Migrações em zero downtime com ruby. Nesta apresentação mostro um pouco do mindset na RD para o rollout de novas features ou migrações sem downtime.

1. ø downtime
Jônatas Davi Paganini
jonatas
jonatasdp

2. 8dev
teams

3. 10 deploys / day

4. RD Station

5. +2m mail / day

6. +700 external services
integrations

7. +N callbacks

8. Availability is
REQUIRED

9. 99,9%
99,5%
99,0%
98,6%
98,0%
97,0%
99,99%
00:43:00
03:36:00
07:12:00
10:00:00
14:24:00
21:36:00
00:04:32
Availability

10. 99.999???

11. availability =
( total_time - timeout / total_time ) * 100

12. ødowntime

13. mindset

14. NO schedule
maintenance

15. avoid: all || nothing

16. build reversible things

17. build incremental migrations

18. RubyConf 2012

19. compatible versions

20. http://shipit.resultadosdigitais.com.br/blog/
migrando-com-zero-downtime
talk is <cheap>!

21. show me the code!!!

22. Migration
add_column :people, :full_name, :string

23. Update data
Person.all.each do |person|
person.full_name = "#{person.first_name} #{person.last_name}"
person.save
end

24. 350 million updates!!!

25. WTF time?!

26. Let’s improve it!
Person.all.each do |person|
person.full_name = "#{person.first_name} #{person.last_name}"
person.save
end

27. Select RIGHT attributes!

28. Update 0.1
Person.select("id,first_name,last_name").each do |person|
person.full_name = "#{person.first_name} #{person.last_name}"
person.save
end

29. update_attribute instead of save

30. Update 0.2
Person.select("id,first_name,last_name").each do |person|
person.update_attribute "full_name", "#{person.first_name} #{person.last_name}"
end

31. find in batches

32. avoid transaction
overhead

33. Update 0.3
Person.select("id,first_name,last_name").find_in_batches do |people|
People.transaction do
people.each do |person|
person.update_attribute "full_name", "#{person.first_name} #{person.last_name}"
end
end
end

34. FAILURE resilient

35. Update 0.4
Person.where(full_name: nil).select("id,first_name,last_name").find_in_batches do |people|
People.transaction do
people.each do |person|
person.update_attribute "full_name", "#{person.first_name} #{person.last_name}"
end
end
end

36. explore connection pool

37. Update 0.5
update_sql = "UPDATE people set full_name ="
Person.where(full_name: nil).select("id,first_name,last_name").find_in_batches do |people|
People.transaction do
people.each(ActiveRecord::Base.connection_config[:pool]) do |person|
ActiveRecord::Base.connection_pool.with_connection do |conn|
set_full_name = conn.quote("#{person.first_name} #{person.last_name}")
conn.execute("#{update_sql} #{set_full_name} where id = #{person.id} ")
end
end
end
end

38. model hook

39. Model
class Person < ActiveRecord::Base
before_save :update_full_name
def update_full_name
self.full_name = "#{first_name} #{last_name}"
end
end

40. rollout control

41. Rollout
class Rollout
def enabled?(feature, context)
redis.sismember(feature, context)
rescue Redis::BaseError
false
end
def enable(feature, context)
redis.sadd(feature)
end
def disable(feature, context)
redis.srem(feature)
end
private
def redis
Redis::Namespace.new("rollout", redis: $redis)
end
end

42. rollout use

43. if:
before_save :update_full_name, if: -> { Rollout.enabled? "started_migration", "global" }

44. deploysteps

45. smoothly
steps

46. PR #1
add new column

47. PR #2
writeold & newcolumns

48. PR #3
migrate data

49. PR #4
read from new column

50. PR #5
remove old column

51. PR #6
remove rollout code, cache

52. Conclusion

53. Embrace migrations
● smoothly
● incremental
● safe
● resilient

54. Avoid migrations
● all || nothing
● ! roll outable features

55. REFERENCES
blog.codeship.com/rails-migrations-zero-downtime/
shipit.resultadosdigitais.com.br/blog/migrando-com-zero-downtime/
confreaks.tv/videos/railsconf2012-zero-downtime-deploys-for-rails-apps

56. ?

57. Thanks!
jonatas
jonatasdp
ideia.me
shipit.resultadosdigitais.com.br