Why we did not choose Microservices to replace a Legacy System

This is a presentation from microXchg Berlin 2018.

Abstract:

Whether you just started with programming or you're a professional: Chances are good you will not be happy with at least some of the code that you have written in the past. Mostly because you have some new perspective or learning. At the same time you must always keep in mind that legacy systems often drive business and are not easily replaced.

We will discuss bad decisions, discipline and how we used to generate more technical debt then can be handled. In this presentation we would like to share our personal story about how we tackled the legacy challenge in a pragmatic way, without jumping on the µ-services train for very good reasons. Despite not following all the current hype topics, we still ended up with a well automated and modern system architecture. We present our learnings and approaches for moving forward with a small team replacing the legacy puddle of mud with a new, shiny monolith over time.

Transcript

10. "With fejo.dk we want to provide the best experience brokering cottage homes in Denmark."
11. • Company started in 1993 • Small team (2 developers*, ~20 in total) • Working business model • Complex business logic and data Context *2015
12. Goals • Responsive Design • Re-enable team to feasible add new features • Attract new developers
13. Contraints • Existing system brings in the money • Minimise Risk • Limited amount of resources
15. –Old Klingon Proverb “Just extract a µ-Service for each of the identified bounded context and you're golden.”
17. SPOILER ALERT! !
18. We built a new Monolith
19. We built a new Monolith with Ruby on Rails…
21. …and are not finished yet !
22. Monolith µ-Services
23. Except, it's not!
24. THE FOLLOWING SLIDES HAVE BEEN APPROVED FOR ALL AUDIENCES BY THE BOARD OF BUZZWORDERY, INC. THE VIEWS ADVERTISED HAVE BEEN RATED ® SUBJECTIVE S www.yakshed.org CEOS REQUIRE ACCOMPANYING CERTIFIED DEVOP WHAT YOU ARE ABOUT TO SEE MAY CONTAIN SUBJECTIVE VIEWS OF THE SPEAKERS
25. #1
26. TEAM SIZE
29. Business Driven Development
30. Small company Small business needs ≭
33. Modularisation /ˌmɒdjʊlərʌɪˈzeɪʃn/
34. "That's not the motivation you're looking for."
35. –Wikipedia “Modular programming is a software design technique that emphasises separating the functionality of a program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of the desired functionality.”
36. Design decoupled components Design for Replacement Separation of Concern Systemic enforcement of modular structure
37. Systemic enforcement of modular structure
38. But…
39. • Requires more discipline • Supported by • Strict code reviews • Tests / Linter / Structure* • Imagine natural vs artificial border *https://medium.com/@dan_manges/the-modular-monolith-rails-architecture-fb1023826fc4
40. Separation of Concern
41. Legacy Encapsulation
42. • Dedicated areas in both Code and Data • Extend legacy system with "modern" API • Encapsulate and transform data between systems • Emulate the interface of the new system
43. Importer System
44. • Data includes • Facilities • Description • Images • Prices and availabilities • From over 40 different partner
48. Retrieval Aggregation Mapping Enrichment Persistence Queries DB Saves to DB Queries DB Saves to DB Exceptions go here
50. Retrieval Aggregation Mapping Enrichment Persistence
51. Retrieval Aggregation Mapping Enrichment Persistence Explicit Process Model
52. Retrieval Aggregation Mapping Enrichment Persistence Explicit interfaces & data format Exceptions go here
54. Design for Replacement
55. " in #
56. Legacy Encapsulation
57. Importer System • Easily remove partner who quit • Easily change specific importer logic • Remove temporary exceptions
58. Decoupled Components
59. Importer System
60. module ImageServer !class App < Sinatra::!Base configure :production do disable :show_exceptions end not_found do respond_with_404 end set :public_folder, File.join(File.dirname(__FILE__), '..', '..', 'public') set :available_image_sizes, !{ !!:mini => [106, 71], !:klein => [138, 92], !:mittel => [145, 108], !:mail => [175, 117], !:gross => [645, 430], !:grundriss => [617, nil], !:grundriss_mit_legende => [415, nil] !} before do expires !86400, :public # expire after one day end get '/' do File.read(File.join(settings.public_folder, 'index.html')) end !get %r{/hausbilder/(.*)_(#{settings.available_image_sizes.keys.join("|")})\.!(\w+)} do image_path = params[:captures][0] requested_size = params[:captures][1].to_sym image_extension = params[:captures][2] if settings.available_image_sizes.keys.include?(requested_size) original_filename = File.join(settings.public_folder, 'hausbilder', "#{!image_path}.#{image_extension}") if File.!exists?(original_filename) thumbnail = MiniMagick::Image.open(original_filename) width, height = settings.available_image_sizes[requested_size] unless image_extension.downcase.include?(!"svg") !!if requested_size == :grundriss_mit_legende || requested_size == :!grundriss thumbnail.combine_options do |c| c.resize "#{width}x>" end elsif requested_size != :gross || is_landscape?(thumbnail) thumbnail.combine_options do |c| c.resize "#{width}x#{height}^" c.gravity !"center" c.extent "#{width}x#{height}" end else thumbnail.combine_options do |c| c.resize "#{width}x#{height}" c.gravity !"center" c.bordercolor !"#ffffff" c.border "#{!width/2}x#{!width/2}" c.extent "#{width}x#{height}" end end end content_type thumbnail.mime_type status 200 expires !!86400*365, :public # expire after one week thumbnail.to_blob else respond_with_404 end end end get !"/photos/*" do |image_path| original_filename = File.join(settings.public_folder, 'dropbox_sync', !image_path.downcase) requested_width = request[!"w"].to_i if original_filename != photo_lookup(original_filename) if requested_width > 0 image = MiniMagick::Image.open(original_filename) image.combine_options do |option| option.resize "#{requested_width}x>" end content_type image.mime_type status 200 image.to_blob else send_file original_filename end else respond_with_404 end end helpers do def !is_landscape?(image) image[!"width"] >= image[!"height"] end def respond_with_404 content_type !"image/png" status 404 expires 600, :public_folder # expire after 10 Minutes File.read(File.join(settings.public_folder, 'images', '!missing_house_picture.png')) end def photo_lookup(filename) !if File.!exists?(filename) !return filename elsif File.extname(filename) == !".jpg" filename_jpeg = filename.gsub(/\.jpg$/, !".jpeg") return filename_jpeg if File.!exists?(filename_jpeg) end end end end end Image Server
62. We ended up with a quite modular system
63. Best Tool for the Job
64. Polyglot Programming and Persistence • Acknowledge different requirements within the application • We're building a web application ! • But: Harder to share knowledge
65. SELECT calculate_house_price(houses.price_data, $PEOPLE, $PETS) AS price FROM houses WHERE houses.id = $HOUSE_ID Stored Function Call
66. Modern Infrastructure requires µ-Services
67. Modern Infrastructure • Modern (Dev)Ops tooling • Automated infrastructure • Deployment Monolith • Still using services (Workers, Image Server)
68. Checklist Team size Business driven development Modularisation Best tool for the job
69. Outlook & Remarks
70. You can still deploy smallish services in a Monolith
71. The Modular Deployment Monolith
72. “…you shouldn't start a new project with µ-services, even if you're sure your application will be big enough to make it worthwhile.” Monolith First –Old Vulcan Proverb (by Martin Fowler) $
73. Future steps • Search & Scoring • Booking Process • Remaining parts of Import Process
74. Sum it up • Deliver business value with new system • Operate within reasonable risk for company • Apply modern infrastructure practises • Don't neglect your frontend
75. Aside: Frontend Architecture
76. $ tree app/components/house_search_button app/components/house_search_button ├── _house_search_button.html.haml ├── _house_search_button.scss ├── house_search_button.de.yml └── house_search_button.js <house-search-button class="HouseSearchButton"> <button name="button" type="submit" class="HouseSearchButton_button"> <p> <strong>30.485</strong> Häuser <em>anzeigen</em> </p> </button> </house-search-button>
77. • > 150 components • Explicit styling for each component • Usage of Custom Elements to isolate JavaScript • Events to communicate between components • ROCA style to reduce dependency on JavaScript
78. Thanks! Questions? Dirk Breuer (@railsbros_dirk) – Sebastian Cohnen (@tisba) PS: Find us at the StormForger booth!