Server Flavours

In OpenStack, flavors define the compute, memory, and storage capacity of nova computing instances, virtual machines (aka servers).
To put it simply, a flavor is an available hardware configuration for a virtual machine. It defines the 
size of a virtual machine that can be launched.

According to OpenStack a flavor consists of the following parameters

Flavor ID
Unique ID (integer or UUID) for the new flavor. This property is required. If specifying ‘auto’, a UUID will be automatically generated.

Name for the new flavor. This property is required.

Historically, names were given a format XX.SIZE_NAME. These are typically not required, though some third party tools may rely on it.

Number of virtual CPUs to use. This property is required.

Memory MB
Amount of RAM to use (in megabytes). This property is required.

Root Disk GB
Amount of disk space (in gigabytes) to use for the root (/) partition. This property is required.

The root disk is an ephemeral disk that the base image is copied into. When booting from a persistent volume it is not used. The 0 size is a special case which uses the native base image size as the size of the ephemeral root volume. However, in this case the filter scheduler cannot select the compute host based on the virtual image size. As a result, 0 should only be used for volume booted instances or for testing purposes. Volume-backed instances can be enforced for flavors with zero root disk via the os_compute_api:servers:create:zero_disk_flavor policy rule.

Ephemeral Disk GB
Amount of disk space (in gigabytes) to use for the ephemeral partition. This property is optional. If unspecified, the value is 0 by default.

Ephemeral disks offer machine local disk storage linked to the lifecycle of a VM instance. When a VM is terminated, all data on the ephemeral disk is lost. Ephemeral disks are not included in any snapshots.

Amount of swap space (in megabytes) to use. This property is optional. If unspecified, the value is 0 by default.

Is Public
Boolean value that defines whether the flavor is available to all users or private to the project it was created in. This property is optional. In unspecified, the value is True by default.

By default, a flavor is public and available to all projects. Private flavors are only accessible to those on the access list for a given project and are invisible to other projects.

Extra Specs
Key and value pairs that define on which compute nodes a flavor can run. These are optional.

Extra specs are generally used as scheduler hints for more advanced instance configuration. The key-value pairs used must correspond to well-known options. For more information on the standardized extra specs available, see below

A free form description of the flavor. Limited to 65535 characters in length. Only printable characters are allowed. Available starting in microversion 2.55.