nova-manage update_cell does not check if the same combination of transport_url and database_connection already exists

[Surya Seetharaman]

Unlike in nova-manage create_cell, in nova-manage update_cell the check for the same combination of transport-url and database_connection does not exist. Hence it allows a user to update a cell's transport-url and database_connection to another existing cell's configuration which can create inconsistency (if a user accidentally does do it) and should not be allowed IMO.

Steps to Reproduce :

-> nova-manage cell_v2 list_cells

+-------+--------------------------------------+-----------------------------------------------------------+--------------------------------------------------------------------+
| Name | UUID | Transport URL | Database Connection |
+-------+--------------------------------------+-----------------------------------------------------------+--------------------------------------------------------------------+
| cell0 | 00000000-0000-0000-0000-000000000000 | none:/ | mysql+pymysql://root:****@127.0.0.1/nova_cell0?charset=utf8 |
| cell1 | 20f9fd43-7295-4f67-8f0c-7828b12f5e4f | rabbit://stackrabbit:****@188.185.83.1:5672/nova_cell1 | mysql+pymysql://root:****@188.185.83.1/nova_cell1?charset=utf8 |
| cell2 | 7acaf644-d181-420b-ac80-486b83793bd2 | rabbit://stackrabbit:****@188.185.83.2:5672/nova_cell1 | mysql+pymysql://root:****@188.185.83.2/nova_cell1?charset=utf8 |
+-------+--------------------------------------+-----------------------------------------------------------+--------------------------------------------------------------------+

-> nova-manage cell_v2 update_cell --cell-uuid 7acaf644-d181-420b-ac80-486b83793bd2 --transport-url rabbit://stackrabbit:****@188.185.83.1:5672/nova_cell1 --database_connection mysql+pymysql://root:****@188.185.83.1/nova_cell1?charset=utf8

Expected result
===============
"Cell with the specified transport_url and database_connection combination already exists"

Actual result
=============

-> nova-manage cell_v2 list_cells

+-------+--------------------------------------+-----------------------------------------------------------+--------------------------------------------------------------------+
| Name | UUID | Transport URL | Database Connection |
+-------+--------------------------------------+-----------------------------------------------------------+--------------------------------------------------------------------+
| cell0 | 00000000-0000-0000-0000-000000000000 | none:/ | mysql+pymysql://root:****@127.0.0.1/nova_cell0?charset=utf8 |
| cell1 | 20f9fd43-7295-4f67-8f0c-7828b12f5e4f | rabbit://stackrabbit:****@188.185.83.1:5672/nova_cell1 | mysql+pymysql://root:****@188.185.83.1/nova_cell1?charset=utf8 |
| cell2 | 7acaf644-d181-420b-ac80-486b83793bd2 | rabbit://stackrabbit:****@188.185.83.1:5672/nova_cell1 | mysql+pymysql://root:****@188.185.83.1/nova_cell1?charset=utf8 |
+-------+--------------------------------------+-----------------------------------------------------------+--------------------------------------------------------------------+

Solution : The same kind of check in nova-manage create_cell needs to be done in nova-manage update_cell as well.

[Matt Riedemann (mriedem)]

Ideally we'd just have a unique constraint across those two columns in the cell_mappings table in the API database, but I'm not sure if there is a case where we'd want more than once cell to have the same db/transport urls, probably not, especially since we don't have a concept of disabled cells.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/518556

[Surya Seetharaman (tssurya)]

mriedem : Is is possible to add a unique constraint to these columns since they of type "Text()". I do not see MYSQL supporting it directly, I see some hashing solution being suggested. Is there a work around that we use in nova ?

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/518556
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=c34e37eef31add8224211b799a56d866c5013fbd
Submitter: Zuul
Branch: master

commit c34e37eef31add8224211b799a56d866c5013fbd
Author: Surya Seetharaman <email address hidden>
Date: Wed Nov 8 15:57:16 2017 +0100

    update_cell allows more than once cell to have the same db/transport url

    Unlike in nova-manage create_cell, in nova-manage update_cell the check
    for the same combination of transport-url and/or database_connection
    does not exist. Hence it allows a user to update a cell's transport-url
    and/or database_connection to another existing cell's transport/db urls.

    Change-Id: Ia5d5566c535d6da3d215392590a2d362e1226424
    Closes-Bug: #1729806

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 17.0.0.0b3 development milestone.