Run metadata-api per cell

Registered by Matt Riedemann

This was discussed at the Stein PTG: (Line 400)

The cells v2 deployment docs say the metadata API service runs globally across cells, but deployers, like CERN and Huawei, run it per cell for performance reasons. All you have to do is make sure the nova configuration has the api_database configured so the metadata-api service can hit the API DB to lookup the instance information.

The downside to this is, if you're running the service per-cell anyway, you don't need to waste time doing that lookup to the API DB when you know the instance will be in that cell.

So this blueprint proposes that, like the old "local conductor" mode, a config option can be set which indicates the metadata-api service is "local" to a cell and therefore can ignore the API DB lookups to improve performance.

The suggested configuration option name would be ``local_metadata_per_cell`` in the [api] group.

Docs will be updated appropriately for the config option, plus tests etc.

Blueprint information

Balazs Gibizer
Matt Riedemann
Zhenyu Zheng
Series goal:
Accepted for stein
Milestone target:
milestone icon stein-3
Started by
Matt Riedemann
Completed by
Matt Riedemann

Related branches



Agreed in the nova meeting [1] that this blueprint can be specless.

(efried) would like to see the actual conf option section/name in the description before this is approved.


(melwitt): Note that during the Nova/Neutron cross project session [2], we determined we'll need to document when it's appropriate to run metadata API service per cell or globally:

"If you have networks that span cells, you might need to run nova-metadata-api global. If your networks are segmented along cell boundaries, then you can run nova-metadata-api per cell.

AGREE: document when you wouldn't want to run global vs per cell"

[2] L632

Agreed to approve this in the Nov 29 nova meeting. -- mriedem 20181129

Gerrit topic:,topic:bp/run-meta-api-per-cell,n,z

Addressed by:
    WIP run metadata api per cell


Work Items

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