Local CI × GitHub Actions

Hybrid CI That Plays to the Strengths of Both
Kaigi on Rails 2026 Day1

Transcript

1. Local CI × GitHub Actions Hybrid CI That Plays to the Strengths of Both @gogutan Kaigi on Rails 2026
2. About me @gogutan Tech Lead @ Catal Inc. Hobbies: English, competitive programming (AtCoder), watching baseball, mahjong
3. Catallog Learning management system for children studying English Students log their daily study on tablets and see their growth https://catal.jp/
4. Another talk from our team Emiko Ando (@siroemk) Day 1, 15:50–16:05 @ Lime Hall Modeling Catallog with our school staff, starting from Google Sheets
5. Our CI took about 10 minutes • A Rails app with ~150 models, built by 8 engineers
6. Our CI took about 10 minutes • A Rails app with ~150 models, built by 8 engineers • CI on GitHub Actions: ~10 min for every review request
7. Our CI took about 10 minutes • A Rails app with ~150 models, built by 8 engineers • CI on GitHub Actions: ~10 min for every review request • AI costs are rising → we want to cut other SaaS costs
8. Rails 8.1: Local CI ActiveSupport::ContinuousIntegration
9. Why not run CI on your own machine? • “Dev laptops are super fast these days. They're chronically underutilized. And you already own them.” — basecamp/gh-signoff https://github.com/basecamp/gh-signoff
10. 10m 39s → 1m 57s
11. GitHub Actions already runs jobs in parallel
12. Not a replacement, but a hybrid • Even a modest laptop is fast enough
13. Not a replacement, but a hybrid • Even a modest laptop is fast enough fi • Local CI + GitHub Actions, each where it ts
14. Not a replacement, but a hybrid • Even a modest laptop is fast enough • Local CI + GitHub Actions, each where it ts fi • After ~6 months: GitHub Actions runs halved (406 → 197/mo)
15. Today • 1. Setting up Local CI • 2. Making it fast • 3. Using GitHub Actions alongside • 4. Should we unify on bin/ci?
16. 1. Setting up Local CI
17. bin/ci and con g/ci.rb • Generated by rails new (Rails 8.1) fi • bin/ci just loads config/ci.rb
18. con g/ci.rb • A simple DSL • step "title", "command" fi • Runs from top to bottom
19. A summary with timings at the end
20. Replace the steps with your own fi • Static analysis rst, then tests
21. gh signo • Runs only when all steps pass f • Adds one green check, signoff, to the commit
22. “This commit passed CI on my machine”
23. Make signo the only required check ff Using rulesets? gh signoff install sets this up for you
24. No green check for untested code
25. But you could still sign o by hand # without running bin/ci… ff • $ gh signoff
26. One signo for the whole CI • “A single signoff is all you need for most projects.” — basecamp/gh-signoff https://github.com/basecamp/gh-signoff ff • Easier to combine with GitHub Actions (later)
27. 2. Making it fast
28. ① As is • All steps in series • RSpec in a single process
29. ① As is: 4m 57s
30. ② + parallel_rspec • RSpec has no built-in parallelism • parallel_tests: 8 processes, 8 test databases
31. ② 4m 57s → 2m 57s
32. Still, many steps use only one core
33. ③ group (Rails 8.2) • Backported early: only one require line changed
34. ③ + group • Sub-groups run in parallel • Steps inside a sub-group run in order
35. ③ 2m 57s → 1m 57s
36. Keep a multi-core step running at all times
37. Keep a multi-core step running at all times
38. 4m 57s → 2m 57s → 1m 57s
39. 3. Where do we still use GitHub Actions?
40. 3 cases Local CI can't cover • 1. Merging to main: the last line of defense (it also triggers our staging build)
41. 3 cases Local CI can't cover • 1. Merging to main: the last line of defense (it also triggers our staging build) • 2. Dependabot PRs: about 60 a month
42. 3 cases Local CI can't cover • 1. Merging to main: the last line of defense (it also triggers our staging build) • 2. Dependabot PRs: about 60 a month • 3. Manual runs: when your machine is busy
43. Keep the jobs, limit when they run • Push to main • Dependabot PRs • Manual runs
44. Two paths
45. Two paths
46. ff Only signo is required…
47. f Add a job that sets signo
48. cloud-ci-signo • Waits for the 5 jobs with needs f • Then sets signoff through the API
49. ff A Dependabot PR: signed o by Cloud CI
50. Gotcha: skipped jobs count as success • “A job that is skipped will report its status as "Success". It will not prevent a pull request from merging, even if it is a required check.” — GitHub Docs fl fl https://docs.github.com/en/actions/how-tos/write-work ows/choose-when-work ows-run/control-jobs-with-conditions
51. Don't name the job signo • Name it differently f • Set signoff explicitly, only on success
52. bin/cloud-ci • Start GitHub Actions in one command, just like bin/ci
53. 4. Why not run bin/ci on GitHub Actions too?
54. Run bin/ci on GitHub Actions • The Rails docs say bin/ci can run in the cloud too • “…can be run either locally or in the cloud.” — Rails API docs https://api.rubyonrails.org/classes/ ActiveSupport/ContinuousIntegration.html • So we tried it
55. We tried it
56. bin/ci is tuned to scale up
57. Larger runners: faster and a bit cheaper
58. Still, we keep them separate fi • Needs cloud-speci c tuning
59. Still, we keep them separate • Needs cloud-speci c tuning fi • Larger runners aren't covered by free minutes
60. Still, we keep them separate • Needs cloud-speci c tuning • Larger runners aren't covered by free minutes fi • One job: harder to see what failed, no per-job re-runs
61. Still, we keep them separate • Needs cloud-speci c tuning • Larger runners aren't covered by free minutes • One job: harder to see what failed, no per-job re-runs fi • → Not worth forcing them into one
62. Summary • Local CI + gh signoff: 10m 39s → about 2 min
63. Summary • Local CI + gh signoff: 10m 39s → about 2 min • GitHub Actions covers the rest, all ending in one signoff
64. Summary • Local CI + gh signoff: 10m 39s → about 2 min • GitHub Actions covers the rest, all ending in one signoff • Unifying on bin/ci is possible, but not worth forcing
65. Provide sharp knives • “Ruby includes a lot of sharp knives in its drawer of features. Not by accident, but by design.” — The Rails Doctrine https://rubyonrails.org/doctrine#provide-sharp-knives
66. Local CI is a sharp knife • Everyone gets the power to turn things green
67. Local CI is a sharp knife • Everyone gets the power to turn things green • No big problems so far
68. Local CI is a sharp knife • Everyone gets the power to turn things green • No big problems so far • No more waiting 10 minutes after opening a PR
69. Local CI is fast because we trust each other