When dispatcher caching is not enough
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When dispatcher caching was no longer sufficient to address performance issues for a pharmaceutical company's iPad app and content authoring, a content delivery network (CDN) was implemented. The CDN improved performance by serving cached content closer to users globally, reducing latency significantly. Content was categorized and caching rules were defined to maximize cache hits while ensuring privacy. Authorization was handled at the edge to cache authorized user content. These changes resulted in a major performance improvement and reduced load on the origin servers.
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When dispatcher caching is not enough
- 1. When dispatcher caching is not enough… Jakub Wądołowski Senior Systems Engineer @ Cognifide
- 2. The What The Why The How Agenda
- 3. The What
- 4. It all started in 2012… www.flickr.com/photos/nasahqphoto/16327416694
- 5. To be perfectly honest, initially it was rather like that… www.flickr.com/photos/garryknight/5703519506
- 6. The client EU pharmaceutical company 75 offices across the globe Over 40 000 employees Medical products available worldwide (180+ countries) www.flickr.com/photos/worak/2258271659
- 7. Country specific brochureware websites for medical products iPad app for sales representatives Single point for content entry Multiple integration points (SSO, user/device authentication, etc.) CQ 5.5, upgrade to AEM 6.1 in progress Requirements
- 8. Main components Brochureware website iPad app AEM Authoring
- 9. Single datacenter in London (Rackspace) REST-like API for iPad app Integrations with local and remote services Logical architecture
- 10. Initially it was just Spain, Argentina and Sweden
- 11. 6 months later the number of countries was tripled
- 12. To finally reach 21 and it is still not over
- 13. The Why
- 14. “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
- 15. Latency, latency, latency… Way too high round trip times (RTT) Timeouts Broken streams Connection resets Poor Internet connections in some areas Problems
- 16. Solutions
- 17. It has been decided that Hong Kong is the way to go for us
- 18. There’s over 10 000 km between London and Buenos Aires…
- 19. …which is nearly the same distance as between London and Hong Kong
- 20. Client-server problems became server-server ones How we’re going to sync all the changes (both ways)? What about deployments? Do we have enough licenses? What’s the best way to implement content sharding? How long it will take to implement all of these things? When initial excitement was gone…
- 22. We can’t just cache more on dispatcher This is a very well known problem Let’s use the right tool to solve the problem the right way Content Delivery Network (CDN) is the way to go! The road to CDN
- 23. “(…) 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 CDN definition
- 24. AEM + CDN
- 26. That's not necessarily true nowadays… www.flickr.com/photos/halfrain/14410890555
- 27. Pay-as-you-go model Powered by Varnish Highly customizable (ability to upload your own VCL) 150 ms to purge – globally ~5 sec to change a config through the web API SSD powered servers connected to T1 networks Real-time insight what’s happening (graphs, logs, etc) Great support Why Fastly?
- 30. The How
- 31. Ok… how should I start? www.flickr.com/photos/kleuske/8004416109
- 33. grep, awk, sed - all of these are your friends Count your requests Leverage the power of log monitoring tools (ELK, Splunk, etc.) Plan your content structure carefully Logs and content structure
- 35. 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 Request patterns
- 36. Assign these patterns to multiple buckets www.flickr.com/photos/ddebold/15991919514
- 37. Public content Private content Content available for authorized users only Content groups/buckets
- 38. Reverse HTTP proxy In-memory time based cache Blazing-fast Big “state” machine Varnish Configuration Language (VCL) Full control of HTTP flow Varnish in 1 slide!
- 39. Cacheable methods: GET, HEAD Cacheable response codes: 200, 203 300, 301, 302 404, 410 “Cache-Control: private” if not defined otherwise General caching rules
- 40. Let’s start with the iPad app www.flickr.com/photos/pestoverde/15048774061
- 41. 3 request types REST API request Presentation request (ZIP files) Image request iPad – HTTP flows
- 42. 2 content groups Private For all authorized users 8 request patterns TTL varies from 10 minutes to 7 days 35/65 dynamic/static content (frequently changing JSON files vs PDFs/PNGs) All REST API responses are private iPad app content
- 43. Private content is cacheable What makes HTTP response private? It is tied up with user session – in other words HTTP request carried unique authorization cookie Private content
- 44. www.flickr.com/photos/hyku/368912557 Is it really safe to cache that type of content?
- 45. Varnish cache is a key-value store Default key: req.url + req.http.host req.url + req.http.host + sessionId = private cache space - voila! Private cache
- 49. 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 Dynamic content
- 53. Fastly exposes purge REST API Purge URL Purge Key Purge all assets marked with special “label” https://www.fastly.com/blog/surrogate-keys-part-1 Purge All Purge vs Soft Purge https://www.fastly.com/blog/introducing-soft-purge Content purging
- 55. Hit ratio: 49,9% Cache coverage: 66,1% Requests: 89K iPad app statistics
- 56. What about the speed? www.flickr.com/photos/129341635@N02/16609174727
- 57. Presentation downloads 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 Speed boost
- 60. Adding Set-Cookie to every response Auth cookie is not revoked in the browser after logout TBD Crimes against cacheability
- 61. “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
- 62. I was rather skeptical Way 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 CDN in front of authoring?
- 63. 3 content groups 36 request patterns TTL up to 14 days Mostly dynamic + static web GUI resources A lot of assets common for every logged in user CDN + AEM Author Request pattern Cachable? /apps/cq/core/content/login/.*(png|jpg|css|js)$ YES /libs/cq/i18n/dict.en.json YES /etc/.*.(png|woff|css|js|jpg|gif|ttf|svg|eot|swf|ico)$ YES /cf#/content/myapp/en/about.html NO
- 65. CDN knows nothing about user session The goal is to cache common content for successfully authorized users Authorize them at the edge! Authorize at the edge
- 67. 2nd auth cookie (token), readable by CDN HMAC function 2 auth cookies are tied together Reference implementation: https://github.com/fastly/token-functions Private key shared between AEM and CDN CDN can evaluate user session without request to AEM Auth tokens
- 70. Hit ratio: 96,3% Cache coverage: 45,7% Requests: 83K Author statistics
- 71. Adding Set-Cookie to every response Auth cookie is not revoked in the browser after logout “Vary: Cookie” usage Crimes against cacheability
- 73. Does every deploy involve full CDN cache purge? Nope! iPad presentations are packaged in a ZIP file and versioned Majority of authoring related cacheable assets stay untouched between deployments AEM deployments
- 75. 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 savings More than satisfying results Very small changes in the AEM app itself Happy client Summary