nova — Flavors: scenarios

sequenceDiagram
    participant A as Admin (openstack CLI)
    participant API as nova-api
    participant DB as API database
    participant K as Keystone
    participant Bus as Notification bus
    A->>API: POST /flavors {name, ram, vcpus, disk, os-flavor-access:is_public: false}
    API->>DB: INSERT flavors
    alt name or id already used
        DB-->>API: duplicate entry
        API-->>A: 409 Flavor with name … already exists.
    end
    API->>Bus: flavor.create
    API-->>A: 200 {flavor}
    A->>API: POST /flavors/{id}/os-extra_specs {hw:cpu_policy: dedicated} (2.86+)
    API->>API: validate against the registry
    alt invalid value or unknown key in a Nova namespace
        API-->>A: 400 Validation failed; …
    end
    API->>DB: INSERT flavor_extra_specs (retry on races)
    API->>Bus: flavor.update
    A->>API: POST /flavors/{id}/action {addTenantAccess: {tenant: P}}
    API->>K: check that project P exists
    API->>DB: INSERT flavor_projects
    API->>Bus: flavor.update
    API-->>A: 200 {flavor_access: [{flavor_id, tenant_id: P}]}

sequenceDiagram
    participant U as User of project P
    participant API as nova-api
    participant DB as API database
    participant S as nova-scheduler
    participant PL as Placement
    participant C as nova-compute (libvirt)
    U->>API: GET /flavors (sees public + flavors shared with P)
    U->>API: POST /servers {flavorRef, imageRef}
    API->>DB: SELECT flavor (visible to P, not disabled)
    alt not visible or disabled
        API-->>U: 400 Flavor … could not be found.
    end
    API->>API: check image min_ram / min_disk / size, flavor vs image hw:* conflicts
    API->>API: copy the flavor into the server (instance_extra.flavor cur)
    API-->>U: 202 {server}
    S->>PL: GET /allocation_candidates?resources=PCPU:n,MEMORY_MB:m,DISK_GB:d&required=…
    S->>PL: PUT /allocations/{server}
    C->>C: build the guest from the copy: pinning, huge pages, devices, cgroups (quota:*)

sequenceDiagram
    participant U as User
    participant API as nova-api
    participant Cond as nova-conductor / scheduler
    participant C as nova-compute
    U->>API: POST /servers/{id}/action {resize: {flavorRef: new}}
    alt same flavor
        API-->>U: 400 When resizing, instances must change flavor!
    else new flavor disabled or not visible
        API-->>U: 400 Flavor … could not be found.
    else disk = 0 and image-backed
        API-->>U: 400 … Resize to zero disk flavor is not allowed.
    end
    API->>API: quota check for the increase, image constraints against the new flavor
    API->>Cond: resize (new_flavor); server keeps old_flavor and new_flavor
    Cond->>C: prep / resize / finish, Placement holds old and new allocations
    U->>API: confirmResize (cur = new) or revertResize (cur = old) [inferred]

sequenceDiagram
    participant A as Admin
    participant API as nova-api
    participant DB as API database
    participant U as User
    A->>API: DELETE /flavors/{id}
    API->>DB: DELETE flavor_projects, flavor_extra_specs, flavors
    API-->>A: 202
    U->>API: GET /servers/{sid} (2.47+)
    API-->>U: 200 server.flavor = {original_name, vcpus, ram, disk, ephemeral, swap, extra_specs} from the server's copy
    U->>API: POST /servers/{sid}/action {resize: {flavorRef: <deleted id>}}
    API-->>U: 400 Flavor … could not be found.