This document summarizes a presentation on content invalidation strategies for Apache Sling and content delivery networks (CDNs). It discusses different layers of caching from the content management system to the browser. It also covers various invalidation models and techniques for invalidating specific resources, related resources, and entire sections of cached content. Specific examples are provided for invalidating digital asset management assets, vanity URLs, reusable components, and browser caches. The importance of precise invalidation and planning for inclusion are emphasized.

1. APACHE SLING & FRIENDS TECH MEETUP
10-12 SEPTEMBER 2018
The underappreciated power of content invalidation
Jakub Wądołowski, Cognifide (@jwadolowski)

2. 2https://flic.kr/p/c7a8iE
There are only two hard things in Computer Science:
cache invalidation and naming things.
Phil Karlton

3. 3
HTTP caching

4. What can be cached?
4
▪ HTTP response (body & headers)
▪ What makes response cacheable?
▪ Static assets only?
▪ Body encoding matters
▪ gzip, deflate, br, …
https://flic.kr/p/EWtcyL

5. Caching layers
5
▪ AEM (custom in-memory cache)
▪ Dispatcher
▪ CDN
▪ Web browser
https://flic.kr/p/Vh2TXE

6. 6
Invalidation strategy

7. Invalidation models
7
▪ TTL-driven
▪ Event-driven
▪ Mix of both
https://flic.kr/p/Ra7cVb

8. Dispatcher invalidation
8
▪ 3 primary techniques
▪ by folder level (statfile)
▪ TTLs
▪ resource only
▪ Extras
▪ refetching
▪ custom script
https://flic.kr/p/mAYbSi

9. 9

10. Invalidation request
10

11. 11

12. Nothing fancy, huh?
12
▪ Plenty of possibilities
▪ handle related resources
▪ invalidate CDN’s cache
▪ push data to external systems
▪ …
https://flic.kr/p/qZygAC

13. 13
CDN invalidation

14. The plan
14
▪ High hit ratio & cache coverage
▪ Long TTLs (30+ days)
▪ AEM content changes reflected quickly
▪ Precise invalidation
https://flic.kr/p/7F4bHa

15. Content view
15
▪ Dispatcher mirrors AEM content structure
▪ SEO-optimized customer-facing URLs
https://flic.kr/p/7rstvj

16. Dispatcher cache
16
www.example.org
www.example.org/help/about-us
www.example.org/summer-sale
www.example.org/product1-xyz

17. CDN cache
17

18. CDN cache keys
18

19. 19

20. Invalidation APIs
20
▪ Multiple endpoints
▪ feature/authentication differences
▪ performance may vary
▪ Invalidation scope
▪ everything
▪ URL(s)
▪ tag
https://flic.kr/p/dgfRgD

21. DAM assets
21
▪ Sounds trivial?
▪ Renditions
▪ Alt texts
▪ Non-standard properties
https://flic.kr/p/9d2MRh

22. /content/dam/adaptto/image.jpg/jcr:content/renditions.1.json
22

23. /content/dam/adaptto/image.jpg/jcr:content/metadata.json
23

24. DAM invalidation script
24

25. Akamai API request
25

26. Alt text (1/3)
26

27. Alt text (2/3)
27
▪ Get all the pages that use given asset
▪ Query Builder API

28. Alt text (3/3)
28

29. Vanity URLs
29
▪ Each page can have a number of easy-to-
remember URLs
▪ Those pages are cacheable too
https://flic.kr/p/GDprQk

30. Vanity URLs (1/3)
30

31. Vanity URLs (2/3)
31

32. Vanity URLs (3/3)
32

33. Reusable components
33
▪ Common elements (i.e. header)
▪ SDI (Sling Dynamic Include) to the rescue
▪ SSI (Server Side Includes)
▪ ESI (Edge Side Includes)
https://flic.kr/p/dgghVK

34. 34

35. 35

36. Tag-based invalidation (1/4)
36
▪ Not everything can be wrapped into SSI/ESI
▪ Layout/templates
▪ HTML markup configs
▪ Is QueryBuilder the only option?
https://flic.kr/p/25LNnfK

37. Tag-based invalidation (2/4)
37

38. 38

39. Tag-based invalidation (3/4)
39

40. 40
Browser caching

41. Browser cache setup
41https://www.fastly.com/blog/understanding-vary-header-browser

42. Versioned clientlibs
42
▪ Generally a good idea
▪ Does it fit well into CDN setup?
https://flic.kr/p/9gTRKV

43. Cache-Control
43
▪ public/private
▪ max-age=<seconds>
▪ must-revalidate
▪ no-cache
https://flic.kr/p/5GCeGg

44. 44

45. We barely scratched the surface…
45
▪ API throttling
▪ Error handling
▪ Payload limits
▪ Non-obvious content references
https://flic.kr/p/pSB1rM

46. Lessons learned
46
▪ purge all is dangerous
▪ make invalidation as precise as possible
▪ plan SSI/ESI since the very beginning
▪ QueryBuilder calls may require extra indexes
https://flic.kr/p/dgge8U

47. 47
Thank you!