refactor(metrics): add podContainerReadyDuration and refine the logging

[zyy17]

Summary by CodeRabbit

• New Features

  • Introduced a new metric, podContainerReadyDuration, to monitor the time taken for a pod's container to become ready after starting.

• Bug Fixes

  • Improved logging for startup and ready durations for better clarity.

• Documentation

  • Updated comments to clarify the calculations for both startup and ready durations.

[coderabbitai]

Walkthrough

The changes introduce a new metric called podContainerReadyDuration in the pkg/metrics/metrics.go file. This metric tracks the duration from when a pod's container starts running until it is ready, using a histogram vector with various labels. The collectPodMetrics method is updated to calculate both the startup and ready durations for containers, while logging statements and comments are revised for clarity. The integration of the new metric is designed to fit within the existing framework without altering its overall structure.

Changes

File Path	Change Summary
pkg/metrics/metrics.go	Added new metric podContainerReadyDuration to track container readiness duration. Updated collectPodMetrics to calculate both startup and ready durations, and modified logging statements and comments for clarity.

Poem

In the meadow where metrics grow,
A new duration starts to flow.
From start to ready, time is tracked,
With clearer logs, no detail lacked.
Hopping through code, we celebrate,
Metrics that help us calibrate! 🐇✨

---

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[coderabbitai]

Actionable comments posted: 1

🧹 Outside diff range and nitpick comments (2)

pkg/metrics/metrics.go (2)

85-94: LGTM with a minor suggestion for the help text

The new metric declaration is well-structured and consistent with existing metrics. However, the help text could be more precise.

Consider updating the help text to be more specific:

-		Help: "The duration from pod started to container ready.",
+		Help: "The duration from when a container starts running until it becomes ready.",

---

220-234: Consider architectural improvements for duration calculations

While the implementation is correct, consider the following improvements:

1. Extract duration calculations into helper functions to centralize the logic
2. Consider adding metric labels cardinality limits to prevent memory issues in large clusters

Example helper function:

func calculateContainerDuration(start, end time.Time, metric *prometheus.HistogramVec, labels ...string) {
    duration := end.Sub(start)
    metric.WithLabelValues(labels...).Observe(duration.Seconds())
    return duration
}

📜 Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 3b0b025 and 1f2d734.

📒 Files selected for processing (1)

• pkg/metrics/metrics.go (3 hunks)

🔇 Additional comments (1)

pkg/metrics/metrics.go (1)

243-243: LGTM! Improved log message clarity

The updated log message better describes the duration being measured.