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When dispatcher caching is not enough…

Jakub WądołowskiSenior Systems Engineer @ Cognifide

twitter.com/jwadolowski

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Agenda

The What What was the problem about?

The Why Why we decided to go for Content Delivery Network (CDN)?

The How How it was implemented?

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THE WHAT

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It all started in 2012…

www.flickr.com/photos/nasahqphoto/16327416694

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To be perfectly honest, initially it was rather like that…

www.flickr.com/photos/garryknight/5703519506

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The client

EU pharmaceutical company75 offices across the globeOver 40 000 employeesMedical products available worldwide (180+ countries)

www.flickr.com/photos/worak/2258271659

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Requirements

Country specific brochureware websites for medical productsiPad app for sales representativesSingle point for content entryMultiple integration points (SSO, user/device authentication, etc.)CQ 5.5, upgrade to AEM 6.1 in progress

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Main components

Brochureware website

iPad app AEM Authoring

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Logical Architecture

Single datacenter in LondonREST-like API for iPad appIntegrations with local and remote services

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Initially it was just Spain, Argentina and Sweden

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6 months later the number of countries was tripled

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To finally reach 21 and it is still not over

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THE WHY

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“Our team in Argentina complains that the app feels slow. They can’t download presentations sometimes. Could you please

investigate that?”

Mr B.

www.flickr.com/photos/r4vi/8640618489

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Problems

Latency, latency, latency…Way too high round trip times (RTT)TimeoutsBroken streamsConnection resetsPoor Internet connections in some areas

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Solutions

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When initial excitement was gone…

How we’re going to sync the content (both ways)?What about deployments?Do we have enough licenses to set up the new stack in a proper way?What’s the best way to implement content sharding?How long it will take to implement all of these things?

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PoC conclusion

www.flickr.com/photos/geishaboy500/2496995573

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The road to CDN

We can’t just cache more on dispatcherThis is a very well known problemLet’s use the right tool to solve the problem the right wayContent Delivery Network (CDN) is the way to go!

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CDN definition

“(…) CDN is a large distributed system of servers deployed in multiple data centers across the Internet. The goal of a CDN is to serve content to end-users with high availability and high performance. CDNs serve a large fraction of the Internet content today (..).”, Wikipedia

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AEM + CDN

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CDN, right?

www.flickr.com/photos/pictures-of-money/16678590844

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That's not necessarily true nowadays…

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Why Fastly?

Pay-as-you-go modelPowered by VarnishHighly customizable (ability to upload your own VCL)150 ms to purge – globally~5 sec to change a config through the web APISSD powered servers connected to T1 networksReal-time insight what’s happening (graphs, logs, etc)Great support

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Still not convinced?

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THE HOW

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Uhh… ok, how should I start?

www.flickr.com/photos/kleuske/8004416109

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The logs!

www.flickr.com/photos/martinbamford/5638834940

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Logs and content structure

grep, awk, sed - all of these are your friendsCount your requestsLeverage the power of log monitoring tools (ELK, Splunk, etc.)Plan your content structure carefully

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Look for patterns

www.flickr.com/photos/wwarby/4915777722

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Request patterns

If it is a GET request and starts with /bin/myapp/v[1-2]/a_string.json then it is X

All requests to /content/something/*/_jcr_content.zip end with 302 to /some/path/to/file.zip

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Assign these patterns to multiple buckets

www.flickr.com/photos/ddebold/15991919514

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Content groups/buckets

Public contentPrivate contentContent available for authorized users only

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Varnish in 1 slide!

Reverse HTTP proxyIn-memory time based cacheBlazing-fastBig “state” machineVarnish Configuration Language (VCL)Full control of HTTP flow

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General caching rules

Cacheable methods: GET, HEADCacheable response codes: 200, 203, 300, 301, 302, 410, 404“Cache-Control: private” if not defined otherwise

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Let’s start with the iPad app

www.flickr.com/photos/pestoverde/15048774061

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iPad content

2 content groups8 request patternsTTL varies from 10 minutes to 7 days35/65 dynamic/static content (frequently changing JSON files vs PDFs/PNGs)

All REST API responses are private

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Private content

Private content is cacheableWhat makes HTTP response private? It is tied up with user session – in other words HTTP request carried

unique authorization cookie

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Is it really safe to cache that type of content?

www.flickr.com/photos/hyku/368912557

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Private cache

Varnish cache is a key-value storeDefault key: req.url + req.http.hostreq.url + req.http.host + sessionId = private cache space - voila!

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Dynamic means uncacheable?

www.flickr.com/photos/gsfc/7402445224

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Dynamic content

Cache usually brings some trade-off Updates won’t be instantaneous TTL has to expire, or a purge request has to be triggered

CDN is the way to go if you accept this delay

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Content purging

www.flickr.com/photos/librariesrock/13522859053

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Content purging

Fastly exposes purge REST APIPurge URL Purge Key Purge AllPurge vs Soft Purge

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Results

www.flickr.com/photos/89228431@N06/11322953266

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iPad app statistics

Hit ratio: 48,4%

Cache coverage: 65,3%

Requests: 83K

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What about the speed?

www.flickr.com/photos/129341635@N02/16609174727

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Speed boost

Presentation download Europe: up to 21% faster South America: up to 50% faster APAC: up to 83% faster

API responses Europe: up to 60% faster South America: up to 40% faster APAC: up to 55% faster

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Issues?

www.flickr.com/photos/giuseppemilo/15414290956

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Crimes against cacheability

www.flickr.com/photos/alancleaver/4121423119

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Crimes against cacheability

Adding Set-Cookie to every response Auth cookie is not revoked in the browser after logout TBD

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“iPad app performance is much better now! But we still have some issues with authoring. It is really slow in some countries.”

Mr B.

www.flickr.com/photos/r4vi/8640618489

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CDN in front of authoring?

I was rather skepticalWay too dynamic to be considered cacheable?What kind of improvement we might get? 5-10%? Is it worth it?Don’t know how, but it has been decided to roll things out

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CDN + AEM Author

3 content groups36 request patternsTTL up to 14 daysMostly dynamic + static web GUI resourcesA lot of assets common for every logged in user

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Authorized only!

www.flickr.com/photos/rudyjuanito/5170435542

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Authorize at the edge

CDN knows nothing about user sessionThe goal is to cache common content for successfully authorized usersAuthorize them at the edge!

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Auth tokens

www.flickr.com/photos/cfortier/426610972

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Auth tokens

2nd auth cookie (token), readable by CDNHMAC function2 auth cookies are tied togetherReference implementation: https://github.com/fastly/token-functionsPrivate key shared between AEM and CDNCDN can evaluate user session without request to AEM

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www.flickr.com/photos/spacexphotos/16169087563

96,4%

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Author statistics

Hit ratio: 96,4%

Cache coverage: 45,1%

Requests: 97K

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Crimes against cacheability

Adding Set-Cookie to every response Auth cookie is not revoked in the browser after logout “Vary: Cookie” usage

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Summary

www.flickr.com/photos/andrewhurley/6254409229

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Summary

Traffic growth is no longer an issue Over 2 TB monthly reaches CDN servers ~5,5 million HTTP requests per month just ~570 GB was passed through to AEM

License, budget and time savingsMore than satisfying resultsVery small changes in the AEM app itselfHappy client

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jakub.wadolowski@cognifide.comgithub.com/jwadolowski

twitter.com/jwadolowski

linkedin.com/in/kubawadolowski/en

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