Cloud Cost Engineering and Open Source FinOps
Notes from the team building C3X. Cost estimation for Terraform, the economics of cloud infrastructure, and how to ship FinOps tooling without a SaaS gate.
ElastiCache vs MemoryDB cost: when durability is worth paying for
MemoryDB costs more than ElastiCache for the same node type and adds a per-GB data-written charge ElastiCache doesn't have. Here's the price difference, the durability you're buying, and when each is the right call.
RDS Proxy cost: is the always-on charge worth it?
RDS Proxy bills per vCPU of the database it fronts, continuously, whether or not connections flow. Here's how the charge works, when it pays for itself, and when it's overhead you can skip.
MWAA cost: why managed Airflow starts at $350/month
Amazon MWAA bills a continuous base environment fee with no scale-to-zero, so even an idle environment costs ~$350/month. Here's the cost breakdown, why the floor exists, and how to keep it down.
Azure SQL Managed Instance cost: the $1,460/month floor and how to lower it
SQL Managed Instance has a 4-vCore minimum, so even an idle instance starts around $1,460/month on General Purpose. Here's the full pricing breakdown, the Business Critical premium, and the four levers that actually cut the bill.
Aurora I/O Optimized: when it actually pays off
Aurora I/O Optimized eliminates per-I/O charges but adds ~30% to instance/storage rates. The break-even is around 25% I/O share of total cost. Here's the math, when to switch, and how to apply it in Terraform.
AWS cost allocation tags: the practical guide
The standard 5 tags every resource should have, the activation gotcha that hides historical data, enforcement via Terraform default_tags and Tag Policies, and the anti-patterns to avoid.
Azure Hybrid Benefit explained: up to 55% off Windows and SQL
AHUB lets organizations with Windows Server or SQL Server licenses (with Software Assurance) save up to 40% on Windows VMs and 55% on SQL workloads. Stacks with Reserved Instances for 70-80% total savings.
GCP Committed Use Discounts vs Sustained Use Discounts
SUDs are automatic (30% off steady workloads). CUDs require commitment (25-55% off). They don't stack. Here's the math, the break-even, and the optimal strategy: 3-year flexible CUDs on baseline, SUDs above, Spot for elastic.
Containers vs serverless: the cost crossover at 2-3M requests/day
Lambda wins for sporadic and event-driven workloads. Containers win for steady high-volume traffic. The crossover is around 2-3M requests/day for typical APIs. Here's the math, the workload archetypes, and a decision framework.
EBS gp3 vs io2: when each makes sense
For 95% of production workloads, gp3 is the right choice (cheaper, performant enough). Use io2 only for over 16K IOPS sustained, 99.999% durability, or Multi-Attach. Here's the pricing math and the migration playbook.
Self-hosting a cloud pricing API on a €4 VPS
How we serve a public AWS/Azure/GCP pricing API with 2.7M SKUs from a single small Hetzner VPS. Schema design, scraper architecture, and six months of operational lessons.
m5 vs m6i vs m7i: cost and price-performance compared
Hourly rates, performance per dollar, and migration paths for AWS general-purpose EC2 families. When to migrate to m7i, when to skip straight to Graviton m7g, and when older families still make sense.
Estimating AWS Lambda costs from Terraform
Lambda is the most mis-estimated AWS service. Here's why cost tools show $0 by default, what data to feed them for accurate numbers, and the four optimization levers that actually move the bill.
GKE Standard vs Autopilot: which mode for your workload
Autopilot bills per-pod (vCPU, memory, ephemeral storage). Standard bills per-node. The break-even is around 50-55% node utilization. Here's the actual pricing math with n2-standard-4 nodes, when each mode wins, and how to migrate without surprises.
S3 request fees explained: when they matter more than storage
PUT is $0.005/1K. GET is $0.0004/1K. For high-frequency small-object workloads, request fees can exceed storage fees by 100x. Here's the full request pricing matrix across all storage classes, when fees dominate, and the architectural patterns that keep them low.
Right-sizing EC2 instances: the 20/50 rule and full process
Right-sizing cuts steady-state EC2 spend 20-40% in one pass. The 20/50 rule (average under 20%, peak under 50%) finds candidates. Here's the full pipeline: gather metrics, decide size, validate against periodic peaks, deploy in waves with monitoring.
Azure VM types compared: B vs D vs E vs F series
B-series is burstable. D-series is general. E-series is memory-optimized. F-series is compute-optimized. Family selection drives the bill more than size. Here's the per-vCPU and per-GB pricing math, the decision flow, and the workloads each family wins on.
CloudWatch Logs cost optimization: cutting the $0.50/GB bill
Ingestion at $0.50/GB dominates CloudWatch Logs bills. Source-side filtering, structured logging, IA tier, and S3 migration for high-volume groups typically cut the bill 50-80%. Here's the full breakdown and migration playbook.
How to estimate Azure costs from Terraform
Estimate Azure costs from Terraform configurations including Reserved Instances, Azure Hybrid Benefit, Spot VMs, and Premium SSD tier mapping. Completes the cloud trilogy alongside AWS and GCP.
AWS Free Tier explained: what's free in 2026
Three categories of AWS Free Tier (12-months-free, always-free, trial offers) with the actual limits for each service. What stays free forever, what expires, what surprises new accounts.
DynamoDB on-demand vs provisioned: which mode to choose
On-demand bills per request, provisioned bills per capacity-hour. The break-even is around 25% utilization. Here's the actual math, the decision framework, and how to set up auto-scaling and Reserved Capacity for the lowest steady-state cost.
RDS vs Aurora: cost decision framework
RDS is cheaper per instance hour; Aurora has more efficient storage and built-in replicas. Here's when each one wins, including Aurora I/O Optimized, Aurora Serverless v2, and Reserved Capacity options.
AWS Lambda cold starts: cost vs latency trade-off
Cold starts are mostly a latency problem, not a cost problem (except for Java). Here's when they matter, what each runtime's typical cold start looks like, and when Provisioned Concurrency or SnapStart pay for themselves.
How to estimate GCP costs from Terraform
Estimate Google Cloud costs from Terraform configurations with sustained-use discounts applied automatically, Committed Use Discounts via usage file, and Spot VMs detected from the resource. No GCP credentials required.
S3 storage class comparison: when each tier wins
Six S3 storage classes spanning 99x in per-GB price. Here's when Standard, Intelligent-Tiering, Standard-IA, One Zone-IA, Glacier Instant Retrieval, Glacier Flexible Retrieval, and Deep Archive each make sense, with lifecycle policy patterns.
AWS data transfer costs explained
The most opaque part of the AWS bill, broken down. Internet egress, cross-region, cross-AZ, NAT processing, CloudFront, VPC endpoints. The five biggest cost surprises and how to fix them.
EKS vs ECS: total cost comparison
The honest cost comparison between EKS and ECS, including control plane fees, Fargate vs EC2 trade-offs, and when each platform makes financial sense. With concrete numbers from a 10-service production fleet.
Reserved Instances vs Savings Plans: which to buy
Compute Savings Plans, EC2 Instance Savings Plans, Standard and Convertible Reserved Instances. The actual discount math, what each one covers, and a decision framework for which commitment to buy.
AWS Spot instances: when do they actually save money?
Spot instances offer 50-90% discounts but can be reclaimed with 2 minutes notice. Here's when they're worth it, how to handle interruptions gracefully, and how to combine Spot with Savings Plans for the lowest total cost.
Budget guardrails in CI: blocking PRs that exceed cost limits
Cost regressions are a category of bug that production-quality teams catch automatically. Here's how to add a budget gate to GitHub Actions, GitLab CI, Bitbucket, Atlantis, and Spacelift in five minutes.
CloudFormation cost estimation: the missing piece
How to estimate the monthly cost of a CloudFormation template before deploying. SAM templates, CDK output, nested stacks, and the patterns that work for migrating an existing CloudFormation workflow.
Air-gapped Terraform cost estimation for regulated environments
Federal, defense, and regulated industries can't use SaaS-based cost tools. Here's how to set up fully offline Terraform cost estimation for IL5/IL6, GovCloud, and classified environments.
AWS NAT Gateway costs: 3 alternatives that actually save money
NAT Gateway is the second-most-expensive AWS resource for many production workloads. Here's how to cut its cost by 60-90% using free VPC Gateway Endpoints, paid Interface Endpoints, and NAT instances.
How to estimate AWS costs from Terraform before deploying
From a single CLI command to PR comments in CI that block over-budget merges, this is the practical guide to Terraform cost estimation. No AWS credentials, no terraform plan, no SaaS account.
When gp2 to gp3 actually saves money (and when it doesn't)
gp3 is 20% cheaper than gp2 with better baseline performance. The migration is in-place with no downtime. Here's exactly when it saves money, when it doesn't, and how to migrate safely at scale.
Infracost Alternative: Open Source Cloud Cost Estimation Without a SaaS
Honest comparison of C3X vs Infracost for Terraform cost estimation. Where each tool wins, full feature matrix, and a migration guide for teams switching off Infracost.