Derive GEM_HOME from ruby binary instead of hardcoding the version

[aramprice]

Problem

When the director was switched to Ruby 4.0, three job templates hardcoded ruby/4.0.0 as the GEM_HOME path suffix:

File	Hardcoded value
jobs/director/templates/env.erb	ruby/4.0.0
jobs/health_monitor/templates/bpm.yml	ruby/4.0.0
jobs/nats/templates/bpm.yml	ruby/4.0.0

Ruby 3.x always reports Gem.ruby_api_version as X.Y.0 (patch = 0), so the hardcoded suffix worked before. Ruby 4.0.x changed this — it now includes the patch version: 4.0.5, 4.0.6, etc. Gems are bundled into gem_home/ruby/4.0.6 but the director looked in gem_home/ruby/4.0.0, causing every Ruby-dependent job to fail to start:

not running after update: director, worker_1, worker_2, worker_3, health_monitor, credhub

Observed failures: brats-performance/564, bosh-disaster-recovery-acceptance-tests/568.

Fix

Replace the hardcoded version suffix with a shell command substitution that asks the ruby binary from the package itself:

$(ruby -e 'puts Gem.ruby_api_version')

ruby is already in PATH when these expressions are evaluated because each script sources runtime.env from director-ruby-4.0 first. The value is resolved at runtime and will automatically track any future Ruby 4.0.x patch bump without requiring a manual update.

Changes:

• jobs/director/templates/env.erb — fixes director, scheduler, sync-dns, metrics-server, and all worker processes (they all source this file)
• jobs/health_monitor/templates/health_monitor — dynamic GEM_HOME added after sourcing runtime.env
• jobs/health_monitor/templates/bpm.yml — hardcoded GEM_HOME removed (superseded by the startup script)
• jobs/nats/templates/bosh_nats_sync — dynamic GEM_HOME added after sourcing runtime.env
• jobs/nats/templates/bpm.yml — hardcoded GEM_HOME removed (superseded by the startup script)

[coderabbitai]

Walkthrough

Director, health monitor, and NATS runtime scripts now derive GEM_HOME from Gem.ruby_api_version instead of using Ruby 4.0.0-specific paths. The health monitor and NATS BPM configurations no longer define GEM_HOME, leaving BUNDLE_GEMFILE in their environment blocks.

Suggested reviewers: ay901246, benjaminguttmann-avtq, julian-hj

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly matches the main change: deriving GEM_HOME dynamically instead of hardcoding the Ruby version.
Description check	✅ Passed	The description covers the problem, fix, and affected files, but several template sections like tests, release notes, and breaking change are unfilled.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-ruby-4.0

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[Copilot]

Pull request overview

This PR fixes BOSH job startup failures caused by hardcoded GEM_HOME paths that assumed RubyGems’ API version always ended in .0 (e.g., 4.0.0). With Ruby 4.0.x now including patch in Gem.ruby_api_version (e.g., 4.0.6), the jobs must derive the correct suffix at runtime.

Changes:

• Replace hardcoded .../ruby/4.0.0 with .../ruby/$(ruby -e 'puts Gem.ruby_api_version') where GEM_HOME is set in startup scripts/templates.
• Remove GEM_HOME from BPM YAML env blocks for health_monitor and nats where it is now set by the executable wrapper script instead.
• Update the director’s shared env template so all director-related processes inherit the dynamic GEM_HOME.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
jobs/nats/templates/bpm.yml	Removes hardcoded GEM_HOME from BPM env for bosh_nats_sync (now set by wrapper script).
jobs/nats/templates/bosh_nats_sync	Sets GEM_HOME dynamically after sourcing the Ruby runtime env.
jobs/health_monitor/templates/health_monitor	Sets GEM_HOME dynamically after sourcing the Ruby runtime env.
jobs/health_monitor/templates/bpm.yml	Removes hardcoded GEM_HOME from BPM env (now set by wrapper script).
jobs/director/templates/env.erb	Makes director-wide GEM_HOME dynamic so all sourcing processes track Ruby patch bumps.

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