Cosmos DB has always been one of my favorite tools in the Azure ecosystem. Its unique combination of global distribution, multi-model support, and industry-leading SLAs makes it a standout for building modern applications. When I discovered that Cosmos DB now offers a serverless mode, I was excited to give it a try. The promise of a truly pay-per-use model, with no costs incurred for idle resources, felt like a natural evolution for the platform — perfect for lightweight, unpredictable workloads or even just exploratory scenarios.

My initial experience was overwhelmingly positive. I set up a Cosmos DB account in serverless mode using Terraform, and the process was seamless. The provisioning worked perfectly, and even better, my billing reflected no costs until I actually started using the database. This makes serverless Cosmos DB an excellent option for experimenting with the platform or for scenarios where workloads are sporadic and don’t justify the expense of a provisioned throughput model. Understanding the Current Limitations

As I explored serverless Cosmos DB further, I encountered one limitation that gave me pause: the lack of support for multi-region replication. For me, the hallmark feature of Cosmos DB has always been its ability to effortlessly replicate data across regions. This feature enables active-active architectures and allows developers to create resilient, globally distributed applications with ease. Knowing that this capability is not yet available in serverless mode led me to reconsider how and where I would use it.

That said, I can see serverless Cosmos DB being a great fit for specific scenarios. Startups or small teams with limited budgets can take advantage of its zero-sunk-cost billing model to experiment and build prototypes without worrying about unexpected charges. For single-region workloads with low or variable traffic, serverless offers the flexibility to scale dynamically without the need to manage throughput provisioning manually.

Personally, if I’m working on lightweight single-region use cases, I tend to default to Azure Table Storage because of its simplicity and affordability. However, Cosmos DB serverless adds compelling capabilities like support for advanced query capabilities and multiple APIs (e.g., SQL, MongoDB, Cassandra) that may be worth considering even for smaller workloads. Although, I definitely want to check out the Graph Database API, this is albeit a bit of a niche workload but would definitely flip the bit even if I can’t have multi-region replication.

Exploring Terraform and Serverless Cosmos DB

To explore the serverless option more closely, I provisioned a Cosmos DB account using Terraform. The Terraform configuration was straightforward, and here’s the snippet I used to enable serverless mode:

resource "azurerm_cosmosdb_account" "main" {

  name                = "cosmos-${var.application_name}-${var.environment_name}"
  resource_group_name = azurerm_resource_group.main.name
  location            = azurerm_resource_group.main.location
  offer_type          = "Standard"
  kind                = "GlobalDocumentDB"

  consistency_policy {
    consistency_level       = "BoundedStaleness"
    max_interval_in_seconds = 300
    max_staleness_prefix    = 100000
  }

  capabilities {
    name = "EnableServerless"
  }

  geo_location {
    location          = var.primary_location
    failover_priority = 0
  }

}

One interesting note is that I hadn’t fully decided on my consistency policy. I typically default to eventual consistency, but for this exercise, I tried bounded staleness. Due to the lack of multi-region support, you will only be able to add a single geo_location block — and don’t even think about turning on multiple_write_locations_enabled . This is truly sad for me as these are my favorite features that light up active-active multi-region SaaS solutions that I love to design and build.

Looking Ahead

Cosmos DB Serverless is exciting but its target audience seems to overlap a lot with those that are likely to start out with something like Azure Table Storage. You know, somebody looking for a single region deployment with $0.00 sunk cost that scales with your traffic, has flexible schema structure and not a huge need for crazy query performance. I think I just described every startup on the planet. The question is, are the creature comforts and better performance that you get with Cosmos DB Serverless worth the higher cost vs. lower cost alternatives.

While serverless Cosmos DB may not yet offer multi-region replication, I’m optimistic about its potential. Its no-cost-for-idle-resources billing model opens up new possibilities for development and testing scenarios, as well as for workloads where traffic is unpredictable or infrequent. As the serverless offering evolves, I look forward to seeing additional features that make Cosmos DB such a powerful platform, like multi-region support, become available. In the meantime, I’ll continue to explore serverless for use cases where its current capabilities shine.

For developers building on Azure, Cosmos DB serverless represents an exciting option that complements the broader Azure ecosystem. It’s yet another example of how Azure continues to innovate and offer flexible solutions for diverse workloads.