AzureAzure Cosmos DB for Apache CassandraDatabase

`azurerm_cosmosdb_cassandra_cluster` cost estimation

A managed Apache Cassandra cluster billed per node-hour by VM SKU. Three Standard_DS14_v2 nodes run ~$4,419/month, node count and SKU drive the whole bill.

An azurerm_cosmosdb_cassandra_cluster is Azure's managed Apache Cassandra (distinct from the Cosmos DB Cassandra API). It runs dedicated VM nodes, billed per node-hour by SKU, continuously. The default Standard_DS14_v2 is ~$2.018/node-hour, so three nodes work out to ~$4,419/month, a large, always-on commitment.

The bill is simply node_count × the SKU's hourly rate. Cassandra's distributed design means clusters run multiple nodes for replication and availability (three is a common minimum), so the cost is inherently in the thousands for production. The SKU sets per-node capacity and price: Standard_DS13_v2 (~$1.009/hr) and Standard_E16s_v5 (~$1.40/hr) are cheaper-per-node alternatives to DS14_v2.

The levers are node count (the replication/availability target, don't over-provision beyond your consistency and throughput needs) and SKU (right-size to the per-node workload). Managed disks attached to nodes add to it.

c3x prices the cluster from node_count and sku, so this high-cost resource shows its full monthly figure before deployment, important, given the scale.

Terraform example

A minimal but realistic configuration that C3X can estimate.

resource "azurerm_cosmosdb_cassandra_cluster" "main" {
  name                           = "cassandra-cluster"
  resource_group_name            = azurerm_resource_group.main.name
  location                       = azurerm_resource_group.main.location
  delegated_management_subnet_id = azurerm_subnet.cassandra.id
  default_admin_password         = var.admin_password

  sku        = "Standard_DS14_v2"
  node_count = 3
}

Pricing dimensions

What you actually pay for when you provision azurerm_cosmosdb_cassandra_cluster.

Dimension	Unit	What's being charged
Cassandra nodes	per node-hour	node_count × the SKU hourly rate, billed continuously. The entire cluster bill. $2.018/node-hour for Standard_DS14_v2 → 3 nodes ≈ $4,419.42/month
Managed disks	per disk-month	Storage attached to each node bills per managed-disk tier, on top of the node-hours.

Sample C3X output

Three Standard_DS14_v2 nodes, 24/7:

azurerm_cosmosdb_cassandra_cluster.main
└─ Cassandra nodes (Standard_DS14_v2 × 3)   2190 node-hours   $4,419.42
                                            Monthly           $4,419.42

Optimization tips

Common ways to reduce azurerm_cosmosdb_cassandra_cluster cost without changing the workload.

Right-size the node SKU

~$2,200/month switching DS14_v2 → DS13_v2 (3 nodes)

DS14_v2 is the priciest default at ~$2.018/node-hour. Standard_DS13_v2 (~$1.009) or Standard_E16s_v5 (~$1.40) cut per-node cost substantially if the workload fits, at 3 nodes, switching from DS14_v2 to DS13_v2 saves ~$2,200/month.

Match node count to replication needs

~$1,473/month per DS14_v2 node removed

Each node is a full-price VM. Run the node count your replication factor, consistency, and throughput actually require, not extra nodes for headroom that sits idle.

Reserve nodes for steady clusters

Up to ~60% on steady nodes

These are Azure VMs under the hood, so a reservation on the node SKU (1-3 year) discounts an always-on cluster significantly.

Consider the Cosmos DB Cassandra API for smaller workloads

Large for sub-scale workloads

Managed Cassandra runs dedicated nodes with a high floor. For smaller or variable workloads, the Cosmos DB Cassandra API (RU-based, serverless option) can be far cheaper than a multi-node dedicated cluster.

FAQ

Why is Managed Cassandra so expensive?

It runs dedicated VM nodes billed per node-hour, and Cassandra's distributed design means multiple nodes (three is a common minimum). At ~$2.018/node-hour for Standard_DS14_v2, three nodes is ~$4,419/month, the cost is inherently in the thousands for production.

How do I lower the cost?

Right-size the node SKU (DS13_v2 or E16s_v5 are cheaper than the DS14_v2 default), run only the node count your replication and throughput need, and reserve the nodes for a 1-3 year discount. For small workloads, the Cosmos DB Cassandra API may be far cheaper.

Is this the same as the Cosmos DB Cassandra API?

No. This is Azure Managed Instance for Apache Cassandra, dedicated VM nodes. The Cosmos DB Cassandra API is the RU-based, serverless-capable option. For smaller or variable workloads the API is usually cheaper; for large self-managed-style Cassandra, the managed cluster fits.

How does c3x estimate the cost?

From node_count and sku, pricing the node-hours. Given the scale, seeing the full monthly figure before deployment matters, an oversized SKU or extra node is thousands per month.

Related resources

Azure

azurerm_cosmosdb_account

The RU-based Cosmos DB (incl. Cassandra API), cheaper for smaller workloads

Estimate this resource in your own Terraform

Free, open source, no API key. C3X parses your Terraform and shows line-item cost for every resource, including azurerm_cosmosdb_cassandra_cluster.

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