Cosmos DB as Event Store for Stream Processing

Question

Pulumi · Accepted Answer

In order to use Azure Cosmos DB as an event store for stream processing, you will need to set up a Cosmos DB account, a database, and a container. Azure Cosmos DB is a fully managed NoSQL database service provided by Microsoft Azure. It is designed to handle large amounts of data and provide low-latency, scalable solutions for web, mobile, gaming, and IoT applications. Cosmos DB supports multiple data models, including document, graph, key-value, and column-family. For event storing, you'll typically use the document model with a SQL API.

Here's a brief explanation of the resources we are going to create:

- **Cosmos DB Account**: This is the top-level resource within Azure Cosmos DB that provides the entry point to the service. You need an account before you can create databases or containers.

- **SQL Database**: A logical container for your data. This is where you define the structure of data that your application will store.

- **SQL Container**: Also known as a 'collection' in the DocumentDB API, this is where you store your data as JSON documents. You can define indexing policies, partition keys, unique keys, and more at this level.

We will use the `azure-native` Pulumi provider as it is the most current and supports native Azure resources. Below is a Pulumi program written in Python that provisions a Cosmos DB instance using the SQL API, which can then be used as an event store for stream processing:

```python
import pulumi
from pulumi_azure_native import documentdb as cosmosdb
from pulumi_azure_native import resources

# Create an Azure Resource Group
resource_group = resources.ResourceGroup("resource_group")

# Create an Azure Cosmos DB Account
cosmosdb_account = cosmosdb.DatabaseAccount("cosmosdbAccount",
                                            resource_group_name=resource_group.name,
                                            database_account_offer_type=cosmosdb.DatabaseAccountOfferType.STANDARD,
                                            locations=[cosmosdb.LocationArgs(
                                                location_name="West US",
                                                failover_priority=0,
                                                is_zone_redundant=False,
                                            )])

# Create a SQL Database inside our Cosmos DB Account
sql_database = cosmosdb.SqlDatabase("sqlDatabase",
                                    resource_group_name=resource_group.name,
                                    account_name=cosmosdb_account.name,
                                    options=cosmosdb.CreateUpdateOptionsArgs())

# Create a SQL Container inside our SQL Database
# The properties of the container can be set according to event storage requirements.
# The partition key should be chosen wisely to ensure data distribution and performance.
sql_container = cosmosdb.SqlContainer("sqlContainer",
                                      resource_group_name=resource_group.name,
                                      account_name=cosmosdb_account.name,
                                      database_name=sql_database.name,
                                      resource=cosmosdb.SqlContainerResourceArgs(
                                          id="events",
                                          partition_key=cosmosdb.ContainerPartitionKeyArgs(
                                              paths=["/eventType"],
                                              kind="Hash"
                                          )),
                                      options=cosmosdb.CreateUpdateOptionsArgs())

# Output the Cosmos DB endpoint and primary key for your application to use
connection_strings = pulumi.Output.all(resource_group.name,
                                       cosmosdb_account.name).apply(
    lambda args: cosmosdb.list_database_account_connection_strings(resource_group_name=args[0],
                                                                   account_name=args[1]))

primary_connection_string = connection_strings.apply(lambda c: c.connection_strings[0].connection_string)

pulumi.export('cosmosdb_endpoint', cosmosdb_account.document_endpoint)
pulumi.export('primary_connection_string', primary_connection_string)
```

The provided Pulumi program does the following:

- Defines an Azure Resource Group.
- Provisions an Azure Cosmos DB Account with the SQL (DocumentDB) API.
- Creates a SQL Database within the Cosmos DB Account.
- Defines a SQL Container within the database, which you can use to store your JSON documents. The container has a partition key configured, which is essential for ensuring that the database is able to scale and perform efficiently.
- Exports the Cosmos DB account endpoint and primary connection string. You'll use these in your application to connect to the database.

Remember to run `pulumi up` to deploy these resources after setting up your Pulumi and Azure environment. Please ensure you have the necessary permissions to create these resources in your Azure subscription.