Azure Reservations

Currently Reservations apply to specific components of the following Resources:

1. Virtual machine
2. SQL Database
3. Azure Synapse Analytics (formerly SQL Data Warehouse)
4. Azure Cosmos DB
5. Azure Blob Storage
6. Azure Dedicated Host
7. Azure Database for MySQL
8. Azure Database for MariaDB
9. Azure Database for PostgreSQL
10. Azure Managed Disks
11. Azure Databricks
12. Azure Cache for Redis
13. Azure Data Explorer
14. SUSE Linux
15. Red Hat Plans
16. Azure VMware Solution by CloudSimple
17. Azure Red Hat OpenShift
18. App Services

Key points:

Purchase reservations based on your long-term usage pattern.

You can purchase reservations using API, PowerShell, or CLI. 

Reservation can be applied to a single resource group, a single subscription, or all subscriptions in the billing context. A resource group can have a single resource.

Reservation benefits are “use-it-or-lose-it” at hourly grain, except for Databricks reserved capacity. . Unused reserved hours don't carry over.
You can pay for a reservation up front or monthly. The total cost of up-front and monthly reservations is the same and you don't pay any extra fees when you choose to pay monthly.

You can buy a reservation in the Azure portal at https://portal.azure.com/#blade/Microsoft_Azure_Reservations/ReservationsBrowseBlade

Take an inventory of your consistent usage and determine if you plan to continue with same pattern or make changes.

You can also exchange reservations after purchase for another reservation of the same type, if your needs change. For example, you can exchange a “West US - D4 VM series” RI to an “East US - E8 VM Series” RI. 

An exchange cancels the current reservation without penalty and a new purchase is made in lieu.

Only the purchaser and the account owner have access to the reservation. You can add other people to the reservation after purchase using "Access control (IAM)".