Cache Optimization with Akamai

Blake Crosby Julian Dunn Media Operations and Technology CBC/Radio-Canada Cache Optimization & Origin Infrastructure Reduction Using Akamai Site Delivery

About CBC
Canada’s public broadcaster offering services in both English, French, and eight other aboriginal languages.
Our services are offered in the following formats:
Radio (FM, AM, Satellite, and Short wave)
Television (digital cable and OTA. Both standard and high definitions)
Online (cbc.ca and radio-canada.ca)

Agenda
Why optimize?
Requirements
Lessons learned at CBC
How to optimize
Current performance

Why Use Akamai Site Delivery?
Reduce origin footprint and costs
Capital expenses and replacement
Operating (systems admin, power, maintenance)
Scalability
Akamai provides CBC with “unlimited” capacity and scaling
Speed
Last mile acceleration by being as close as possible to end users

Conflicting Requirements
Business: “Make the content as fresh as possible.”
IT: “Keep the configuration as simple as possible.”
Finance: “Keep our costs as low as possible.”

The Optimization Spectrum
Two ends of the spectrum
Tune to the Nth degree
High origin offload
Content will not appear very fresh due to long TTLs
Complicated tuning
Low risk to origin due to spikes in traffic.
Don’t tune at all
Lower origin offload
Content appears very fresh
No tuning parameters
High risk to origin due to spikes in traffic

Before Tuning, Understand Your Business and Content
CBC is primarily a news site.
Spiky traffic patterns
Content has to be fresh
Content almost never changes after the first 24-48 hours
Content is not targeted to individuals
No sessions
Personalization is done via Javascript
Deliberate architectural choices:
Site is mostly static by design
Server Side Includes technology used heavily
Executing application layer code for identical requests is wasteful
The lessons we teach here are domain specific.
Understand Your Content!

Ultimate Priorities
Origin stability
Content freshness
Performance
Cost

Overall Lessons Learned
Don’t ignore the architecture of your origin.
Keep caching rules simple
Is the default “good enough”?
Tune at the origin first rather than at the edge
Reduces propagation time for TTLs during emergencies.
Understand and categorize content before tuning.
Understand what “TTL” actually means
Leads to us heavily leveraging If-Modified-Since

How We Did It
Almost no tuning
Default blanket site TTL of 20s for all objects except HTML; 120s for text/html
Most objects have no explicit TTL beyond this
Heavy leveraging of If-Modified-Since
After TTL expiry, Akamai will issue GET with an If-Modified-Since header
Origin returns 304 Not Modified if the object hasn’t been changed
304s account for >85% of our origin hits

Typical Origin Response Codes

How We Did It
Control TTLs at origin.
Fine grain control of object TTLs
Instant results, no need to wait for Akamai configuration to deploy.
Ability to adjust TTLs on the fly during special events or emergency situations.
Using Apache and mod_expires: <Location "/includes"> ExpiresByType "text/css" "access plus 1 hour" ExpiresByType "application/x-javascript" "access plus 1 hour" ExpiresByType "image/gif" "access plus 1 hour" </Location>

How We Did It
Categorize your content.
We’ve categorized our content into three buckets: frequently changing, moderately changing, and never changing.
TTLs applied site wide to objects that fall into these categories.
Some Examples:
Frequently Changing:
XML Data Files (live feeds)
Moderately Changing
HTML Files (news stories)
XML Data Files (weather feeds)
Images
Never Changing
Common site elements (navigation)
Javascript/CSS
favicon.ico

How We Did It
Enable Last Mile Acceleration.
Using LMA allows Akamai to deliver content as compressed objects to the end user from the edge.
We also use mod_deflate to compress our content and deliver it to Akamai.

How We Did It
Use All Available Cache Headers!
Cache-Control
The TTL is located in the “max-age” parameter
“ public” should also be specified to ensure that other caches cache the content.
Expires
The date the object expires
Last-Modified
The last-modified header is sent with all objects with the exception of dynamic content and HTML (explained later).
E-Tag (be careful!)
E-Tags are a “hash” of the files’ inode and last modified time.

How We Did It Content-Type: text/css Last-Modified: Mon, 07 Jun 2010 15:59:39 GMT Etag: "8a14b9cd-84a-c29470c0" Cache-Control: public, max-age=1557 Expires: Tue, 06 Jul 2010 21:38:51 GMT Date: Tue, 06 Jul 2010 21:12:54 GMT X-Cache: TCP_IMS_HIT from a72-246-43-6 (AkamaiGHost/5.9.4-6329478) (-) X-Cache-Key: /L/1849/9617/0s/www.cbc.ca/includes/objects/program-switcher/switcher.css X-True-Cache-Key: /L/www.cbc.ca/includes/objects/program-switcher/switcher.css X-Akamai-Session-Info: name=PARENT_SETTING; value=TD X-Serial: 1849 Connection: keep-alive Vary: Accept-Encoding X-Check-Cacheable: YES

Some Gotchas and Annoyances
There are some situations which make controlling caching difficult. Here is how we’ve dealt with them.
Server Side Includes
Apache cannot calculate the last modified timestamp for files with server side includes (roughly 99% of all html pages on cbc.ca).
We’ve applied a blanket 2 min TTL on all files with the “text/html” content type
Geolocation
Server side customization of content will not work as it will be cached for all users.
We’ve mitigated this by having all customization occur on the client side. If a cookie does not exist, then the browser makes a POST request (which isn’t cached) to the origin to set a cookie which contains the users location.

Tools To Help You
Use the Akamai Portal (Akamai Edge Control)
The “origin OK volume per URL” report is handy in determining which objects are being fetched from the origin.
404s are not cached. Check the “top URLs, by number of errors” to help you track down broken links.
Firefox Plugins
Firebug allows you to view HTTP request and response headers to troubleshoot caching problems.
Akamai Headers is a plugin that will allow you to view Akamai specific information such as the cache key and which Ghost server responded to your request. Available from Akamai Edge Control.
Other Resources
Web Caching By Dune Wessels (O’Reilly and Associates)

Examples (Quebec Earthquake: June 23, 2010)

Examples (FIFA World Cup: June 11, 2010)

The Outcome
Almost no tunables used
Meet the requirements using <25 lines of tunables
No edge tunables in our Akamai metadata config
Capital Expenditure avoidance
Ran with six origin webservers from 2003-2010
Today we run nine origin webservers at about 40% CPU utilization

Questions Thank You!

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Cache Optimization with Akamai

by blakecrosby on Jun 13, 2011

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Cache Optimization with Akamai — Presentation Transcript