Agent Skills: Azure Cosmos DB library for Rust

Azure Cosmos DB library for Rust

Client library for Azure Cosmos DB NoSQL API — document CRUD, containers, and globally distributed data.

Use this skill when:

• An app needs to store or query documents in Cosmos DB from Rust
• You need CRUD operations on items with partition keys
• You need multi-region routing with RoutingStrategy
• You need key-based auth as an alternative to Entra ID

IMPORTANT: Only use the official azure_data_cosmos crate published by the azure-sdk crates.io user. Do NOT use the unofficial azure_cosmos or azure_sdk_for_rust community crates. Official crates use underscores in names and none have version 0.21.0.

Installation

cargo add azure_data_cosmos azure_identity tokio

Do not add azure_core directly to Cargo.toml. It is re-exported by azure_data_cosmos.

Environment Variables

COSMOS_ENDPOINT=https://<account>.documents.azure.com/ # Required for all operations

Authentication

use azure_identity::DeveloperToolsCredential;
use azure_data_cosmos::{
    CosmosClient, CosmosAccountReference, CosmosAccountEndpoint, RoutingStrategy,
};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Local dev: DeveloperToolsCredential. Production: use ManagedIdentityCredential.
    let credential: std::sync::Arc<dyn azure_core::credentials::TokenCredential> =
        DeveloperToolsCredential::new(None)?;
    let endpoint: CosmosAccountEndpoint = "https://<account>.documents.azure.com/"
        .parse()?;
    let account = CosmosAccountReference::with_credential(endpoint, credential);
    let client = CosmosClient::builder()
        .build(account, RoutingStrategy::ProximityTo("East US".into()))
        .await?;
    Ok(())
}

Client Hierarchy

| Client | Purpose | Access | | ----------------- | ------------------------- | --------------------------------------- | | CosmosClient | Account-level operations | CosmosClient::builder().build() | | DatabaseClient | Database operations | client.database_client("db") | | ContainerClient | Container/item operations | database.container_client("c").await? |

Core Workflow

use serde::{Serialize, Deserialize};
use azure_data_cosmos::CosmosClient;

#[derive(Serialize, Deserialize)]
struct Item {
    pub id: String,
    pub partition_key: String,
    pub value: String,
}

async fn crud(client: CosmosClient) -> Result<(), Box<dyn std::error::Error>> {
    let container = client
        .database_client("myDatabase")
        .container_client("myContainer")
        .await?;

    let item = Item {
        id: "1".into(),
        partition_key: "pk1".into(),
        value: "hello".into(),
    };

    // Create
    container.create_item("pk1", item, None).await?;

    // Read
    let resp = container.read_item("pk1", "1", None).await?;
    let mut item: Item = resp.into_model()?;

    // Update
    item.value = "updated".into();
    container.replace_item("pk1", "1", item, None).await?;

    // Delete
    container.delete_item("pk1", "1", None).await?;
    Ok(())
}

Key Auth (Optional)

Enable account key authentication with the feature flag:

cargo add azure_data_cosmos --features key_auth

RBAC Roles

For Entra ID auth, assign one of these built-in Cosmos DB roles:

| Role | Access | | ------------------------------------- | ---------- | | Cosmos DB Built-in Data Reader | Read-only | | Cosmos DB Built-in Data Contributor | Read/write |

Best Practices

1. Use DeveloperToolsCredential for local dev, ManagedIdentityCredential for production — the Rust SDK does not have DefaultAzureCredential
2. Never hardcode credentials — use environment variables or managed identity
3. Reuse CosmosClient — clients are thread-safe; create once, share across tasks
4. Use RoutingStrategy::ProximityTo — route to the nearest region for lowest latency
5. Always specify partition key for item operations — Cosmos DB requires it for all CRUD

Reference Links

| Resource | Link | | ------------- | ------------------------------------------ | | API Reference | https://docs.rs/azure_data_cosmos | | crates.io | https://crates.io/crates/azure_data_cosmos |