reasoning-about-kubernetes-cost-reliability

name	reasoning-about-kubernetes-cost-reliability
description	Use when reviewing Kubernetes manifests for resource cost implications, overprovisioning waste, reliability gaps (single replica, no PDB, missing anti-affinity), or cost-vs-reliability tradeoff decisions. Use when someone asks "how much does this cost?" or "is this production-ready?"
allowed-tools	Read, Glob, Grep

Kubernetes Cost & Reliability Reasoning

Core principle: Every resource request has a dollar cost. Every reliability gap has an outage risk. Always quantify both.

Workflow

Step 1: Calculate Cost

Extract requests.cpu and requests.memory (not limits) for each container. Multiply by replicas.

Quick estimate: (CPU x $22 + Memory_GiB x $3) x replicas = monthly cost

See references/cost-calculation-formulas.md for per-provider pricing (AWS/GCP/Azure).

Step 2: Detect Waste

Signal	Threshold	Action
limits >> requests	limits > 3x requests	Flag overprovisioning risk
No resource requests	Missing entirely	Flag -- cannot calculate cost
High replica count	> 5 replicas without HPA	Question if static scaling needed
Unused storage	PVC without matching Pod mount	Flag orphaned storage cost

See references/right-sizing-guide.md for optimization heuristics.

Step 3: Evaluate Reliability

Check	Production Minimum	Risk if Missing
replicas >= 3	Required	No HA, single-point-of-failure
PodDisruptionBudget	Required	Node drain kills all Pods
Pod anti-affinity	Required	All replicas on same node = no HA
Liveness + readiness probes	Required	No auto-recovery from crashes
Topology spread constraints	Recommended	Zone failure takes entire app down

See references/reliability-patterns.md for HA patterns and SLA calculations.

Step 4: Present Tradeoff Table

Always present a table with columns: Option | Monthly Cost | Availability | Risk. Show current state, recommended state, and high-HA option with calculated dollar amounts and SLA percentages.

Red Flags -- STOP and Investigate

• Production namespace + replicas: 1 + no PDB
• CPU/memory requests missing entirely (cannot reason about cost)
• limits set but requests missing (limits become requests, likely unintentional)
• Storage class "gp3" or "premium" without justification for cost tier

Non-Negotiable Rules

1. Every analysis MUST include a dollar amount. "Significant resources" is not analysis. Calculate it.
2. Every reliability finding MUST include an SLA percentage. "Not highly available" is not analysis. Quantify it.
3. Always present cost AND reliability together as a tradeoff table. Never analyze one without the other.
4. Use the quick estimate formula inline -- do not defer to "see the reference file."

Common Mistakes

Mistake	Reality
"Resources look reasonable" without dollar amounts	Always calculate: (CPU x $22 + Mem_GiB x $3) x replicas
Noting "single replica" without SLA impact	Quantify: 1 replica = ~99.5%, 3 replicas = ~99.95%
Ignoring memory when only CPU seems high	Memory is often the larger cost driver
Not mentioning PDB for any multi-replica workload	PDB is required for safe node maintenance
Analyzing cost without reliability (or vice versa)	Always present both together in tradeoff table