Azure Cosmos DB Deep Dive

# Set default consistency level for an account
az cosmosdb update \
  --name mycosmosdb \
  --resource-group myapp-rg \
  --default-consistency-level Session

# Override consistency per-request (SDK example)
# Python SDK:
# container.read_item(item="id1", partition_key="pk1",
#                     consistency_level=ConsistencyLevel.Strong)

# Check current consistency settings
az cosmosdb show \
  --name mycosmosdb \
  --resource-group myapp-rg \
  --query '{DefaultConsistency:consistencyPolicy.defaultConsistencyLevel, MaxStaleness:consistencyPolicy.maxStalenessPrefix}'

# Create a container with a partition key
az cosmosdb sql container create \
  --account-name mycosmosdb \
  --database-name myapp \
  --name orders \
  --resource-group myapp-rg \
  --partition-key-path "/customerId" \
  --throughput 4000

# Create a container with hierarchical partition keys (preview)
az cosmosdb sql container create \
  --account-name mycosmosdb \
  --database-name myapp \
  --name events \
  --resource-group myapp-rg \
  --partition-key-path "/tenantId" "/userId" "/sessionId" \
  --throughput 10000

# Set provisioned throughput
az cosmosdb sql container throughput update \
  --account-name mycosmosdb \
  --database-name myapp \
  --name orders \
  --resource-group myapp-rg \
  --throughput 10000

# Enable autoscale (scales between 10% and max RU/s)
az cosmosdb sql container throughput migrate \
  --account-name mycosmosdb \
  --database-name myapp \
  --name orders \
  --resource-group myapp-rg \
  --throughput-type autoscale

az cosmosdb sql container throughput update \
  --account-name mycosmosdb \
  --database-name myapp \
  --name orders \
  --resource-group myapp-rg \
  --max-throughput 20000

# Check RU consumption for a query (SDK response headers)
# Python: response.get_response_headers()['x-ms-request-charge']
# JavaScript: response.requestCharge

# Monitor RU consumption
az cosmosdb sql container throughput show \
  --account-name mycosmosdb \
  --database-name myapp \
  --name orders \
  --resource-group myapp-rg

# Add read regions
az cosmosdb update \
  --name mycosmosdb \
  --resource-group myapp-rg \
  --locations regionName=eastus failoverPriority=0 isZoneRedundant=true \
  --locations regionName=westeurope failoverPriority=1 isZoneRedundant=true \
  --locations regionName=southeastasia failoverPriority=2 isZoneRedundant=false

# Enable multi-region writes (multi-master)
az cosmosdb update \
  --name mycosmosdb \
  --resource-group myapp-rg \
  --enable-multiple-write-locations true

# Configure automatic failover
az cosmosdb update \
  --name mycosmosdb \
  --resource-group myapp-rg \
  --enable-automatic-failover true

# Trigger a manual failover (for DR testing)
az cosmosdb failover-priority-change \
  --name mycosmosdb \
  --resource-group myapp-rg \
  --failover-policies regionName=westeurope failoverPriority=0 \
  --failover-policies regionName=eastus failoverPriority=1

resource "azurerm_cosmosdb_account" "main" {
  name                = "mycosmosdb"
  location            = "eastus"
  resource_group_name = azurerm_resource_group.main.name
  offer_type          = "Standard"

  automatic_failover_enabled = true
  multi_region_write_enabled = false

  consistency_policy {
    consistency_level       = "Session"
    max_interval_in_seconds = 5
    max_staleness_prefix    = 100
  }

  geo_location {
    location          = "eastus"
    failover_priority = 0
    zone_redundant    = true
  }

  geo_location {
    location          = "westeurope"
    failover_priority = 1
    zone_redundant    = true
  }

  geo_location {
    location          = "southeastasia"
    failover_priority = 2
    zone_redundant    = false
  }

  tags = {
    Environment = "production"
  }
}

# Azure Functions Cosmos DB trigger (Python)
import azure.functions as func
import json
import logging

app = func.FunctionApp()

@app.cosmos_db_trigger(
    arg_name="documents",
    container_name="orders",
    database_name="myapp",
    connection="CosmosDBConnection",
    lease_container_name="leases",
    create_lease_container_if_not_exists=True,
)
def process_order_changes(documents: func.DocumentList):
    """Process changes from the orders container."""
    for doc in documents:
        order = doc.to_dict()
        logging.info(f"Order changed: {order['id']}, status: {order.get('status')}")

        if order.get("status") == "confirmed":
            # Trigger downstream processing
            send_confirmation_email(order)
            update_inventory(order)
            publish_analytics_event(order)

def send_confirmation_email(order):
    logging.info(f"Sending confirmation for order {order['id']}")

def update_inventory(order):
    logging.info(f"Updating inventory for order {order['id']}")

def publish_analytics_event(order):
    logging.info(f"Publishing analytics for order {order['id']}")

{
  "indexingMode": "consistent",
  "includedPaths": [
    { "path": "/customerId/?" },
    { "path": "/status/?" },
    { "path": "/createdAt/?" },
    { "path": "/total/?" }
  ],
  "excludedPaths": [
    { "path": "/metadata/*" },
    { "path": "/lineItems/*" },
    { "path": "/*" }
  ],
  "compositeIndexes": [
    [
      { "path": "/customerId", "order": "ascending" },
      { "path": "/createdAt", "order": "descending" }
    ],
    [
      { "path": "/status", "order": "ascending" },
      { "path": "/total", "order": "descending" }
    ]
  ],
  "spatialIndexes": [
    { "path": "/location/*", "types": ["Point", "Polygon"] }
  ]
}

# Enable TTL on a container (auto-delete old documents)
az cosmosdb sql container update \
  --account-name mycosmosdb \
  --database-name myapp \
  --name events \
  --resource-group myapp-rg \
  --analytical-storage-ttl -1 \
  --default-ttl 2592000  # 30 days in seconds

# View RU consumption metrics
az monitor metrics list \
  --resource "/subscriptions/SUB_ID/resourceGroups/myapp-rg/providers/Microsoft.DocumentDB/databaseAccounts/mycosmosdb" \
  --metric "TotalRequestUnits" \
  --interval PT1H \
  --start-time "2026-03-13T00:00:00Z" \
  --end-time "2026-03-14T00:00:00Z" \
  --aggregation Total