caching the uncacheable: leveraging your cdn to cache dynamic content
Post on 30-May-2015
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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…
Dynamic Content Caching Problems
• Serving stale pages – Lack of good invalida+on framework
Dynamic Content Caching Problems
• Serving stale pages – Lack of good invalida+on framework
• 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
Dynamic Content, Tradi=onally
CDN Node CDN Node
Client
Origin
Lots of TCP Tweaks
Dynamic Content, Tradi=onally
• 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
WordPress: Before
CDN Node
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
WordPress: AWer
CDN Node PURGE
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://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
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
http://collector.site.com/beacon.img?a=1&b=2&c=3
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
http://collector.site.com/beacon.img?a=1&b=2&c=3
AWer
CDN Node
Origin
HTTP/1.1 204 No ContentDate: Sat, 21 Jun 2014 23:21:12 GMTServer: Awesome ServerContent-Length: 0
http://collector.site.com/beacon.img?a=1&b=2&c=3
AWer
CDN Node
Origin
Syslog / S3 / FTP/etc
http://collector.site.com/beacon.img?a=1&b=2&c=3
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!
hooman@fastly.com
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