CI CD Troubleshooting

CI/CD Troubleshooting Workflow

When asked to diagnose or fix CI/CD failures (e.g., "Why is CI failing on PR #999?", "Fix the failing build"), follow this workflow to identify the root cause and optionally implement fixes.

Contents

• How to use this skill
• Related skills
• Step 1: Identify the Failure
• Step 2: Fetch Relevant Logs
• Step 3: Diagnose Root Cause
• Step 4: Reproduce Locally (if applicable)
• Step 5: Report Findings or Fix
  • Option A: Diagnostic Report ("Why is CI failing?")
  • Option B: Implement Fix ("Fix the failing build")
• Step 6: Verify Fix
• Special Troubleshooting Considerations

How to use this skill

Attach this file to your Copilot Chat context, then invoke it with a failing PR number, branch, or CI run context. Use Option A for diagnosis-only requests and Option B when the user explicitly asks for a fix.

Related skills

• Test Debugging — deep-dive test failure analysis and flakiness fixes
• Development Workflow — full TDD execution when implementing CI fixes
• PR Readiness Review — final validation before opening or updating a PR

Step 1: Identify the Failure

1. Get CI Status:

   • For PRs: gh pr checks #999
   • For branches: gh run list --branch <branch-name> --limit 5
   • Note which jobs passed and which failed

2. Categorize the Failure Type:

   • Test failures - Unit tests, integration tests failing
   • Linter failures - Rubocop, YARD documentation issues
   • Build failures - Dependency installation, compilation errors
   • Timeout failures - Jobs exceeding time limits
   • Platform-specific failures - Failing on specific Ruby version or OS

3. Identify Specific Failing Steps:

   • Note the exact job name and step that failed
   • Record the Ruby version, OS, and other environment details

Step 2: Fetch Relevant Logs

CRITICAL: CI logs can be massive (100K+ lines) and exceed token limits.

1. Get the Run ID:

   gh run list --branch <branch> --limit 1 --json databaseId --jq '.[0].databaseId'
   

2. Fetch Failed Job Logs Only:

   gh run view <run-id> --log-failed
   

   This limits output to only failed jobs, making it manageable.

3. Extract Key Error Information:

   • For test failures: Look for stack traces, assertion errors, specific test names

   • For linter failures: Extract file names, line numbers, and violation types

   • For build failures: Find dependency errors or missing packages

   • Use grep to filter logs if still too large:

     gh run view <run-id> --log-failed | grep -A 10 -B 5 "Error\|FAILED\|Failure"
     

4. Avoid Full Log Downloads:

   • Do NOT use --log without --log-failed unless specifically requested
   • If logs are still too large, focus on the most recent or critical failure

Step 3: Diagnose Root Cause

Based on the failure type, investigate:

For Test Failures:

• Check if the test exists and what it's testing
• Look for recent changes that might have broken the test
• Consider environment differences (local vs. CI)
• Check for flaky tests (intermittent failures)

For Linter Failures:

• Run linters locally: bundle exec rubocop and bundle exec rake yard
• Identify specific violations from the log
• Check if violations are in files related to recent changes

For Build Failures:

• Check dependency versions in Gemfile and git.gemspec
• Look for platform-specific dependency issues
• Verify Ruby version compatibility

For Timeout Failures:

• Identify which test or step is timing out
• Check for infinite loops or performance regressions
• Consider if it's a resource limitation in CI environment

Step 4: Reproduce Locally (if applicable)

For PR Failures:

1. Fetch the PR branch:

   gh pr checkout #999
   

2. Run the failing tests locally:

   bundle exec bin/test <test-name>
   

3. Run linters:

   bundle exec rubocop
   bundle exec rake yard
   

For Branch Failures:

1. Checkout the branch.

2. Run full CI workflow:

   bundle exec rake default
   

Step 5: Report Findings or Fix

Determine the appropriate action based on the user's request:

Option A: Diagnostic Report ("Why is CI failing?")

Present findings to the user:

# CI Failure Diagnosis: <Branch/PR>

**Status:** <X of Y jobs failed>

## Failed Jobs
1. **<Job Name>** (<Ruby version>, <OS>)
   - **Step:** <failing step name>
   - **Failure Type:** <test/linter/build/timeout>

## Root Cause
<Explanation of what's causing the failure>

## Error Details
```
<Relevant error messages and stack traces>
```

## Recommendations
- <Specific fix suggestion 1>
- <Specific fix suggestion 2>

**Would you like me to implement a fix, or do you need more information?**

STOP here unless the user asks you to proceed with fixes.

Option B: Implement Fix ("Fix the failing build")

Proceed based on failure type:

• Test Failures: Use the full TDD workflow (Phase 1-3) to fix the failing tests
• Linter Failures: Fix violations directly, commit with appropriate message (e.g., style: fix rubocop violations in lib/git/base.rb)
• Build Failures: Update dependencies or configuration as needed
• Timeout Failures: Investigate performance issues, may require user guidance

For PR Failures on Someone Else's PR:

• You may not have push access to their branch
• Present the fix and ask user to either:
  • Push to the PR branch (if they have access)
  • Comment on the PR with suggested changes
  • Create a new PR with fixes

Step 6: Verify Fix

After implementing fixes:

1. Run Affected Tests Locally:

   bundle exec bin/test <test-name>
   

2. Run Full CI Suite:

   bundle exec rake default
   

3. Push and Monitor:

   • Push the fixes

   • Monitor CI to confirm the fix worked:

     gh run watch
     

4. Confirm Resolution:

   Fix implemented and pushed. Monitoring CI run...
   CI Status: <link to run>
   

Special Troubleshooting Considerations

Platform-Specific Failures:

• If tests pass on macOS but fail on Linux/Windows, document the difference
• Check for path separator issues (/ vs. \)
• Look for encoding differences
• Consider file system case sensitivity

Flaky Tests:

• If a test fails intermittently, note this in your diagnosis
• Run the test multiple times locally to confirm flakiness
• Suggest fixes for race conditions or timing issues

Permission Issues:

• If you can't push to a PR branch, clearly communicate this limitation
• Provide the exact commands or changes needed for the user to apply

Token Limit Management:

• Always use --log-failed to limit output
• If logs are still too large, use grep to extract errors
• Focus on the first failure if multiple failures exist
• Consider running tests locally instead of relying on full CI logs

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