osc-placement — Interactions

Interactions with other components — osc-placement — branch stable/2026.2

Branch stable/2026.2 @ 402610a21872 — repository https://opendev.org/openstack/osc-placement — analysed on 2026-10-28

A command-line process: no database, no bus, no cache. Two outbound exchanges.

System	Protocol	Library	Purpose
Keystone	HTTP	keystoneauth1 (session opened by openstackclient)	authentication (`--os-auth-type`, password or token) and catalog: lookup of the `placement` endpoint by `service_type`, `region_name` and `interface` (`osc_placement/plugin.py:36-43`)
Placement	HTTP/JSON	keystoneauth1 `Session.request` with `endpoint_filter`	every command (`osc_placement/http.py:55-67`)

Requests sent to Placement

Headers:
- OpenStack-API-Version: placement <version> and Accept: application/json (osc_placement/http.py:57-61);
- X-Auth-Token (session);
- Content-Type: application/json on bodies (keystoneauth json=).
Query strings: built by urlencode (osc_placement/resources/common.py:29-38) or params=. Repeated keys (several required, several member_of) are sent as several parameters.
Write sequences (read-modify-write) that rely on Placement's generations:
- allocation set (1.28+): GET /allocations/{c} → PUT /allocations/{c} with consumer_generation → GET /allocations/{c};
- inventory set --amend: GET …/inventories → PUT …/inventories with resource_provider_generation from the GET;
- trait set, inventory class set: GET /resource_providers/{uuid} to read generation → PUT;
- resource provider create: POST → GET <Location>.
- No retry on 409: the error is shown to the user.

Sample frame (recorded; the path is shown relative to the Placement endpoint): openstack --os-placement-api-version 1.21 allocation candidate list --resource MEMORY_MB=1024 --member-of <agg1>,<agg2>

GET /allocation_candidates?resources=MEMORY_MB%3A1024&member_of=in%3Ae53de0d4-945b-4f79-9656-04adca52a66c%2C2fd705f2-fe20-40c1-a9e6-0daf87a5222e HTTP/1.1
OpenStack-API-Version: placement 1.21
Accept: application/json
X-Auth-Token: …

All the requests observed (1,381), command by command, are in _rewrite/exchanges_stable-2026.2.json, and their summary in _rewrite/client-contract_stable-2026.2.md.

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