What you don't know about clouds could kill you!!!

A talk given at the Scottish Ruby Conference 2011 about pitfalls encountered and lessons learned as we built an app deployed on Google Sites and Heroku.

Transcript

2. What You Don't Know About Clouds Could Kill You!!!
3. What we learned about the cloud by building and scaling a corporate intranet.
4. — the ‘ External infrastructure Easy commissioning ! Easy scaling Less maintenance Focus on what makes your app different • • • •
5. But sometimes...
6. TIMTOWTDI (pronounced Tim Toady)
7. TIMTOWTDIBSCINABTE (pronounced Tim Toady Bicarbonate)
8. @tangleofwire gar@55degrees.co.uk
9. MINT
10. HR Interface HR Server Intranet Google Sites Google APIs
11. Scaling Eliminate N+1 queries Add database indexes Page, Fragment, Action caching Background jobs • • • •
12. Other best practices Metrics & useful debugging data Notifications & error numbers Monitoring • • •
13. Max load (many simultaneous web requests)
14. Intranet Google Sites
15. AJAX polling (are we there yet?)
16. i.Reduce number of HTTP calls
17. Annual leave Request View summary • •
18. HR Interface HR Server Intranet
19. API wrappers (separate the things that change)
20. Integration tests (how are you today?)
21. ii.Be prepared for APIs to change
22. People pages Directory HR API Google APIs • • •
23. HR Interface HR Server Intranet Google APIs
24. Sync (avoid unnecessary HTTP requests)
25. Timeouts (discard requests or retry later)
26. require 'net/http' url = URI("http://example.com/feed") req = Net::HTTP.new(url.host, url.port) req.read_timeout = HTTP_READ_TIMEOUT req.open_timeout = HTTP_OPEN_TIMEOUT
27. Exponential backoff (handle intermittent network problems)
28. times_tried = 0 max_retries = 5 begin times_tried += 1 feed = HRApi.get_employee_feed rescue => e if times_tried < max_retries sleep 4 ** times_tried retry end raise e, "max retries reached" end
29. Isolate components (one error shouldn’t stop everything)
30. Fail (and go to the pub cache)
31. iii.Expect services to fail
32. Other considerations HTTP caching Webhooks • •
33. HTTP caching (anything new?)
34. Intranet HR service GET /user/23 { user 23 + ETag } GET /user/23 + ETag 304 Not Modified
35. #users_controller def show @user = User.find(params[:id]) expires_in 24.hours if stale? (:etag => @user, :last_modified => @user.updated_at) respond_to do |wants| wants.html wants.xml { render :xml => @user } end end end
36. #client code def get_user u = User.find(23) return u if u.max_age < Time.now.utc headers = { 'If-None-Match' => u.etag, 'If-Modifed-Since' => u.last_modifed } ... data = request.get(path, headers) ... return u if response.code == 304 return u.update_attributes(data) end
37. Webhooks (have your people call my people)
38. Intranet HR service GET /generate_report? callback=/foo working... POST /foo { fascinating data }
39. iv.Reduce time and cost of HTTP calls
40. Rules of thumb Reduce number of HTTP calls Be prepared for APIs to change Expect services to fail Reduce time and cost of HTTP calls 1. 2. 3. 4.
41. Thanks $ git log --format='%aN' | sort -u @rogerbooth @mrloop @cframe @grahamsavage @douglasfshearer @aw221 @jaz303 @lenary @subblue
42. Questions?