# Official sources

Use this reference only when you need source grounding for AWS service behavior or the detailed source list.

## AWS documentation

Use these as starting points, not as proof of the user's live AWS state:
- https://docs.aws.amazon.com/wellarchitected/latest/cost-optimization-pillar/welcome.html
- https://docs.aws.amazon.com/wellarchitected/latest/framework/cost-optimization.html
- https://docs.aws.amazon.com/wellarchitected/latest/framework/cost_cloud_financial_management.html
- https://docs.aws.amazon.com/wellarchitected/latest/framework/cost_manage_demand_resources.html

## Grounding rule

Official documentation explains AWS service behavior. It does not prove the user's current account, Region, quota, resource configuration, IAM boundary, pricing, entitlement, or operational state. Prefer read-only AWS MCP or CLI evidence, repository evidence, or sanitized user-provided evidence for current-state claims.

## Current MCP/documentation refresh (2026-06-02)

Service facts from official docs:
- The Well-Architected Cost Optimization Pillar focuses on avoiding unnecessary cost while meeting business outcomes.
- Cost optimization review areas include cloud financial management, expenditure awareness, cost-effective resources, demand/resource management, and continuous optimization.

Sampled live evidence:
- Read-only API availability sampling reported `WellArchitected+GetWorkload` as `isAvailableIn` in `us-east-1`, `us-west-2`, `eu-west-1`, and `ap-southeast-1`.
- Cost-review evidence still requires workload, billing, tagging, utilization, and commitment data from the user's account; Well-Architected API availability alone does not prove review status.

Review implications:
- Require spend owner, cost allocation/tags, unit economics, utilization, rightsizing, commitment coverage, idle resources, and risk of reliability/security regression before recommending savings.
- Do not treat Well-Architected answers or tool access as proof that cost risks are remediated.

# Safety Checklist

Use before recommending any resource deletion, Reserved Instance purchase, Savings Plans commitment, or billing configuration change.

## Non-negotiables

- Never recommend deleting resources, snapshots, AMIs, or volumes without explicit inventory confirmation and owner sign-off.
- Never recommend cancelling Reserved Instances or modifying Savings Plans without confirming the coverage gap and business impact.
- Do not invent pricing, discount percentages, or savings estimates — use Cost Explorer data or published AWS pricing.
- Require explicit user approval before purchasing RIs, Savings Plans, or modifying AWS Budget alert thresholds.
- Rightsizing recommendations must include confirmation that the workload owner has reviewed the utilization data.
- Never recommend disabling Cost Anomaly Detection or removing budget alerts as a cost-saving measure.

## Stress checks

- Is the resource confirmed idle (not just low utilization)?
- Has the RI/SP purchase been validated against the commitment term and instance family lock-in?
- Are the tagging changes backward-compatible with existing cost allocation reports?
- Will the Savings Plans discount cover the expected instance mix across all account families?
- What is the blast radius if the recommended Auto Scaling min-capacity change is wrong?

# Well-Architected Cost Optimization Review Guide

Use this reference for AWS Well-Architected Framework Cost Optimization Pillar reviews. In this repository, `aws-waf-cost-optimization-review` means Well-Architected Framework review, not AWS Web Application Firewall configuration.

## What people get wrong

The lazy story is:

> Cost optimization means find idle resources and buy commitments.

Wrong. Good cost review preserves business outcomes. Savings that degrade reliability, security, observability, or delivery speed are not automatically good recommendations.

Common bad assumptions:

- Current month spend alone proves waste.
- Low utilization means safe rightsizing.
- Reserved Instances or Savings Plans are safe if the discount is large.
- Untagged resources are minor accounting issues.
- Spot is always a cost win.
- Deleting logs, backups, or redundancy is acceptable savings.

## Cost-specific failure modes

- No owner, cost allocation tags, unit-cost metric, or budget accountability.
- Recommendations ignore seasonality, migration, incident recovery, test load, or business growth.
- Commitment purchase locks in wrong family/Region/account or hides architecture change plans.
- Rightsizing ignores burst, memory, I/O, latency, failover, or compliance requirements.
- Observability, backup, security, or resilience costs are cut without risk acceptance.
- Savings estimate uses list pricing or aggregates without amortized/unblended context.

## Minimum safe workflow

1. Confirm workload, payer/member account scope, monthly spend, business owner, unit economics, and cost target.
2. Break down cost by service, account, Region, usage type, operation, tag, and resource where supported.
3. Evaluate governance: tagging, budgets, anomaly detection, chargeback/showback, and owner accountability.
4. Separate quick wins from structural optimization, commitment strategy, and risky workload changes.
5. Estimate savings with assumptions, confidence, operational risk, and pillar tradeoffs.
6. Require owner approval before deletion, downscaling, commitment purchase, retention reduction, or architecture change.
7. Track recommendations as experiments with rollback criteria and post-change cost validation.

## Verification targets

- Cost Explorer/Billing data grouped by service, account, Region, usage type, operation, tag, and resource where available
- budget, anomaly detection, cost category, and tag coverage evidence
- utilization metrics, performance headroom, workload seasonality, and business-critical periods
- Savings Plans/RI coverage, utilization, expiration, and purchase constraints
- idle/underused resources with owner and purpose confirmation
- reliability/security/observability impact for any proposed savings action

## When to push back

Push back if the user asks to:

- recommend commitments without usage stability and roadmap evidence
- delete backups/logs/redundancy for savings without risk acceptance
- rights-size production from average utilization only
- blame teams from untagged or payer-level aggregates
- ignore security or reliability tradeoffs
- confuse this Well-Architected Framework review with AWS Web Application Firewall cost tuning

# Workflow and Output Contract

Use this reference when performing the full WAF Cost Optimization Pillar review or formatting the final assessment.

## Review domains

Work through these five cost optimization design principles:

1. **Cloud financial management** — Cost Explorer enabled, CUR in S3, Budgets per account/project, Cost Anomaly Detection active, tagging policy enforced
2. **Expenditure awareness** — 100% resource tagging (env, team, app, cost-center), Cost Allocation Tags in billing, charge-back / show-back reports
3. **Cost-effective resources** — Graviton vs x86 evaluation, instance family selection, S3 storage class usage, RDS instance type vs Aurora Serverless fit
4. **Usage optimization** — Auto Scaling for stateless compute, S3 Intelligent Tiering or lifecycle rules, Spot Instances for fault-tolerant workloads, dev environment auto-shutdown
5. **Rate optimization** — Savings Plans coverage (Compute > EC2 > SageMaker), Reserved Instances for database/cache, Committed Use Discounts, Hybrid Benefit (Windows/SQL)

## Safe workflow

1. **Frame scope**: accounts, Regions, top 5 services by spend, monthly total
2. **Gather evidence**: Cost Explorer by service/tag, Trusted Advisor cost checks, Compute Optimizer recommendations, current Savings Plans coverage
3. **Assess each principle**: identify gaps per principle with estimated monthly savings
4. **Prioritize findings**: by estimated monthly savings impact
5. **Quantify savings**: provide per-recommendation estimated range with confidence level
6. **Confirm before acting**: require approval for resource deletion, RI/SP purchase, or billing config changes

## Response shape

1. Scope: monthly spend, top services, current commitment coverage
2. Cost visibility and attribution assessment
3. Tagging compliance
4. Rightsizing and instance family opportunities
5. Commitment strategy (Savings Plans, RI coverage)
6. Spot and managed service adoption
7. Storage and data transfer optimization
8. Idle resource inventory
9. Prioritized savings opportunities (est. monthly $ impact)
10. Open risks and blockers