LEARN. PRACTICE. GROW.Build a cost baseline that can be reconciled
Start with the period and management question. Amortized cost spreads commitment charges over the relevant period; an unblended chart can show an upfront payment on its charge date. Do not compare different bases to announce savings. Record currency, accounts, services, filters, and included credits and taxes. Resource tags need activation for cost allocation, and untagged costs still exist. Backfill can restore activation status for earlier periods, but it does not invent tag values that were never on resources. In the fictional case, a tag was assigned in August and activated later; requesting data from June does not reconstruct June and July. Make the unattributed share explicit and agree an allocation rule with owners, without presenting that rule as direct AWS measurement.
Test rightsizing against the business cycle
Low average CPU is a clue, not permission to reduce memory. A JVM can experience heap pressure, GC, or I/O dependencies during closing that a daytime average hides. Compute Optimizer can use memory collected by the CloudWatch agent or supported external integrations, including Dynatrace. Collection needs the expected name, namespace, and dimension; in a Linux CWAgent case, losing InstanceId prevents correct metric association. Confirm the observed period and include the monthly cycle and agreed failure condition. In the exercise, a fleet moves from three workers delivering 400 units per minute each to two. With demand of 650, normal total capacity of 800 appears sufficient, but one surviving worker leaves a shortfall of 250. Approve the change only after testing functional performance, failure headroom, and rollback.
Treat alerts as delayed signals
AWS Budgets can track costs, utilization, and coverage, but notification depends on billing data arriving. It is not an instantaneous spending ceiling. Cost Anomaly Detection also depends on that data; a newly created monitor or very recent usage cannot provide immediate evidence of no anomaly. For a task that can grow quickly, combine alerts with agreed operational limits, technical monitoring, and a response owner. Budget actions need their own configuration and can require manual approval. Preventing new creation does not automatically stop existing resources. From the management account, an action can apply an SCP to another account but cannot directly target EC2 or RDS instances in that other account for stopping. The PM should test scope, permissions, and operational consequences before automating a response that could disrupt closing.
Trace traffic and demonstrate savings
Lower instance cost can hide higher data transfer. For NAT, identify available hours, processed GB, and cross-zone traffic. Centralizing everything in one zone can reduce a fixed component while increasing another component or a failure dependency. For consumers in a VPC accessing S3 in the same Region, assess a gateway endpoint, associated tables, and policies. This endpoint type has no additional endpoint charge; that does not eliminate S3 service costs. Creating it without associating the application table can leave traffic on NAT. In the fictional case, compare the same functional cycle before and after, with normalized volume, latency, and errors. Record cost per completed work unit, total cost, and residual costs after retirement. Removing a resource needs an owner and evidence of disuse, and a recommendation becomes realized savings only after the outcome is observed.
worker_capacity_per_min = 400
demand_per_min = 650
proposed_workers = 2
normal_capacity = proposed_workers * worker_capacity_per_min # 800
failure_capacity = (proposed_workers - 1) * worker_capacity_per_min # 400
failure_shortfall = max(0, demand_per_min - failure_capacity) # 250
# Fictional measured linear capacities; not AWS quotas or a load test.A fictional team proposes reducing workers before monthly closing based on daytime CPU. APS demonstrates the capacity shortfall after failure and requests a representative rehearsal before the change. Forecast savings remain a hypothesis until the full cycle is measured.
Common pitfalls
Excluding untagged costs; inventing history through backfill; treating alerts as a cap; downsizing by CPU without memory; overlooking traffic and failure capacity.
Related topics: Usage commitments and capacity
Accept an optimization with comparable cost, functional evidence, and sufficient capacity under agreed conditions.
Reference: EC2 metrics in Compute Optimizer · SAP-C02