Difference between revisions of "Nova-Cells-v2"

Revision as of 14:08, 18 January 2017

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  • alaski's older docs patch (which is probably out of date now but might be useful) is here: https://review.openstack.org/#/c/267153/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'

Manifesto

http://docs.openstack.org/developer/nova/cells.html#manifesto

Testing

https://etherpad.openstack.org/p/nova-cells-testing

DB Table Analysis

https://etherpad.openstack.org/p/nova-cells-table-analysis

Scheduling requirements

https://etherpad.openstack.org/p/nova-cells-scheduling-requirements

Code Review

• https://review.openstack.org/#/q/topic:bp/cells-scheduling-interaction
• Otherwise see the cells v2 section in the Ocata review priorities etherpad: https://etherpad.openstack.org/p/ocata-nova-priorities-tracking
• https://review.openstack.org/#/q/status:open+project:openstack/nova+branch:master+topic:man

References

• Note the original cells wiki is here: https://wiki.openstack.org/wiki/Blueprint-nova-compute-cells
• Kilo design summit etherpad: https://etherpad.openstack.org/p/kilo-nova-cells
• nova-specs: https://review.openstack.org/#/q/status:open+project:openstack/nova-specs+branch:master+topic:bp/cells-instance-mapping,n,z
• Flow diagrams: http://paste.openstack.org/show/144068/
  • https://etherpad.openstack.org/p/nova-cells-flow-diagram commentable version