Quick verdict
C3X and Kubecost are complementary, not competing. C3X estimates K8s infrastructure changes from Terraform (clusters, node pools, addons) before deploy. Kubecost allocates actual K8s costs to workloads/namespaces/teams from runtime metrics. Most K8s-heavy orgs use both.
The cluster vs Terraform split
Kubernetes cost questions split into two categories that need different tools:
Infrastructure-level (what C3X handles)
- What does this EKS cluster cost? ($73/month control plane + node fleet)
- What's the cost delta when I scale a node pool from 5 to 10?
- What does enabling Cluster Autoscaler change?
- What does adding a Fargate profile cost vs EC2 nodes?
- What's the cost of a new GKE Autopilot cluster vs Standard?
These are answered from Terraform: aws_eks_cluster, aws_eks_node_group, google_container_cluster, etc. C3X reads the configuration and estimates infrastructure cost.
Workload-level (what Kubecost handles)
- Which namespace is using the most CPU?
- What does the staging environment cost per month?
- Which pod consumes the most cluster resources?
- How much does this team's microservices cost?
- Where can I right-size resource requests/limits?
These need runtime metrics (CPU usage per pod, memory used per namespace). Kubecost reads from Prometheus and the cloud billing API to allocate infrastructure cost to workloads.
The integrated workflow
How K8s-heavy organizations use both tools together:
- Engineer opens PR adding a new node pool to the EKS cluster.
- C3X (in CI) comments: +$1,400/month for 5 new m6i.2xlarge nodes.
- Reviewer approves; PR merges.
- Two weeks later, Kubecost shows that the new node pool is 30% utilized — workloads only need 2 nodes, not 5.
- Engineer opens a follow-up PR scaling the pool to 2 nodes.
- C3X comments: -$560/month. PR merges. Kubecost confirms the new allocation is healthy.
Without C3X, the team would only realize the cost after the bill. Without Kubecost, they wouldn't know that workloads were underutilizing the new pool.
Where Kubecost wins
- Per-workload cost allocation: Slice cluster costs by namespace, deployment, label, or controller. Critical for chargeback and team-level FinOps.
- Right-sizing recommendations: From actual CPU and memory usage data, suggests reduced resource requests/limits.
- Cluster autoscaler integration: Reads from metrics to estimate the impact of scaling decisions.
- Multi-cluster aggregation (Enterprise): Aggregates costs across clusters in a single dashboard.
- Predictive cost forecasting: Based on usage trends, projects future cluster costs.
Where C3X wins
- Pre-deploy estimation: Catches cluster cost changes in PRs. Kubecost only sees them after deploy.
- Multi-cloud Terraform: Same tool estimates EKS, AKS, GKE clusters and the non-K8s infrastructure around them (RDS, ElastiCache, ALBs, etc.).
- No cluster install: Runs from a Terraform repo. Kubecost requires Prometheus + agents installed in each cluster.
- Fully offline mode: Required for air-gapped clusters. Kubecost typically needs internet for cloud billing API access.
Feature comparison
| Feature | C3X | Kubecost |
|---|---|---|
| Terraform pre-deploy estimation | Yes (primary) | No |
| Per-pod / namespace allocation | No | Yes (primary) |
| Runtime metrics integration | No | Yes (Prometheus) |
| Multi-cluster aggregation | Via Terraform | Yes (Enterprise) |
| Right-sizing recommendations | From Terraform | From metrics |
| EKS/AKS/GKE support | All three | All three |
| Self-hostable | Yes | Yes |
| Cluster install required | No | Yes |
| Cost model | Free (Apache 2.0) | Free CE / Paid Enterprise |
FAQ
Is Kubecost a competitor to C3X?
No. They solve different problems. Kubecost analyzes actual Kubernetes cluster usage to allocate costs per namespace/pod/deployment. C3X estimates Terraform changes (including aws_eks_cluster, aws_ecs_service, GKE, AKS) before deploy. Most K8s-heavy orgs use both.
Does Kubecost estimate Terraform changes?
No. Kubecost reads from running clusters via metrics and the cloud billing API. It doesn't analyze Terraform. For pre-deploy estimation of cluster resource changes, you need a separate tool (C3X or Infracost).
Can C3X allocate costs per Kubernetes namespace?
No. C3X works from Terraform — it sees the cluster as a single aws_eks_cluster or google_container_cluster. Per-namespace/pod allocation requires runtime data (pod CPU/memory consumption × time × node price) that only Kubecost or similar in-cluster tools can compute.
Is Kubecost free or paid?
Kubecost has a community edition (free, single-cluster, no historical retention) and Enterprise (paid, multi-cluster, longer retention, SSO, etc.). C3X is fully free Apache 2.0 for all features. Different commercial models.
How do C3X and Kubecost work together?
C3X runs in CI to estimate Terraform changes (new clusters, node pool changes, K8s addon changes). Kubecost runs in each cluster to allocate actual runtime costs per workload. Engineers see both: 'this change will cost +$X/month' (C3X) and 'this team's workloads currently cost $Y/month' (Kubecost).