Integrating multiple CDN providers at Etsy - Velocity Europe (London) 2013

Integrating Multiple CDN Providers
Our experiences at Etsy

@lozzd • @ickymettle

Marcus Barczak

Laurie Denness

Staff Operations Engineers

Beginning of 2010

Today

Background
▪ First started using a single CDN in 2008
▪ Exponential Growth
▪ Start of 2012 began investigation into running

multiple CDNs


Why use a CDN?
▪ Goal: Consistently fast user experience globally
▪ Improve last mile performance by caching content

close to the user
▪ Offload content delivery from origin infrastructure
to the CDN provider


Why use more than one CDN?
▪ Resilience
-

Eliminate single point of failure

▪ Flexibility
-

Balance traffic based on business requirements

▪ Cost
-

Manage provider costs

The Plan

http://www.ﬂickr.com/photos/malloy/195204215

The Plan
1. Establish evaluation criteria
2. Initial configuration and testing
3. Test with production traffic
4. Operationalising


Evaluation Criteria

http://www.ﬂickr.com/photos/49212595@N00/5646403386

Evaluation Criteria
▪ Performance
▪ Configuration
▪ Reporting, Metrics and Logging
▪ Culture


Performance
▪ Baseline Response Times
-

Should be within ±5% of our existing CDN provider’s
response times

▪ Hit Ratios and Origin Offload
-

Provider should achieve equivalent or better origin offload
performance and hit ratios


Configuration
▪ Complexity
-

how complex is the providers configuration system

▪ Self service
-

can you make changes directly or do they require
professional services or other intervention

▪ Latency for changes
-

how quickly do changes take to propagate

Reporting, Metrics and Logging
▪ Resolution
▪ Latency
▪ Delivery
▪ Customisation


Culture
▪ Understand our culture
▪ Postmortems
▪ Access to technical staff
▪ Shared success


Initial
Configuration
and Testing


Clean the house
http://www.ﬂickr.com/photos/mastergeorge/8562623590

Clean the house
▪ Managing caching TTLs from origin
-

CDNs honour the origin cache-control headers!

<LocationMatch ".(gif|jpg|jpeg|png|css|js)$">
Header set Cache-Control "max-age=94670800"
</LocationMatch>


Clean the house
▪ Manage gzip compression from origin
-

Honoured by CDNs

-

Compression from origin to CDN

## mod_deflate compression - see OPS-1537 ##
AddOutputFilterByType DEFLATE text/html text/plain
text/css application/x-javascript [..]


Clean the house
If you can do it at origin,
do it at origin


Mean Time To Curl
http://www.ﬂickr.com/photos/wwarby/3297205226

curl -i -H 'Host: img0.etsystatic.com'
global-ssl.fastly.net/someimage.jpg
HTTP/1.1 200 OK
Server: Apache
Last-Modified: Sat, 09 Nov 2013 23:43:38 GMT
Cache-Control: max-age=94670800
[...]
X-Served-By: cache-lo82-LHR
X-Cache: MISS
X-Cache-Hits: 0

curl -i -H 'Host: img0.etsystatic.com'
global-ssl.fastly.net/someimage.jpg
HTTP/1.1 200 OK
Server: Apache
Last-Modified: Sat, 09 Nov 2013 23:43:38 GMT
Cache-Control: max-age=94670800
[...]
X-Served-By: cache-lo82-LHR
X-Cache: HIT
X-Cache-Hits: 1

Mean Time To Curl = Done
https://www.etsy.com/listing/99871278

Mean Time To Curl
▪ No need to touch existing infrastructure
▪ Smoke test of functionality
▪ 10 minutes from configuration to curl
▪ New providers should be plug and play


Testing In Production
http://www.ﬂickr.com/photos/solarnu/10646426865

Testing with Production Traffic
▪ Images only at first
▪ Good test of caching performance
▪ Easy to test by swapping hostnames
▪ Made even easier with our A/B testing framework


A/B Test Framework
▪ Fine grained control
▪ Enable test for specific users or groups
▪ Percentage of users
▪ All controlled via configuration in code
▪ Rapid and complete rollback


Configure Mappings to CDNs
$server_config["image"] = array(
'akamai' => array(
'img0-ak.etsystatic.com',
'img1-ak.etsystatic.com',
),
'edgecast' => array(
'img0-ec.etsystatic.com',
'img1-ec.etsystatic.com',
),
'fastly' => array(
'img0-f.etsystatic.com',
'img1-f.etsystatic.com',
),
);


Test Controls
$server_config['ab']['cdn'] = array(
'enabled' => 'on',
'weights' => array(
'akamai'
=> 0.0,
'edgecast' => 0.0,
'fastly'
=> 0.0,
'origin'
=> 100.0,
),
'override' => 'cdn_diversity',
);


Metrics and Monitoring

http://www.ﬂickr.com/photos/nicolasﬂeury/6073151084


Even if it doesn’t move, graph it anyway

Simplest approach: Provider’s dashboards


▪ Get more detail by pulling metrics in house
▪ Write script to pull data from API
▪ Create dashboards with data


Testing Plan
1. for c in $cdns; do rampup $c; done;
2. Deliberately slow and steady
3. Watch traffic increase
4. Watch origin offload increase
5. Watch performance


Downsides of this approach
▪ AB testing can’t be used for main site
▪ Exposing your test CNAMEs
▪ Especially if hotlinking is a concern


Downsides of this approach
▪ Exposing your test CNAMEs
▪ Especially if hotlinking is a concern


How do you know it’s broke?
▪ Check the graphs!
▪ Check with your community
▪ Keep support in the loop


Operationalising


Content Partitioning


Etsy’s site partitioning
Dynamic HTML Content
www.etsy.com



Static Assets (js, css, fonts)
site.etsystatic.com


Listing Images, Avatars
imgX.etsystatic.com


Dynamic HTML Content
www.etsy.com
Static Assets (js, css, fonts)
site.etsystatic.com
Listing Images, Avatars
imgX.etsystatic.com


Balancing Traffic in
Production

http://www.ﬂickr.com/photos/wok_design/2499217405

Balancing Traffic Using DNS
▪ Traffic Manager
▪ Extends DNS to dynamically return records based

on rules
▪ Weighted round robin


[2589:~] $ dig +short www.etsy.com
www.etsy.com.edgekey.net.
e2463.b.akamaiedge.net.
23.74.122.37
etsy.com.
cs34.adn.edgecastcdn.net.
38.123.123.123
93.184.219.54
global-ssl.fastly.net.
185.31.19.184


etsy.com.
38.123.123.123
www.etsy.com.edgekey.net.
e2463.b.akamaiedge.net.
23.74.122.37
cs34.adn.edgecastcdn.net.
93.184.219.54
global-ssl.fastly.net.
185.31.19.184


▪ Rule updates typically made via web UI
▪ Can be slow and error prone
▪ Changes need to be applied to all three domains
▪ API available to make changes programmatically


cdncontrol

http://www.ﬂickr.com/photos/foshydog/4441105829

cdncontrol


DNS balancing downsides
▪ Low TTLs for fast convergence
▪ Mo QPS == Mo Money
▪ More DNS lookups for users
▪ Not 100% instant or

deterministic


50% within 1
minute
Long Tail is Loooong


Monitoring in Production

Whoopsie Page
▪ Static HTML delivered for 5xx errors
-

Branding

-

Translated error messages

-

Links to status page


Failure Beacons
1. 1x1 tracking pixel embedded in page
[...]
<img src="//failure.etsy.com/status/images/beacon.gif?
beacon_source=fastly_origin_failure-etsy.com">
</body>
</html>


Failure Beacons
2. Request creates an access log line


Failure Beacons
3. Scrape them out minutely using logster
self.reg = re.compile('^S+(s:)? (?P<remote_addr>[0-9.]+),?
[0-9.,- ]+ [[^]]+] "GET /status/images/beacon.gif?
(beacon_)?source=(?P<source>S+) HTTP/1.d" d+ [d-]+ "(?
P<referrer>[^"]+)" "(?P<user_agent>[^"]+)" .*$')


Failure Beacons
4. Logster posts event counts to Graphite


Failure Beacons
4. Logster posts event counts to Graphite
5. Alert on Graphite graph in Nagios


Failure Beacons
▪ Client IP address can be geolocated


Failure Beacons
▪ Optional extra debugging information
[31/Oct/2013:07:06:42 +0000] "GET /status/images/
beacon.gif?beacon_source=fastly_origin_failure-etsy.com
&provider_error=Connection%20timed%20out
&server_identity=cache-ny57-NYC HTTP/1.1"


Failure Beacons
▪ Optional extra debugging information


Tracking Requests to Origin
GET / HTTP/1.1
User-Agent: curl/7.24.0
Accept: */*
X-Forwarded-Host: www.etsy.com
[...]
X-CDN-Provider: edgecast
[...]
Host: www.etsy.com


Backend Monitoring
▪ Vendor APIs to bring data in house


Backend Monitoring
▪ Logster on CDN provider header


Backend Monitoring
▪ Data in-house benefits include
-

Integration with our anomaly detection systems

-

Consistent and unified view of all CDN metrics

-

We control data retention period


Awareness
▪ Over 100 engineers
▪ Deploying 60 times a day
▪ Correlating external and internal services


Awareness


Awareness
Deploy lines


Frontend Monitoring
▪ Performance is important to us
▪ Monitoring overall site performance
▪ Monitoring performance by CDN provider
▪ Real User Monitoring on key pages to track page

performance


Frontend Monitoring
▪ Performance is important to us
▪ Monitoring overall site performance
▪ Monitoring performance by CDN provider
▪ SOASTA mPulse on key pages to track real user

page performance


Downsides

Debugging: What broke?
▪ MTTD/MTTR can be extremely low with this

system
▪ But not always


Debugging: What broke?
▪ Non technical member base
▪ Confusing and time consuming
▪ Amazing support team
▪ Log as much information as possible


http://www.ﬂickr.com/photos/sk8geek/4649776194

Conclusions/Takeaways

Great success
▪ 12 months in the benefits have far outweighed the

few downsides
▪ We’re continuing to evolve the system
▪ We’ll be sure to share our experience with the

community along the way


Links/Open Source
▪ cdncontrol
http://github.com/etsy/cdncontrol
http://github.com/etsy/cdncontrol_ui

▪ logster
http://github.com/etsy/logster

▪ CDN API to Graphite scripts
http://github.com/lozzd/cdn_scripts

Thanks!
Questions?

Integrating multiple CDN providers at Etsy - Velocity Europe (London) 2013

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