Understand how the reservation discount is applied to Azure Cosmos DB

After you buy an Azure Cosmos DB reserved capacity, the reservation discount is automatically applied to Azure Cosmos DB resources that match the attributes and quantity of the reservation. A reservation covers the throughput provisioned for Azure Cosmos DB resources. It doesn’t cover software, networking, storage, or predefined container charges.

Reservation discount applied to Azure Cosmos DB accounts

A reservation discount is applied to provisioned throughput in terms of request units per second (RU/s) on an hour-by-hour basis. For Azure Cosmos DB resources that don't run the full hour, the reservation discount is automatically applied to other Cosmos DB resources that match the reservation attributes. The discount can apply to Azure Cosmos DB resources that are running concurrently. If you don't have Cosmos DB resources that run for the full hour and that match the reservation attributes, you don't get the full benefit of the reservation discount for that hour.

The discounts are tiered. Reservations with higher request units provide higher discounts.

The reservation purchase will apply discounts to all regions in the ratio equivalent to the regional on-demand pricing. For reservation discount ratios in each region, see the Reservation discount per region section of this article.

Reservation discount per region

The reservation discount is applied to Azure Cosmos DB throughput costs on an hour-by-hour basis. It's applied at either the single subscription or the enrolled/account scope. The reservation discount applies to meter usage in different regions in the following ratios:

Meter description Region Ratio
Azure Cosmos DB - 100 RU/s/Hour - AP Southeast AP Southeast 1
Azure Cosmos DB - 100 RU/s/Hour - AP East AP East 1
Azure Cosmos DB - 100 RU/s/Hour - EU North EU North 1
Azure Cosmos DB - 100 RU/s/Hour - KR South KR South 1
Azure Cosmos DB - 100 RU/s/Hour - EU West EU West 1
Azure Cosmos DB - 100 RU/s/Hour - KR Central KR Central 1
Azure Cosmos DB - 100 RU/s/Hour - UK South UK South 1
Azure Cosmos DB - 100 RU/s/Hour - UK West UK West 1
Azure Cosmos DB - 100 RU/s/Hour - UK North UK North 1
Azure Cosmos DB - 100 RU/s/Hour - UK South 2 UK South 2 1
Azure Cosmos DB - 100 RU/s/Hour - US East 2 US East 2 1
Azure Cosmos DB - 100 RU/s/Hour - US North Central US North Central 1
Azure Cosmos DB - 100 RU/s/Hour - US West US West 1
Azure Cosmos DB - 100 RU/s/Hour - US Central US Central 1
Azure Cosmos DB - 100 RU/s/Hour - US West 2 US West 2 1
Azure Cosmos DB - 100 RU/s/Hour - US West Central US West Central 1
Azure Cosmos DB - 100 RU/s/Hour - US East US East 1
Azure Cosmos DB - 100 RU/s/Hour - SA North SA North 1
Azure Cosmos DB - 100 RU/s/Hour - SA West SA West 1
Azure Cosmos DB - 100 RU/s/Hour - IN South IN South 1.0375
Azure Cosmos DB - 100 RU/s/Hour - CA East CA East 1.1
Azure Cosmos DB - 100 RU/s/Hour - JA East JA East 1.125
Azure Cosmos DB - 100 RU/s/Hour - JA West JA West 1.125
Azure Cosmos DB - 100 RU/s/Hour - IN West IN West 1.1375
Azure Cosmos DB - 100 RU/s/Hour - IN Central IN Central 1.1375
Azure Cosmos DB - 100 RU/s/Hour - AU East AU East 1.15
Azure Cosmos DB - 100 RU/s/Hour - CA Central CA Central 1.2
Azure Cosmos DB - 100 RU/s/Hour - FR Central FR Central 1.25
Azure Cosmos DB - 100 RU/s/Hour - BR South BR South 1.5
Azure Cosmos DB - 100 RU/s/Hour - AU Central AU Central 1.5
Azure Cosmos DB - 100 RU/s/Hour - AU Central 2 AU Central 2 1.5
Azure Cosmos DB - 100 RU/s/Hour - FR South FR South 1.625

Scenarios that show how the reservation discount is applied

Consider the following requirements for a reservation:

  • Required throughput: 50,000 RU/s
  • Regions used: 2

In this case, your total on-demand charges are for 500 quantity of 100 RU/s meter in these two regions. The total RU/s consumption is 100,000 every hour.

Scenario 1

For example, assume that you need Azure Cosmos DB deployments in the US North Central and US West regions. Each region has a throughput consumption of 50,000 RU/s. A reservation purchase of 100,000 RU/s would completely balance your on-demand charges.

The discount that a reservation covers is computed as: throughput consumption * reservation_discount_ratio_for_that_region. For the US North Central and US West regions, the reservation discount ratio is 1. So, the total discounted RU/s are 100,000. This value is computed as: 50,000 * 1 + 50,000 * 1 = 100,000 RU/s. You don't have to pay any additional charges at the regular pay-as-you-go rates.

Meter description Region Throughput consumption (RU/s) Reservation discount applied to RU/s
Azure Cosmos DB - 100 RU/s/Hour - US North Central US North Central 50,000 50,000
Azure Cosmos DB - 100 RU/s/Hour - US West US West 50,000 50,000

Scenario 2

For example, assume that you need Azure Cosmos DB deployments in the AU Central 2 and FR South regions. Each region has a throughput consumption of 50,000 RU/s. A reservation purchase of 100,000 RU/s would be applicable as follows (assuming that AU Central 2 usage was discounted first):

Meter description Region Throughput consumption (RU/s) Reservation discount applied to RU/s
Azure Cosmos DB - 100 RU/s/Hour - AU Central 2 AU Central 2 50,000 50,000
Azure Cosmos DB - 100 RU/s/Hour - FR South FR South 50,000 15,384

A usage of 50,000 units in the AU Central 2 region corresponds to 75,000 RU/s of billable usage (or normalized usage). This value is computed as: throughput consumption * reservation_discount_ratio_for_that_region. The computation equals 75,000 RU/s of billable or normalized usage. This value is computed as: 50,000 * 1.5 = 75,000 RU/s.

The 100,000 RU/s of reservation purchase would offset the 75,000 RU/s in AU Central 2. It leaves 25,000 RU/s to the FR South region. From the remaining 25,000 RU/s, a reservation discount of 15,384 RU/s is applied to the FR South region. The discount value is computed as: 25,000 / 1.625 = 15,384 RU/s. The remaining 34,616 RU/s in the FR South region are charged at the normal pay-as-you-go rates.

The Azure billing system will assign the reservation billing benefit to the first instance that is processed and that matches the reservation configuration. For example, it's AU Central 2 in this case.

To understand and view the application of your Azure reservations in billing usage reports, see Understand Azure reservation usage.

Next steps

To learn more about Azure reservations, see the following articles:

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