Nova-Cells-v2

Nova Cells v2

Bugs

https://bugs.launchpad.net/nova/+bug/1656276 - Error running nova-manage cell_v2 simple_cell_setup when configuring nova with puppet-nova
- The create_cell CLI should go toward fixing this: https://review.openstack.org/#/c/332713/
https://bugs.launchpad.net/nova/+bug/1649341 - Undercloud upgrade fails with "Cell mappings are not created, but required for Ocata"
- Fixed on master in Nova, backport proposed to stable/newton. However, this change caused issues for TripleO on master which is bug 1656276 above.
https://bugs.launchpad.net/nova/+bug/1656017 - nova-manage cell_v2 map_cell0 always returns a non-0 exit code
- dtp has a fix here: https://review.openstack.org/#/c/420132/
https://bugs.launchpad.net/nova/+bug/1656673 - map_cell0 should use the main DB connection, not the API DB
- dansmith has a fix here: https://review.openstack.org/#/c/420439/
https://bugs.launchpad.net/nova/+bug/1656675 - There is no way to list cell mappings besides looking into the DB
- mriedem has a fix here: https://review.openstack.org/#/c/420440/
https://bugs.launchpad.net/nova/+bug/1656691 - There is no way to delete a cell mapping except via DB directly
- mriedem has a fix here: https://review.openstack.org/#/c/420451/

TODOs

The deployment/upgrade process needs to be documented in more than just the release notes.
- dansmith has a start on the docs here: https://review.openstack.org/#/c/420198/
- (diana will take this) On a side note, we should also have man pages for the cell_v2 commands because there is confusion around the inputs and outputs and how return codes should be treated, i.e. is 1 an error or not? Put the CLI docs here: http://docs.openstack.org/developer/nova/man/nova-manage.html
  - Reviews for those docs: https://review.openstack.org/#/q/status:open+project:openstack/nova+branch:master+topic:man
  - Let me (diana_clarke) know if you want them changed in any way.
- alaski's older docs patch (which is probably out of date now but might be useful) is here: https://review.openstack.org/#/c/267153/
- Summary of current commands:
  - map_cell0: creates a cell mapping for cell0
  - simple_cell_setup: creates a cell mapping for cell0 and creates a cell mapping and associates hosts with it (requires unmapped compute hosts registered already). Intended as a lightweight way for non-cells-v1 users to setup cells v2 during an upgrade.
  - map_cell_and_hosts: creates a cell mapping and associates hosts with it (requires unmapped compute hosts registered already)
  - discover_hosts: associates unmapped hosts with an existing cell mapping (or all cell mappings if a specific cell isn't specified)
- Commands TODO?:
  - create_cell: creates a cell mapping intended for association with hosts later via discover_hosts: https://review.openstack.org/#/c/332713/
  - list_cells: list current cell mappings, noting any that are empty (to help with 1. knowing whether a cell needs to be created 2. finding empty cells for use or for cleanup): https://review.openstack.org/420440
  - delete_cell: delete a cell mapping, for use in cleaning up erroneously created cell mappings or wrong cell mappings, etc: https://review.openstack.org/#/c/420451/
Integrate the 'nova-status upgrade check' CLI into the CI/QA system (grenade).
Older tracking etherpads (these may be out of date):
- https://etherpad.openstack.org/p/cellsV2-remaining-work-items
- https://etherpad.openstack.org/p/nova-multiple-cells

Open Questions

Should the computes self-register with a cell when the compute_nodes record is created from the ResourceTracker? https://review.openstack.org/#/c/369634/
- How would the computes know which cell to map to? We could add something to the model to flag a 'default' or 'staging' cell mapping, or put something into nova.conf on the compute node.
- If we auto-register into a default/staging cell, how do we move hosts to other cells? nova-manage CLI?
Why can't we create an empty cell, i.e. a cell mapping with no computes? This is a fresh-install scenario.
- Note that the nova-status upgrade check command does not consider it a failure if there are cell mappings but no compute nodes yet but simple_cell_setup does consider that a failure, see bug 1656276.
- There has been a review up for this for awhile: https://review.openstack.org/#/c/332713/
  - This way, a fresh install would do something like: 'nova-manage cell_v2 map_cell0' 'nova-manage cell_v2 create_cell' and then once compute hosts are available, operator runs 'nova-manage cell_v2 discover_hosts'

Nova-Cells-v2

Contents

Nova Cells v2

Bugs

TODOs

Open Questions

Manifesto

Testing

DB Table Analysis

Scheduling requirements

Code Review

References