Tale of a Rewrite: Lessons Learned Rewriting Ranger

"Build one to throw away. You will anyway." -Fred Brooks
Few of us are brave enough to follow this advice. And yet sometimes we have to start over to move forward. With Ranger, we faced that decision. This talk discusses the rationale for the rewrite and certain key considerations we had to make during the migration.

Transcript

1. Tale of a Rewrite Jess Martin
2. About Me
7. He has told you, O man, what is good; And what does the LORD require of you but to do justice, and to love kindness, and to walk humbly with your God. - Micah 6:8
9. Let’s talk tech...
12. Business Does the rewrite significantly benefit profitability?
13. Server  Costs 200.00% 400.00% 800.00% 1600.00% URLs  to  Monitor 500 1000 2000 4000 8000 URLs  Per  Box 25 25 25 25 25 Servers  Needed 20 40 80 160 320 Monthly  Cost $799.00 $1,598.00 $3,196.00 $6,392.00 $12,784.00 Annual  Cost $9,588.00 $19,176.00 $38,352.00 $76,704.00 $153,408.00 Pricing  Models Cost  per  URL  per  month $1.60 $1.60 $1.60 $1.60 $1.60 Price  per  URL  per  month $3.00 $3.00 $3.00 $3.00 $3.00 Margin  per  URL  per  month $1.40 $1.40 $1.40 $1.40 $1.40 Gross  Margin 87.73% 87.73% 87.73% 87.73% 87.73% Monthly  Gross  Profit $701.00 $1,402.00 $2,804.00 $5,608.00 $11,216.00 Monthly  Gross  Revenue $1,500.00 $3,000.00 $6,000.00 $12,000.00 $24,000.00 Annual  Profit $8,412.00 $16,824.00 $33,648.00 $67,296.00 $134,592 URLs Per Box 25 URLs to Monitor 500 Cost Per Server $39.95 Price Per URL $3.00 Spreadsheets!
14. The best developers understand the benefit to the business of the code they are writing. Assertion #1
15. Architecture Can you scale (and understand) the system’s architecture?
16. Start at the whiteboard Ranger Architecture Diagram Rails App Server Users Apps Dependencies Watchers Postgres (stored in Postgres for now) Dependency Statuses every 1 minute check dependencies write new status if needed, enqueue email Recon.Perform API Heroku User URLs being checked Email Queue (resque) Redis PostMark Emails User Terminal in App Repo User Browser Under Development curl heroku-ranger User App heroku addons:add ranger heroku addons:remove ranger heroku ranger heroku ranger dependencies:add heroku ranger watchers:add provision/deprovision
17. Research with spikes require 'typhoeus' require 'json' api_key = "81a11b50-fd5d-012f-2d86-705681b14663" # Create a hydra instance hydra = Typhoeus::Hydra.new(:max_concurrency => 5) hydra.disable_memoization # Get a batch of dependencies to check response = Typhoeus::Request.get("http://localhost:3000/missions/next.json?internal_api_key=#{api_key}") puts response.body exit unless (response.code == 200) && (response.body != "null") dependencies = JSON.parse(response.body) # Queue the HTTP requests checks = dependencies.collect do |dependency| request = Typhoeus::Request.new(dependency["url"], :timeout => 5000) hydra.queue request {:id => dependency["id"], :request => request} end # Run the HTTP requests hydra.run # Build the results hash results = [] checks.each do |check| response = check[:request].response result = { :id => check[:id], :code => response.code, :time => response.time, :curl_return_code => response.curl_return_code, :curl_error_message => response.curl_error_message }
18. Developers need to understand the overall architecture in order to make smart decisions at the code level. Assertion #2
19. Reliability Are you confident in the reliability of the rewrite?
20. TDD, duh.
21. One test to rule them all Ranger 1.0 Ranger 2.0
22. Staging First
23. Migration Will you be able to move everything to the new system?
24. The three biggest risks in web development are: billing, reporting, and migration. - Jason Rudolph
25. 50 active users. No downtime allowed. Checking uptime every 5 minutes. So, 5 minute window to make the move.
26. So...
27. It worked.
29. Questions?