tracing: nest per-command spans, drop cache-hit source-image spans

[mzihlmann]

Kaniko's build traces come out flat: pkg/timing parents every span to the root build span and throws away the child context, so operations that are nested in time render as overlapping siblings. The clearest symptom is the per-command initial FS snapshot appearing to run in parallel with the command it belongs to, which is impossible. This threads context through pkg/timing so a Timer can spawn child spans, gives command execution its own span, and hangs both the initial snapshot and the execute span under the command span. A command now reads as a parent bar with its sub-steps nested sequentially inside instead of a pile of overlapping bars.

Stacked on mz-otel-instrumentation.

Summary by CodeRabbit

• Performance
  • Improved execution timing and tracing for build commands and remote source-image retrieval.
  • Timing data now more accurately reflects active remote operations and nested command activity.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 61555e3a-bcbe-4bce-80d2-0db5026cf532

📥 Commits

Reviewing files that changed from the base of the PR and between 7630fed and 9d17997.

📒 Files selected for processing (3)

• pkg/executor/build.go
• pkg/image/image_util.go
• pkg/timing/timing.go

📝 Walkthrough

Walkthrough

The timing package now supports child spans. Build snapshot and command execution timing uses those spans. Source-image timing now covers only remote retrieval.

Changes

Timing instrumentation

Layer / File(s)	Summary
Child span creation pkg/timing/timing.go	Start uses shared span-start logic. The new StartChild function creates spans under valid parent spans and preserves existing no-op behavior.
Scoped operation timing pkg/executor/build.go, pkg/image/image_util.go	Filesystem snapshots and command execution use child spans. Remote source-image timing starts immediately before RetrieveRemoteImage.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• osscontainertools/kaniko#913: Both changes update command tracing and span creation in the executor and timing packages.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the tracing problem and implementation, but it omits the required checklist, reviewer notes, release notes, and issue reference.	Add the required template sections, complete the checklists, provide an issue reference when applicable, and state release-note impact or remove that section.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely identifies the two main tracing changes: nested command spans and removal of cache-hit source-image spans.
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.

✨ 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 mz-otel-span-nesting

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@pkg/image/image_util.go`:
- Around line 105-107: Ensure timing covers every remote image retrieval,
including the cache-miss path inside cachedImage and the direct
RetrieveRemoteImage call. Move the timing instrumentation to the shared
remote-retrieval boundary or add equivalent timing around the call within
cachedImage, while avoiding duplicate spans for a single request.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 6688ac6b-282f-4764-a270-10c66f1f04f7

📥 Commits

Reviewing files that changed from the base of the PR and between 7630fed and 9d17997.

📒 Files selected for processing (3)

• pkg/executor/build.go
• pkg/image/image_util.go
• pkg/timing/timing.go

[0hlov3]

LGTM