datacenter’ : ‘SJC’ }

http://www.site.com/which_datacenter.js

VCL Snippet

More Examples

•  Caching with tracking cookies: –  hRp://www.fastly.com/blog/how-‐to-‐cache-‐with-‐tracking-‐cookies

•  API Caching: –  hRp://www.fastly.com/blog/api-‐caching-‐part-‐iii (part 3, with links to previous two parts)

•  Log Streaming: –  hRp://www.fastly.com/blog/+ps-‐for-‐streaming-‐logs

Let’s Sum Up!

Summary

•  Dynamic content can be cached – We need instant purging – We need real-‐+me logs and stats

•  Real-‐+me integra+on of our CDN with our app is cool! –  Extensive/granular API to control the CDN –  Control and visibility at the edge lets us be really crea+ve

•  Never use “Long Time, totally!” in a Cache-Control header!

Thank you!

[email protected]