aws_opensearchserverless_collection cost estimation

An aws_opensearchserverless_collection runs OpenSearch without managing data nodes. Capacity is measured in OpenSearch Compute Units (OCUs) at ~$0.24/OCU-hour, plus managed storage at ~$0.024/GB-month. The catch is the minimum: OpenSearch Serverless requires a baseline of OCUs — historically 2 for indexing and 2 for search — so a collection has a ~4-OCU floor that bills ~$701/month even at low usage.

That floor is the defining cost characteristic. Serverless scales OCUs up with workload, which is great for spiky search/analytics, but the minimum makes it expensive for small or intermittent workloads — where a small provisioned domain, or even no OpenSearch at all, can be cheaper. The break-even versus a provisioned domain depends on how much you'd otherwise run.

The levers: set OCU maximums to cap scale-out cost, use a single collection (with multiple indexes) rather than many collections each paying the floor, and confirm the workload is large or spiky enough to justify serverless over a right-sized provisioned domain.

c3x prices the collection from its OCU count, so the capacity-floor cost is visible before deployment.

Terraform example

A minimal but realistic configuration that C3X can estimate.

resource "aws_opensearchserverless_collection" "search" {
  name = "app-search"
  type = "SEARCH"
}

Pricing dimensions

What you actually pay for when you provision aws_opensearchserverless_collection.

Dimension	Unit	What's being charged
OpenSearch Compute Units	per OCU-hour	Capacity in OCUs at ~$0.24/OCU-hour, with a minimum floor (historically ~4 OCUs) billed continuously. $0.24/OCU-hour → 4-OCU minimum ≈ $700.80/month
Managed storage	per GB-month	Indexed data stored, billed per GB-month. ~$0.024/GB-month

Sample C3X output

The 4-OCU minimum capacity, 24/7:

aws_opensearchserverless_collection.search
└─ OpenSearch Compute Units (4 OCU)   2920 OCU-hours   $700.80
                                      Monthly          $700.80

Optimization tips

Common ways to reduce aws_opensearchserverless_collection cost without changing the workload.

Confirm the workload justifies the floor

Avoids the floor for small workloads

The ~4-OCU minimum (~$701/month) makes serverless expensive for small or intermittent search/analytics. For those, a right-sized provisioned aws_opensearch_domain — or no OpenSearch at all — can be far cheaper. Use serverless for large or spiky workloads where the auto-scaling earns the floor.

Set OCU maximums

Caps peak cost

Serverless scales OCUs up with load. Setting a capacity maximum caps worst-case scale-out cost so a query spike doesn't run up unbounded OCU-hours.

Use one collection with multiple indexes

~$701/month per avoided collection floor

Each collection pays the OCU floor. Hosting multiple indexes in a single collection (where access patterns allow) avoids paying the minimum multiple times.

Right-size storage retention

Per GB-month reduced

Managed storage bills per GB-month. Drop indexes you no longer query so storage (and the data OCUs must serve) doesn't grow unbounded.

FAQ

Why does OpenSearch Serverless cost so much at low usage?

Because of the OCU minimum. It requires a baseline of OpenSearch Compute Units (historically ~4) that bill ~$701/month continuously, even with little traffic. The serverless model auto-scales above that, but the floor makes it pricey for small or intermittent workloads.

Serverless or a provisioned OpenSearch domain?

Serverless for large or spiky search/analytics where auto-scaling earns the ~4-OCU floor. For small or steady workloads, a right-sized provisioned aws_opensearch_domain (which you can scale and reserve) is often cheaper than the serverless minimum.

How does c3x estimate the cost?

From the OCU count, pricing OCU-hours at the serverless rate (the minimum floor is the baseline). Managed storage is priced per GB-month on top.

Related resources

AWS

aws_opensearch_domain

Provisioned OpenSearch — often cheaper for small/steady workloads

`aws_opensearchserverless_collection` cost estimation