AWS Rightsizing

AWS Rightsizing Skill

Analyze resource utilization and identify right-sizing opportunities with anti-hallucination guardrails and reusable CloudWatch functions.

Relationship to other AWS skills:

• aws-rightsizing/ -> "What to resize" (anti-hallucination rules, utilization thresholds, savings estimates)
• aws/ -> "How to execute" (parallel patterns, CloudWatch statistics syntax, throttling)
• aws-pricing/ -> "How much things cost" (on-demand pricing via get_aws_cost)
• aws-billing/ -> "Current spend" (billing context, discount detection)

CRITICAL: Rightsizing Rules (Anti-Hallucination)

These rules are MANDATORY when analyzing resource utilization. Violating them produces incorrect recommendations that can cause outages.

Rule 1: Minimum 14-Day Observation Window

Short observation windows miss weekly patterns (batch jobs, weekend traffic, month-end spikes). Default --days 14, allow up to 90.

WRONG:  --days 3   -> Misses weekend batch jobs
WRONG:  --days 1   -> Captures only one day's pattern
CORRECT: --days 14 -> Captures at least 2 full weekly cycles

The _rs_parse_days helper enforces the 14-90 day range.

Rule 2: Burstable Instances (t-family) Need Credit Balance

A t3.micro at 5% avg CPU may be fine OR may be throttled with 0 credits. A burstable instance running out of CPU credits is effectively capped at baseline performance, causing latency spikes.

MANDATORY: For any t-family instance (t2, t3, t3a, t4g), always check CPUCreditBalance. If credit balance trends toward 0, the instance is NOT underutilized -- it is credit-starved and may need upsizing.

WRONG:  t3.micro avg CPU 5% -> "underutilized, downsize"
CORRECT: t3.micro avg CPU 5%, credit balance 0 -> "credit-starved, consider upsizing"
CORRECT: t3.micro avg CPU 5%, credit balance 144 -> "underutilized, downsize candidate"

Rule 3: Memory Metrics Require CloudWatch Agent

mem_used_percent is NOT available by default in CloudWatch. It requires the CloudWatch Agent (CWAgent namespace) to be installed and configured on the instance.

MANDATORY: If CWAgent namespace returns no data, report "memory data unavailable" -- do NOT assume memory is fine.

WRONG:  No memory data -> "memory is fine"
CORRECT: No memory data -> "memory data unavailable (CWAgent not installed)"

Rule 4: Peak vs Average -- Never Downsize on Average Alone

An instance with avg CPU 10% but max CPU 95% is a bursty workload. Downsizing would cause failures during peaks.

MANDATORY: Report BOTH Average AND Maximum statistics. Only flag for downsizing if max < threshold too.

WRONG:  avg CPU 10% -> "downsize"
CORRECT: avg CPU 10%, max CPU 22% -> "downsize candidate (both avg and max are low)"
CORRECT: avg CPU 10%, max CPU 95% -> "bursty workload, do NOT downsize"

Rule 5: Savings Estimates Use On-Demand Pricing Only

If the instance has RI/SP coverage, actual savings differ from on-demand-based estimates. Always caveat estimates.

WRONG:  "You will save $70/mo by downsizing"
CORRECT: "Estimated savings: $70/mo (based on on-demand rates; actual savings may differ if RI/SP coverage applies)"

Rule 6: Multi-AZ RDS Doubles Compute Cost

A db.r5.large Multi-AZ costs ~$365/mo, not ~$182/mo. The standby replica incurs the same compute charge.

MANDATORY: Check MultiAZ flag before estimating RDS costs.

WRONG:  db.r5.large -> $182/mo
CORRECT: db.r5.large, MultiAZ=true -> $365/mo
CORRECT: db.r5.large, MultiAZ=false -> $182/mo

Rule 7: GP2 vs GP3 Baseline IOPS

GP2 baseline IOPS = max(100, 3 x GB). GP3 baseline = 3000 IOPS at lower cost per GB.

A 100GB GP2 has 300 IOPS baseline. GP3 gives 3000 IOPS at $0.08/GB vs $0.10/GB. Always calculate both when evaluating EBS rightsizing.

WRONG:  "GP2 and GP3 have similar performance"
CORRECT: "100GB GP2: 300 IOPS baseline at $10/mo. 100GB GP3: 3000 IOPS baseline at $8/mo (10x IOPS, 20% cheaper)"

Rule 8: Lambda Memory Controls CPU Allocation

Reducing Lambda memory from 1GB to 256MB also cuts CPU by 4x. Duration may increase, negating savings. Check duration trend before recommending memory reduction.

WRONG:  "Lambda uses 200MB of 1GB, reduce to 256MB"
CORRECT: "Lambda uses 200MB of 1GB. Check duration: if avg duration is near timeout, reducing memory will increase duration and may increase cost."

Mandatory Pre-Analysis Checklist

Before writing ANY rightsizing analysis, verify ALL of the following:

• Observation window >= 14 days (see Rule 1)
• Burstable instances (t-family) checked for CPUCreditBalance (see Rule 2)
• Memory metrics checked via CWAgent namespace with graceful fallback if unavailable (see Rule 3)
• Both Average AND Maximum statistics reported for all metrics (see Rule 4)
• Savings caveated as "based on on-demand rates" (see Rule 5)
• Multi-AZ flag checked for RDS instances (see Rule 6)
• All cost figures include currency unit (USD)
• Parallel execution used for all CloudWatch queries (see aws/SKILL.md)

Rightsizing Script (get_rightsizing_aws.sh)

DO NOT read or modify the script file. Only source and call the functions.

SETUP (at the start of your script):

source ./_skills/connections/aws/aws-rightsizing/scripts/get_rightsizing_aws.sh

All functions enforce anti-hallucination rules: 14-day minimum window, parallel CloudWatch queries, TOON output format.

FUNCTION REFERENCE:

RECOMMENDED WORKFLOW (every rightsizing analysis):

1. Always run aws_rightsizing_ec2 first -- EC2 is typically the largest compute cost
2. Run aws_rightsizing_rds for database layer analysis
3. Run aws_rightsizing_ebs for storage optimization (especially GP2->GP3 migration)
4. Run aws_rightsizing_lambda if Lambda is a significant cost driver
5. Or run aws_rightsizing_summary for a unified view across all resource types
6. For savings estimates, run aws_rightsizing_ec2_savings and aws_rightsizing_rds_savings

Examples:

source ./_skills/connections/aws/aws-rightsizing/scripts/get_rightsizing_aws.sh

# EC2 utilization analysis (14-day default)
aws_rightsizing_ec2

# EC2 analysis with 30-day window in specific region
aws_rightsizing_ec2 --days 30 --region us-west-2

# EC2 savings estimates
aws_rightsizing_ec2_savings --days 30

# RDS utilization
aws_rightsizing_rds --days 14

# RDS savings estimates
aws_rightsizing_rds_savings --days 14

# EBS rightsizing (GP2->GP3 candidates)
aws_rightsizing_ebs --days 14

# Lambda memory/duration analysis
aws_rightsizing_lambda --days 14

# Full summary across all resource types
aws_rightsizing_summary --days 30 --region us-east-1

EC2 Instance Family Quick Reference

Approximate monthly on-demand costs in USD (us-east-1). Use to validate savings estimates.

Downsizing savings: Moving one size down within a family typically saves ~50% (e.g., m5.xlarge $140 -> m5.large $70 = $70/mo savings).

For instance types or RDS pricing not listed above, use get_aws_cost from the aws-pricing/ skill.

Common Errors

Output Format

Present results as a structured report:

Aws Rightsizing Report
══════════════════════
Resources discovered: [count]

Resource       Status    Key Metric    Issues
──────────────────────────────────────────────
[name]         [ok/warn] [value]       [findings]

Summary: [total] resources | [ok] healthy | [warn] warnings | [crit] critical
Action Items: [list of prioritized findings]

Target ≤50 lines of output. Use tables for multi-resource comparisons.

Counter-Rationalizations