nova — Flavors: interactions

Flavors: interactions with other components — Nova — branch stable/2026.2

Branch stable/2026.2 @ 8df1922926dd — repository https://opendev.org/openstack/nova — analysed on 2026-10-28

System	Direction	What
API database (`nova_api`)	nova-api reads and writes	the flavor catalogue
Cell databases (`instance_extra.flavor`)	nova-api, conductor and compute write	each server's copy of its flavor
Message bus (versioned notifications)	nova-api publishes	`flavor.create`, `flavor.update`, `flavor.delete`
Placement	scheduler	resource and trait request built from the flavor
Keystone	nova-api	project check when access is granted

1. API database

Models in nova/db/api/models.py:225-281:

Table	Columns	Constraints
`flavors`	`id` int PK, `name` varchar(255) not null, `memory_mb` int not null, `vcpus` int not null, `root_gb` int, `ephemeral_gb` int, `flavorid` varchar(255) not null, `swap` int not null default 0, `rxtx_factor` float default 1, `vcpu_weight` int, `disabled` bool default false, `is_public` bool default true, `description` text, `created_at`, `updated_at`	unique `flavorid`, unique `name`
`flavor_extra_specs`	`id` int PK, `flavor_id` FK → `flavors.id`, `key` varchar(255) not null, `value` varchar(255)	unique (`flavor_id`, `key`), index (`flavor_id`, `key`)
`flavor_projects`	`id` int PK, `flavor_id` FK → `flavors.id`, `project_id` varchar(255) not null	unique (`flavor_id`, `project_id`)

No soft delete: rows are deleted (nova/objects/flavor.py:179-196).
Flavor and extra specs are written in one transaction at creation (nova/objects/flavor.py:143-175).
Extra-spec writes retry up to 10 times on duplicate-key races (nova/objects/flavor.py:95-129).
Reads join the extra specs eagerly (nova/objects/flavor.py:280-282).
name filtering uses the database's regular-expression operator, chosen from [database] connection (nova/objects/flavor.py:621-628) [inferred: the API database uses the same engine type as the cell database in normal deployments].

Representative list query for a non-admin user (nova/objects/flavor.py:600-653):

SELECT flavors.*, flavor_extra_specs.* FROM flavors
LEFT OUTER JOIN flavor_extra_specs ON flavor_extra_specs.flavor_id = flavors.id
WHERE (flavors.is_public = true
       OR EXISTS (SELECT 1 FROM flavor_projects
                  WHERE flavor_projects.flavor_id = flavors.id AND flavor_projects.project_id = :project_id))
  AND flavors.disabled = false
  AND flavors.memory_mb >= :minRam AND flavors.root_gb >= :minDisk
ORDER BY flavors.flavorid ASC, flavors.id ASC LIMIT :limit

2. The server's copy (cell database)

instance_extra.flavor holds {"cur": <Flavor>, "old": <Flavor>|null, "new": <Flavor>|null}, each flavor serialised as an oslo versioned object (nova_object.name: Flavor, version 1.2, nova_object.data with the fields of 01 § 3 plus extra_specs and projects) (nova/objects/instance.py:749-762). description is set to null in the copy.

Legacy instances kept the flavor in instance_system_metadata as keys instance_type_<field> and instance_type_extra_<key>, with old_ and new_ prefixes (nova/compute/flavors.py:45-61, nova/compute/flavors.py:142-202). Only hw:numa_cpus.* and hw:numa_mem.* extra specs were kept there.

3. Notifications

flavor.create, flavor.update (description, extra specs or access changes) and flavor.delete, priority INFO, publisher nova-api:<host> (nova/objects/flavor.py:575-596). The payload is FlavorPayload 1.4 (nova/notifications/objects/flavor.py:32-61): flavorid, name, memory_mb, vcpus, root_gb, ephemeral_gb, swap, rxtx_factor, vcpu_weight, disabled, is_public, extra_specs, projects, description.

4. Placement

The scheduler turns the server's flavor (and image) into one GET /allocation_candidates request (01 § 5, nova/scheduler/utils.py:80-203). For example, a flavor vcpus=4, ram=8192, disk=40, swap=1024, hw:cpu_policy=dedicated, trait:HW_CPU_X86_AVX2=required gives:

resources=PCPU:4,MEMORY_MB:8192,DISK_GB:41&required=HW_CPU_X86_AVX2

The allocation is written against the compute node and kept as long as the server lives on it. A resize holds both the old and the new allocation until confirm or revert. See reverse-spec-placement.

Source: reverse-spec-nova/03-flavors-interactions_stable-2026.2.md. The _rewrite/ and _inventory/ files are not published on the site.