Recommendations

CostGraph turns the metrics your agent collects into recommendations: downsize, upsize, terminate, or leave as-is. The recommendation is deliberately conservative — capacity safety always beats savings, and weak or contradictory evidence produces no recommendation.

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What it observes

Recommendations are computed from agent metrics over a rolling window:

• Observation window — the last 168 hours, with the most recent 24 hours tracked separately for recency.
• Idle window — a 7-day window, since terminating a VM demands stronger evidence.

Across that window it summarizes each signal by percentile (p50/p95/p99):

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Data-quality gates

Before any sizing happens, a VM must clear every gate below. If it fails one, CostGraph returns no recommendation and tells you why — this is the usual reason a VM shows no suggestion:

• Coverage ≥ 70% of the expected samples in the window. Sparse data → no recommendation.
• All required metrics present. A missing metric stops sizing entirely.
• Current price known. Candidate economics are meaningless without the baseline.
• Internally consistent metrics. Impossible or self-contradictory load (e.g. a huge run queue with near-zero CPU) is rejected as unreliable.

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How it sizes a VM

CPU is sized from observed cores used(load is a pressure signal, but it can be inflated by IO waits or pinned work). Required vCPU is the larger of:

• ceil(p95 cores used / 0.85) — keep the p95 at ~85% of the new vCPU count, and
• ceil(p99 cores used / 0.95) — keep the p99 at ~95%.

A utilization target (default 65%, bounded 50-80%) sets the headroom. CostGraph tightens that target for bursty workloads (high p99/p50 ratio), very small instances, and hosts seeing CPU steal from noisy neighbors. Memory must cover the observed p99 peak and projected growth — a linear trend extrapolated across the projection window plus a cushion — divided by a 75% target utilization, with a peak-plus-safety-margin floor so a VM is never sized below its measured peak.

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The recommendation it makes

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Idle detection

A VM is flagged to terminate only when all of these hold across the 7-day window — and then hold again in a second confirmation window:

• CPU utilization p95 ≤ 5% and cores used p95 ≤ 0.1
• Memory p99 ≤ 20% of the instance’s RAM
• Network throughput p95 ≤ ~1 KB/s
• Disk utilization p95 ≤ 1%
• Network and disk signals each have ≥ 70% coverage

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Cross-cloud recommendations

Beyond resizing within your current provider, CostGraph can compare a VM against equivalent instances on other providers. To avoid disruptive moves, a cross-cloud recommendation only surfaces when it is at least ~30% cheaper and clears latency and region-proximity guardrails.

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Confidence

Each recommendation carries a high / medium / low confidence, weighted mostly by data coverage, plus the absence of pressure and a stable CPU tail. Low-coverage windows are always low confidence.

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Cadence

Recommendations are re-evaluated continuously, roughly every day for active VMs (those whose agent has sent a heartbeat in the last few minutes). New hosts need to accumulate enough of the observation window before a first recommendation appears.