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How the reservation discount is applied to Azure Cache for Redis

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After you buy an Azure Cache for Redis reserved capacity, the reservation discount is automatically applied to cache instances that match the attributes and quantity of the reservation. A reservation covers only the compute costs of your Azure Cache for Redis. You're charged for storage and networking at the normal rates. Reserved capacity is only available for premium tier caches.

How reservation discount is applied

A reservation discount is use-it-or-lose-it. So, if you don't have matching resources for any hour, then you lose a reservation quantity for that hour. You can't carry forward unused reserved hours.

When you shut down a resource, the reservation discount automatically applies to another matching resource in the specified scope. If no matching resources are found in the specified scope, then the reserved hours are lost.

Stopped resources are billed and continue to use reservation hours. To use your available reservation hours with other workloads, deallocate or delete resources or scale-in other resources.

Discount applied to Azure Cache for Redis

The Azure Cache for Redis reserved capacity discount is applied to your caches on an hourly basis. The reservation that you buy is matched to the compute usage emitted by the running caches. When these caches don't run the full hour, the reservation is automatically applied to other caches matching the reservation attributes. The discount can apply to caches that are running concurrently. If you don't have caches that run for an entire hour that match the reservation attributes, you don't get the full benefit of the reservation discount for that hour.

The following examples show how the Azure Cache for Redis reserved capacity discount applies depending on the number of caches you bought, and when they're running.

  • Example 1: You buy an Azure Cache for Redis reserved capacity for a 6-GB cache. Suppose you're operating a 13-GB cache that aligns with the other attributes of the reservation. In this case, you're billed the pay-as-you-go rate for 7 GB of your Azure Cache for Redis compute usage. Meanwhile, you receive the reservation discount for one hour of 6-GB cache compute usage.

In the following examples, assume that you purchased reserved capacity for a 26-GB Azure Cache for Redis. Additionally, the other attributes of the reservation align with the running cache.

  • Example 2: You run two 13-GB caches for an hour. The 26-GB reservation discount is applied to the compute usage of both caches.

  • Example 3: You run one 26 GB from 1 pm to 1:30 pm. You run another 26-GB cache from 1:30 to 2 pm. Both are covered by the reservation discount.

  • Example 4: You run one 26 GB from 1 pm to 1:45 pm. You run another 26-GB cache from 1:30 to 2 pm. You're charged the pay-as-you-go price for the 15-minute overlap. The reservation discount applies to the compute usage for the rest of the time.

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

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