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Use case

  • It will be very useful if the admin user could disable a child cell when the child cell needs to be maintained. Typically there would be 5 states: active, draining, testing, read-only and inactive
* Active would be the usual state.
* Draining would respond to queries, migrations and deletes but refuse new schedule requests.
* Testing would respond as Active but only when targeted with schedule hints, etc. Otherwise, it would behave like Inactive relative to any other activity
* Read-only would only permit queries.
* Inactive would not respond.
  • Depending on the intervention, all of these could be useful. user story for draining is where the hardware in a cell is to be re-used and you want to move the workload off but not schedule new VMs. read-only would where, for example, you are doing a database migration and don't want new entries during that migration. Testing would be very useful for larger implementations that regularly add cells to exiting regions and would want to QC them independently from production. Inactive would be where you really don't want the cell to answer. There are probably other components in OpenStack that also exhibit this behavior.


  • Add “state” field to cells table, in the first stage, only ACTIVE and INACTIVE states will be implemented, then additional states could be added as the use cases are clarified.
  • It will extend the existing v3 cells API.
  • Support for nova cli to update state of cell:
# nova help cell-update
usage: nova cell-update <cell-name> <state>

Update state of a given cell.

Positional arguments:
  <cell-name>  Name of the cell.
  <state> Supported states: (ACTIVE | DRAINING | TESTING | READONLY | INACTIVE)

DB Model Changes

  • New table would be like:
Field Type Null Key Default Extra
created_at datetime YES NULL
updated_at datetime YES NULL
deleted_at datetime YES NULL
id int(11) NO PRI NULL
api_url varchar(255) YES NULL
weight_offset float YES NULL
weight_scale float YES NULL
name varchar(255) YES MUL NULL
is_parent tinyint(1) YES NULL
deleted int(11) YES NULL
transport_url varchar(255) NO NULL
state varchar(255) YES NULL

API Spec

  • Change cell state
PUT v3/{tenant_id}/os-cells/update
Response Codes 200
Request parameters
“cell”: {
“id”: “123”,
“state”: “Active/Draining/Testing/ReadOnly/Inactive”